/*
 * Copyright © 2009 CNRS
 * Copyright © 2009-2023 Inria.  All rights reserved.
 * Copyright © 2009-2013 Université Bordeaux
 * Copyright © 2009-2020 Cisco Systems, Inc.  All rights reserved.
 * Copyright © 2020 Hewlett Packard Enterprise.  All rights reserved.
 * See COPYING in top-level directory.
 */

/*! \page hwloc_intro Hardware Locality (hwloc) Introduction

<h1 class="sub">Portable abstraction of hierarchical architectures for high-performance computing</h1>

<hr>

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<div class="section">
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See also \ref further_reading
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or the Related pages tab above
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for links to more sections about hwloc concepts.
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<div class="section" id="hwloc_summary">
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\section hwloc_summary hwloc Summary

hwloc provides command line tools and a C API to obtain the
hierarchical map of key computing elements within a node, such as: NUMA memory
nodes, shared caches, processor packages, dies and cores,
processing units (logical processors or "threads")
and even I/O devices.
hwloc also gathers various attributes such as
cache and memory information, and is portable across a variety of
different operating systems and platforms.

hwloc primarily aims at helping high-performance computing (HPC)
applications, but is also applicable to any project seeking to exploit
code and/or data locality on modern computing platforms.

hwloc supports the following operating systems:

<ul>
<li>Linux (with knowledge of cgroups and cpusets, memory targets/initiators, etc.)
on all supported hardware, including Intel Xeon Phi, ScaleMP vSMP,
and NumaScale NumaConnect.</li>
<li>Solaris (with support for processor sets and logical domains)</li>
<li>AIX</li>
<li>Darwin / OS X</li>
<li>FreeBSD and its variants (such as kFreeBSD/GNU)</li>
<li>NetBSD</li>
<li>HP-UX</li>
<li>Microsoft Windows</li>
<li>IBM BlueGene/Q Compute Node Kernel (CNK)</li>
</ul>

Since it uses standard Operating System information, hwloc's support is mostly
independant from the processor type (x86, powerpc, ...) and just relies on the
Operating System support. The main exception is BSD operating systems (NetBSD, FreeBSD, etc.)
because they do not provide support topology information, hence hwloc uses an x86-only CPUID-based
backend (which can be used for other OSes too, see the \ref plugins section).

To check whether hwloc works on a particular machine, just try to build it
and run <tt>lstopo</tt> or <tt>lstopo-no-graphics</tt>. If some things do not look right
(e.g. bogus or missing cache information), see \ref bugs.

hwloc only reports the number of processors on unsupported operating
systems; no topology information is available.

For development and debugging purposes, hwloc also offers the ability to
work on "fake" topologies:

<ul>
  <li> Symmetrical tree of resources generated from a list of level arities,
  see \ref synthetic.</li>
  <li> Remote machine simulation through the gathering of topology as XML files,
  see \ref xml.</li>
</ul>

hwloc can display the topology in a human-readable format, either in
graphical mode (X11), or by exporting in one of several different
formats, including: plain text, LaTeX tikzpicture, PDF, PNG, and FIG (see \ref cli_examples
below).  Note that some of the export formats require additional
support libraries.

hwloc offers a programming interface for manipulating topologies and
objects. It also brings a powerful CPU bitmap API that is used to
describe topology objects location on physical/logical processors. See
the \ref interface below. It may also be used to binding applications
onto certain cores or memory nodes. Several utility programs are also
provided to ease command-line manipulation of topology objects,
binding of processes, and so on.

Bindings for several other languages are available from the
<a href="https://www.open-mpi.org/projects/hwloc/#language_bindings">project website</a>.


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\section hwloc_installation hwloc Installation

The generic installation procedure for both hwloc and netloc
is described in \ref common_installation.

The hwloc command-line tool "lstopo" produces human-readable topology
maps, as mentioned above.  It can also export maps to the "fig" file
format.  Support for PDF, Postscript, and PNG exporting is provided if
the "Cairo" development package (usually <tt>cairo-devel</tt> or
<tt>libcairo2-dev</tt>) can be found in "lstopo" when hwloc
is configured and build.

The hwloc core may also benefit from the following development packages:
<ul>
<li>libpciaccess for full I/O device discovery
    (<tt>libpciaccess-devel</tt> or <tt>libpciaccess-dev</tt> package).
    On Linux, PCI discovery may still be performed (without vendor/device names)
    even if libpciaccess cannot be used.
</li>

<li>AMD or NVIDIA OpenCL implementations for OpenCL device discovery.
</li>
<li>the NVIDIA CUDA Toolkit for CUDA device discovery.
  See \ref faq_cuda_build.
</li>
<li>the NVIDIA Management Library (NVML) for NVML device discovery.
  It is included in CUDA since version 8.0.
  Older NVML releases were available within the NVIDIA GPU Deployment Kit
  from https://developer.nvidia.com/gpu-deployment-kit .
</li>
<li>the NV-CONTROL X extension library (NVCtrl) for NVIDIA display discovery.
  The relevant development package is usually <tt>libXNVCtrl-devel</tt>
  or <tt>libxnvctrl-dev</tt>.
  It is also available within nvidia-settings from ftp://download.nvidia.com/XFree86/nvidia-settings/
  and https://github.com/NVIDIA/nvidia-settings/ .
</li>
<li>the AMD ROCm SMI library for RSMI device discovery.
  The relevant development package is usually <tt>rocm-smi-lib64</tt>
  or <tt>librocm-smi-dev</tt>.
  See \ref faq_rocm_build.
</li>
<li>the oneAPI Level Zero library.
  The relevant development package is usually <tt>level-zero-dev</tt>
  or <tt>level-zero-devel</tt>.
</li>
<li>libxml2 for full XML import/export support (otherwise, the
    internal minimalistic parser will only be able to import
    XML files that were exported by the same hwloc release).
    See \ref xml for details.
    The relevant development package is usually <tt>libxml2-devel</tt>
    or <tt>libxml2-dev</tt>.
</li>
<li>libudev on Linux for easier discovery of OS device information
    (otherwise hwloc will try to manually parse udev raw files).
    The relevant development package is usually <tt>libudev-devel</tt>
    or <tt>libudev-dev</tt>.
</li>
<li>libtool's ltdl library for dynamic plugin loading if the native dlopen cannot be used.
  The relevant development package is usually <tt>libtool-ltdl-devel</tt>
  or <tt>libltdl-dev</tt>.
</li>
</ul>

PCI and XML support may be statically built inside the main hwloc
library, or as separate dynamically-loaded plugins (see the
\ref plugins section).

Note that because of the possibility of GPL taint, the
<tt>pciutils</tt> library <tt>libpci</tt> will not be used (remember
that hwloc is BSD-licensed).


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\section cli_examples Command-line Examples

On a 4-package 2-core machine with hyper-threading, the \c lstopo tool
may show the following graphical output:

\image html dudley.png
\image latex dudley.png "" width=\textwidth

Here's the equivalent output in textual form:

\verbatim
Machine
  NUMANode L#0 (P#0)
  Package L#0 + L3 L#0 (4096KB)
    L2 L#0 (1024KB) + L1 L#0 (16KB) + Core L#0
      PU L#0 (P#0)
      PU L#1 (P#8)
    L2 L#1 (1024KB) + L1 L#1 (16KB) + Core L#1
      PU L#2 (P#4)
      PU L#3 (P#12)
  Package L#1 + L3 L#1 (4096KB)
    L2 L#2 (1024KB) + L1 L#2 (16KB) + Core L#2
      PU L#4 (P#1)
      PU L#5 (P#9)
    L2 L#3 (1024KB) + L1 L#3 (16KB) + Core L#3
      PU L#6 (P#5)
      PU L#7 (P#13)
  Package L#2 + L3 L#2 (4096KB)
    L2 L#4 (1024KB) + L1 L#4 (16KB) + Core L#4
      PU L#8 (P#2)
      PU L#9 (P#10)
    L2 L#5 (1024KB) + L1 L#5 (16KB) + Core L#5
      PU L#10 (P#6)
      PU L#11 (P#14)
  Package L#3 + L3 L#3 (4096KB)
    L2 L#6 (1024KB) + L1 L#6 (16KB) + Core L#6
      PU L#12 (P#3)
      PU L#13 (P#11)
    L2 L#7 (1024KB) + L1 L#7 (16KB) + Core L#7
      PU L#14 (P#7)
      PU L#15 (P#15)
\endverbatim

Note that there is also an equivalent output in XML that is meant for
exporting/importing topologies but it is hardly readable to human-beings
(see \ref xml for details).

On a 4-package 2-core Opteron NUMA machine
(with two core cores disallowed by the administrator),
the \c lstopo tool may show the following graphical output
(with <tt>\--disallowed</tt> for displaying disallowed objects):

\image html hagrid.png
\image latex hagrid.png "" width=\textwidth

Here's the equivalent output in textual form:

\verbatim
Machine (32GB total)
  Package L#0
    NUMANode L#0 (P#0 8190MB)
    L2 L#0 (1024KB) + L1 L#0 (64KB) + Core L#0 + PU L#0 (P#0)
    L2 L#1 (1024KB) + L1 L#1 (64KB) + Core L#1 + PU L#1 (P#1)
  Package L#1
    NUMANode L#1 (P#1 8192MB)
    L2 L#2 (1024KB) + L1 L#2 (64KB) + Core L#2 + PU L#2 (P#2)
    L2 L#3 (1024KB) + L1 L#3 (64KB) + Core L#3 + PU L#3 (P#3)
  Package L#2
    NUMANode L#2 (P#2 8192MB)
    L2 L#4 (1024KB) + L1 L#4 (64KB) + Core L#4 + PU L#4 (P#4)
    L2 L#5 (1024KB) + L1 L#5 (64KB) + Core L#5 + PU L#5 (P#5)
  Package L#3
    NUMANode L#3 (P#3 8192MB)
    L2 L#6 (1024KB) + L1 L#6 (64KB) + Core L#6 + PU L#6 (P#6)
    L2 L#7 (1024KB) + L1 L#7 (64KB) + Core L#7 + PU L#7 (P#7)
\endverbatim

On a 2-package quad-core Xeon (pre-Nehalem, with 2 dual-core dies into
each package):

\image html emmett.png
\image latex emmett.png "" width=\textwidth

Here's the same output in textual form:

\verbatim
Machine (total 16GB)
  NUMANode L#0 (P#0 16GB)
  Package L#0
    L2 L#0 (4096KB)
      L1 L#0 (32KB) + Core L#0 + PU L#0 (P#0)
      L1 L#1 (32KB) + Core L#1 + PU L#1 (P#4)
    L2 L#1 (4096KB)
      L1 L#2 (32KB) + Core L#2 + PU L#2 (P#2)
      L1 L#3 (32KB) + Core L#3 + PU L#3 (P#6)
  Package L#1
    L2 L#2 (4096KB)
      L1 L#4 (32KB) + Core L#4 + PU L#4 (P#1)
      L1 L#5 (32KB) + Core L#5 + PU L#5 (P#5)
    L2 L#3 (4096KB)
      L1 L#6 (32KB) + Core L#6 + PU L#6 (P#3)
      L1 L#7 (32KB) + Core L#7 + PU L#7 (P#7)
\endverbatim


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</div><div class="section" id="interface">
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\section interface Programming Interface

The basic interface is available in hwloc.h.
Some higher-level functions are available in hwloc/helper.h to reduce
the need to manually manipulate objects and follow links between them.
Documentation for all these is provided later in this document.
Developers may also want to look at hwloc/inlines.h which contains the
actual inline code of some hwloc.h routines, and at this document,
which provides good higher-level topology traversal examples.

To precisely define the vocabulary used by hwloc, a \ref termsanddefs
section is available and should probably be read first.  

Each hwloc object contains a cpuset describing the list of processing
units that it contains.  These bitmaps may be used for
\ref hwlocality_cpubinding and \ref hwlocality_membinding.
hwloc offers an extensive
bitmap manipulation interface in hwloc/bitmap.h.

Moreover, hwloc also comes with additional helpers for
interoperability with several commonly used environments.
See the \ref interoperability section for details.

The complete API documentation is available in a full set of HTML
pages, man pages, and self-contained PDF files (formatted for both
both US letter and A4 formats) in the source tarball in
doc/doxygen-doc/.  

<strong>NOTE:</strong> If you are building the documentation from a
Git clone, you will need to have Doxygen and pdflatex
installed -- the documentation will be built during the normal "make"
process.  The documentation is installed during "make install" to
$prefix/share/doc/hwloc/ and your systems default man page tree (under
$prefix, of course).

\subsection portability Portability

Operating System have varying support for CPU and memory binding,
e.g. while some Operating Systems provide interfaces for all kinds of CPU and
memory bindings, some others provide only interfaces for a limited number of
kinds of CPU and memory binding, and some do not provide any binding interface
at all.  Hwloc's binding functions would then simply return the ENOSYS error
(Function not implemented), meaning that the underlying Operating System
does not provide any interface for them. \ref hwlocality_cpubinding and
\ref hwlocality_membinding provide more information on which hwloc binding functions
should be preferred because interfaces for them are usually available on the
supported Operating Systems.

Similarly, the ability of reporting topology information varies from
one platform to another.
As shown in \ref cli_examples, hwloc can obtain information on a wide
variety of hardware topologies.  However, some platforms and/or
operating system versions will only report a subset of this
information.  For example, on an PPC64-based system with 8 cores
(each with 2 hardware threads) running a default 2.6.18-based kernel
from RHEL 5.4, hwloc is only able to glean information about NUMA
nodes and processor units (PUs).  No information about caches,
packages, or cores is available.

Here's the graphical output from lstopo on this platform when
Simultaneous Multi-Threading (SMT) is enabled:

\image html ppc64-with-smt.png
\image latex ppc64-with-smt.png "" width=\textwidth

And here's the graphical output from lstopo on this platform when SMT is
disabled:

\image html ppc64-without-smt.png
\image latex ppc64-without-smt.png "" width=.5\textwidth

Notice that hwloc only sees half the PUs when SMT is disabled.
PU L#6, for example, seems to change location from NUMA node #0 to #1.
In reality, no PUs "moved" -- they were simply re-numbered when hwloc
only saw half as many (see also Logical index in \ref termsanddefs_indexes).
Hence, PU L#6 in the SMT-disabled picture probably corresponds to
PU L#12 in the SMT-enabled picture.

This same "PUs have disappeared" effect can be seen on other platforms
-- even platforms / OSs that provide much more information than the
above PPC64 system.  This is an unfortunate side-effect of how
operating systems report information to hwloc.

Note that upgrading the Linux kernel on the same PPC64 system
mentioned above to 2.6.34, hwloc is able to discover all the topology
information.  The following picture shows the entire topology layout
when SMT is enabled:

\image html ppc64-full-with-smt.png
\image latex ppc64-full-with-smt.png "" width=\textwidth

Developers using the hwloc API or XML output for portable applications
should therefore be extremely careful to not make any assumptions
about the structure of data that is returned.  For example, per the
above reported PPC topology, it is not safe to assume that PUs will
always be descendants of cores.

Additionally, future hardware may insert new topology elements that
are not available in this version of hwloc.  Long-lived applications
that are meant to span multiple different hardware platforms should
also be careful about making structure assumptions.  For example,
a new element may someday exist between a core and a PU.


\subsection interface_example API Example

The following small C example (available in the source tree as ``doc/examples/hwloc-hello.c'')
prints the topology of the machine and performs some thread and memory binding.
More examples are available in the doc/examples/ directory of the source
tree.

\include examples/hwloc-hello.c

hwloc provides a \c pkg-config executable to obtain relevant compiler
and linker flags.  For example, it can be used thusly to compile
applications that utilize the hwloc library (assuming GNU Make):

\verbatim
CFLAGS += $(shell pkg-config --cflags hwloc)
LDLIBS += $(shell pkg-config --libs hwloc)

hwloc-hello: hwloc-hello.c
        $(CC) hwloc-hello.c $(CFLAGS) -o hwloc-hello $(LDLIBS)
\endverbatim

On a machine 2 processor packages -- each package of
which has two processing cores -- the output from running \c
hwloc-hello could be something like the following:

\verbatim
shell$ ./hwloc-hello
*** Objects at level 0
Index 0: Machine
*** Objects at level 1
Index 0: Package#0
Index 1: Package#1
*** Objects at level 2
Index 0: Core#0
Index 1: Core#1
Index 2: Core#3
Index 3: Core#2
*** Objects at level 3
Index 0: PU#0
Index 1: PU#1
Index 2: PU#2
Index 3: PU#3
*** Printing overall tree
Machine
  Package#0
    Core#0
      PU#0
    Core#1
      PU#1
  Package#1
    Core#3
      PU#2
    Core#2
      PU#3
*** 2 package(s)
*** Logical processor 0 has 0 caches totaling 0KB
shell$ 
\endverbatim



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</div><div class="section" id="history">
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\section history History / Credits

hwloc is the evolution and merger of the libtopology project and the Portable
Linux Processor Affinity (PLPA) (https://www.open-mpi.org/projects/plpa/)
project. Because of functional and ideological overlap, these two code bases
and ideas were merged and released under the name "hwloc" as an Open MPI
sub-project.

libtopology was initially developed by the Inria Runtime Team-Project.
PLPA was initially developed by
the Open MPI development team as a sub-project. Both are now deprecated
in favor of hwloc, which is distributed as an Open MPI sub-project.

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</div><div class="section" id="further_reading">
\endhtmlonly
\section further_reading Further Reading

The documentation chapters include

<ul>
<li> \ref termsanddefs 
<li> \ref tools
<li> \ref envvar
<li> \ref cpu_mem_bind
<li> \ref iodevices
<li> \ref miscobjs
<li> \ref attributes
<li> \ref topoattrs
<li> \ref xml
<li> \ref synthetic
<li> \ref interoperability
<li> \ref threadsafety
<li> \ref plugins
<li> \ref embed
<li> \ref faq
<li> \ref upgrade_to_api_2x
</ul>

Make sure to have had a look at those too!

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</div>
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\page termsanddefs Terms and Definitions 

 
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<div class="section" id="termsanddefs_objects">
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\section termsanddefs_objects Objects

<dl>

<dt>Object</dt>
  <dd>Interesting kind of part of the system, such as a Core, a L2Cache,
  a NUMA memory node, etc. The different types detected by hwloc are
  detailed in the ::hwloc_obj_type_t enumeration.

  There are four kinds of Objects: Memory (NUMA nodes and Memory-side caches), I/O (Bridges, PCI and OS devices),
  Misc, and Normal (everything else, including Machine, Package, Die, Core, PU, CPU Caches, etc.).
  Normal and Memory objects have (non-NULL) CPU sets and nodesets, while I/O and Misc don't.

  Objects are topologically sorted by locality (CPU and node sets)
  into a tree (see \ref termsanddefs_tree).
  </dd>

<dt>Processing Unit (PU)</dt>
  <dd>The smallest processing element that can be represented by a hwloc
  object. It may be a single-core processor, a core of a multicore
  processor, or a single thread in a SMT processor
  (also sometimes called "Logical processor",
   not to be confused with "Logical index of a processor").
  hwloc's PU acronym stands for Processing Unit.
  </dd>

<dt>Package</dt>
  <dd>A processor Package is the physical package that usually gets
  inserted into a socket on the motherboard.
  It is also often called a physical processor or a CPU even if these
  names bring confusion with respect to cores and processing units.
  A processor package usually contains multiple cores
  (and may also be composed of multiple dies).
  hwloc Package objects were called Sockets up to hwloc 1.10.
  </dd>

<dt>NUMA Node</dt>
  <dd>
  An object that contains memory that is directly and byte-accessible
  to the host processors.
  It is usually close to some cores as specified by its CPU set.
  Hence it is attached as a memory child of the object that groups
  those cores together, for instance a Package objects with 4 Core children
  (see \ref termsanddefs_tree).
  </dd>

<dt>Memory-side Cache</dt>
  <dd>
  A cache in front of a specific memory region (e.g. a range of physical addresses).
  It caches all accesses to that region without caring about which core issued the request.
  This is the opposite of usual CPU caches where only accesses from the local cores
  are cached, without caring about the target memory.

  In hwloc, memory-side caches are memory objects placed between their local CPU objects
  (parent) and the target NUMA node memory (child).
  </dd>
</dl>


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</div><div class="section" id="termsanddefs_indexes">
\endhtmlonly
\section termsanddefs_indexes Indexes and Sets

<dl>

<dt>OS or physical index</dt>
  <dd>The index that the operating system (OS) uses to identify the
  object.  This may be completely arbitrary, non-unique, non-contiguous, not
  representative of logical proximity, and may depend on the BIOS
  configuration. That is why hwloc almost never uses them, only in the default
  lstopo output (<tt>P\#x</tt>) and cpuset masks.
  See also \ref faq_indexes.</dd>

<dt>Logical index</dt>
  <dd>Index to uniquely identify objects of the same type and depth,
  automatically computed by hwloc according to the topology.  It expresses
  logical proximity in a generic way, i.e. objects which have adjacent logical
  indexes are adjacent in the topology. That is why hwloc almost always uses
  it in its API, since it expresses logical proximity. They can be shown (as
  <tt>L\#x</tt>) by <tt>lstopo</tt> thanks to the <tt>-l</tt> option.  This index
  is always linear and in
  the range [0, num_objs_same_type_same_level-1].  Think of it as ``cousin
  rank.'' The ordering is based on topology first, and then on OS CPU numbers,
  so it is stable across everything except firmware CPU renumbering.
  "Logical index" should not be confused with "Logical processor". A "Logical
  processor" (which in hwloc we rather call "processing unit" to avoid the
  confusion) has both a physical index (as chosen arbitrarily by BIOS/OS) and a logical
  index (as computed according to logical proximity by hwloc).
  See also \ref faq_indexes.</dd>

<dt>CPU set</dt>
  <dd>The set of processing units (PU) logically included in an object
  (if it makes sense).  They are always expressed using physical
  processor numbers (as announced by the OS).  They are implemented as the
  ::hwloc_bitmap_t opaque structure.  hwloc CPU sets are just masks, they
  do \em not have any relation with an operating system actual binding notion like
  Linux' cpusets.
  I/O and Misc objects do not have CPU sets while all Normal and Memory objects have non-NULL CPU sets.</dd>

<dt>Node set</dt>
  <dd>The set of NUMA memory nodes logically included in an object
  (if it makes sense).  They are always expressed using physical node
  numbers (as announced by the OS).  They are implemented with the
  ::hwloc_bitmap_t opaque structure.
  as bitmaps.
  I/O and Misc objects do not have Node sets while all Normal and Memory objects have non-NULL nodesets.</dd>

<dt>Bitmap</dt>
  <dd>A possibly-infinite set of bits used for describing sets of objects
  such as CPUs (CPU sets) or memory nodes (Node sets). They are implemented
  with the ::hwloc_bitmap_t opaque structure.
</dd>

</dl>


\htmlonly
</div><div class="section" id="termsanddefs_tree">
\endhtmlonly
\section termsanddefs_tree Hierarchy, Tree and Levels

<dl>

<dt>Parent object</dt>
  <dd>The object logically containing the current object, for example
  because its CPU set includes the CPU set of the current object.
  All objects have a non-NULL parent, except the root of the topology (Machine object).
  </dd>

<dt>Ancestor object</dt>
  <dd>The parent object, or its own parent, and so on.</dd>

<dt>Children object(s)</dt>
  <dd>The object (or objects) contained in the current object because
  their CPU set is included in the CPU set of the current object.
  Each object may also contain separated lists for Memory, I/O and Misc object children.
  </dd>

<dt>Arity</dt>
  <dd>The number of normal children of an object.
  There are also specific arities for Memory, I/O and Misc children.
  </dd>

<dt>Sibling objects</dt>
  <dd>Objects in the same children list, which all of them are normal
  children of the same parent, or all of them are Memory children of
  the same parent, or I/O children, or Misc.
  They usually have the same type (and hence are cousins, as well).
  But they may not if the topology is asymmetric.
  </dd>

<dt>Sibling rank</dt>
  <dd>Index to uniquely identify objects which have
  the same parent, and is always in the range [0, arity-1]
  (respectively memory_arity, io_arity or misc_arity for Memory, I/O
  and Misc children of a parent).</dd>

<dt>Cousin objects</dt>
  <dd>Objects of the same type (and depth) as the current object,
  even if they do not have the same parent.</dd>

<dt>Level</dt>
  <dd>Set of objects of the same type and depth. All these objects
  are cousins.

  Memory, I/O and Misc objects also have their own specific levels and (virtual) depth.
  </dd>

<dt>Depth</dt>
  <dd>Nesting level in the object tree, starting from the root object.
  If the topology is symmetric, the depth of a child is equal to the
  parent depth plus one, and an object depth is also equal to the number
  of parent/child links between the root object and the given object.
  If the topology is asymmetric, the difference between some parent
  and child depths may be larger than one when some intermediate levels
  (for instance groups) are missing in only some parts of the machine.

  The depth of the Machine object is always 0 since it is always the
  root of the topology.
  The depth of PU objects is equal to the number of levels in the topology
  minus one.

  Memory, I/O and Misc objects also have their own specific levels and depth.
  </dd>

</dl>

The following diagram can help to understand the vocabulary of the relationships
by showing the example of a machine with two dual core packages (with no
hardware threads); thus, a topology with 5 levels. Each box with rounded corner
corresponds to one ::hwloc_obj_t, containing the values of the different integer
fields (depth, logical_index, etc.), and arrows show to which other ::hwloc_obj_t
pointers point to (first_child, parent, etc.).

The topology always starts with a Machine object as root (depth 0)
and ends with PU objects at the bottom (depth 4 here).

Objects of the same level (cousins) are listed in red boxes and linked
with red arrows.
Children of the same parent (siblings) are linked with blue arrows.

The L2 cache of the last core is intentionally missing to show how asymmetric topologies are handled.
See \ref faq_asymmetric for more information about such strange topologies.

\image html diagram.png
\image latex diagram.eps "" width=\textwidth

It should be noted that for PU objects, the logical index -- as
computed linearly by hwloc -- is not the same as the OS index.

The NUMA node is on the side because it is not part of the main tree
but rather attached to the object that corresponds to its locality
(the entire machine here, hence the root object).
It is attached as a <i>Memory</i> child (in green) and has a virtual depth (negative).
It could also have siblings if there were multiple local NUMA nodes,
or cousins if other NUMA nodes were attached somewhere else in the machine.

I/O or Misc objects could be attached in a similar manner.



\page tools Command-Line Tools 

\htmlonly
<div class="section">
\endhtmlonly

hwloc comes with an extensive C programming interface and several
command line utilities. Each of them is fully documented in its own
manual page; the following is a summary of the available command line
tools.


\htmlonly
</div><div class="section" id="cli_lstopo">
\endhtmlonly
\section cli_lstopo lstopo and lstopo-no-graphics

lstopo (also known as hwloc-ls) displays the
hierarchical topology map of the current system.  The output may be
graphical, ascii-art or textual, and can also be exported to numerous file
formats such as PDF, PNG, XML, and others.
Advanced graphical outputs require the "Cairo" development package
(usually <tt>cairo-devel</tt> or <tt>libcairo2-dev</tt>).

lstopo and lstopo-no-graphics accept the same command-line options.
However, graphical outputs are only available in lstopo.
Textual outputs (those that do not depend on heavy external libraries
such as Cairo) are supported in both lstopo and lstopo-no-graphics.

This command can also display the processes currently bound to a part
of the machine (via the <tt>\--ps</tt> option).

Note that lstopo can read XML files and/or alternate chroot
filesystems and display topological maps representing those systems
(e.g., use lstopo to output an XML file on one system, and then use
lstopo to read in that XML file and display it on a different system).


\htmlonly
</div><div class="section" id="cli_hwloc_bind">
\endhtmlonly
\section cli_hwloc_bind hwloc-bind

hwloc-bind binds processes to specific hardware objects through a
flexible syntax.  A simple example is binding an executable to
specific cores (or packages or bitmaps or ...).  The hwloc-bind(1) man
page provides much more detail on what is possible.

hwloc-bind can also be used to retrieve the current process' binding,
or retrieve the last CPU(s) where a process ran,
or operate on memory binding.

Just like hwloc-calc, the input locations given to hwloc-bind may be
either objects or cpusets (bitmaps as reported by hwloc-calc or hwloc-distrib).


\htmlonly
</div><div class="section" id="cli_hwloc_calc">
\endhtmlonly
\section cli_hwloc_calc hwloc-calc

hwloc-calc is hwloc's Swiss Army Knife command-line tool for converting things.
The input may be either objects or cpusets (bitmaps as reported by another hwloc-calc instance or by hwloc-distrib),
that may be combined by addition, intersection or subtraction.
The output may be expressed as:
<ul>
<li>a cpuset bitmap: This compact opaque representation of objects is useful for shell scripts etc.
It may passed to hwloc command-line tools such as hwloc-calc or hwloc-bind,
or to hwloc command-line options such as <tt>lstopo \--restrict</tt>.</li>
<li>a nodeset bitmap: Another opaque representation that represents memory locality more precisely,
especially if some NUMA nodes are CPU less or if multiple NUMA nodes are local to the same CPUs.</li>
<li>the amount of the equivalent hwloc objects from a specific type, or the list of their indexes.
This is useful for iterating over all similar objects (for instance all cores) within a given
part of a platform.</li>
<li>a hierarchical description of objects,
for instance a thread index within a core within a package.
This gives a better view of the actual location of an object.</li>
</ul>

Moreover, input and/or output may be use either physical/OS object
indexes or as hwloc's logical object indexes.
It eases cooperation with external tools such as taskset or numactl
by exporting hwloc specifications into list of processor or NUMA node
physical indexes.
See also \ref faq_indexes.


\htmlonly
</div><div class="section" id="cli_hwloc_info">
\endhtmlonly
\section cli_hwloc_info hwloc-info

hwloc-info dumps information about the given objects, as well as all its specific attributes.
It is intended to be used with tools such as grep for filtering
certain attribute lines.
When no object is specified, or when <tt>\--topology</tt> is passed,
hwloc-info prints a summary of the topology.
When <tt>\--support</tt> is passed, hwloc-info lists the supported
features for the topology.


\htmlonly
</div><div class="section" id="cli_hwloc_distrib">
\endhtmlonly
\section cli_hwloc_distrib hwloc-distrib

hwloc-distrib generates a set of cpuset bitmaps that are uniformly
distributed across the machine for the given number of processes.
These strings may be used with hwloc-bind to run processes to maximize
their memory bandwidth by properly distributing them across the
machine.


\htmlonly
</div><div class="section" id="cli_hwloc_ps">
\endhtmlonly
\section cli_hwloc_ps hwloc-ps

hwloc-ps is a tool to display the bindings of processes that are
currently running on the local machine.  By default, hwloc-ps only
lists processes that are bound; unbound process (and Linux kernel
threads) are not displayed.


\htmlonly
</div><div class="section" id="cli_hwloc_annotate">
\endhtmlonly
\section cli_hwloc_annotate hwloc-annotate

hwloc-annotate may modify object (and topology) attributes such as string information
(see \ref attributes_info for details) or Misc children objects.
It may also add distances, memory attributes, etc. to the topology.
It reads an input topology from a XML file and outputs
the annotated topology as another XML file.


\htmlonly
</div><div class="section" id="cli_hwloc_diffpatchcompress">
\endhtmlonly
\section cli_hwloc_diffpatchcompress hwloc-diff, hwloc-patch and hwloc-compress-dir

hwloc-diff computes the difference between two topologies
and outputs it to another XML file.

hwloc-patch reads such a difference file and applies to
another topology.

hwloc-compress-dir compresses an entire directory of XML
files by using hwloc-diff to save the differences between
topologies instead of entire topologies.


\htmlonly
</div><div class="section" id="cli_hwloc_dump_hwdata">
\endhtmlonly
\section cli_hwloc_dump_hwdata hwloc-dump-hwdata

hwloc-dump-hwdata is a Linux and x86-specific tool that dumps
(during boot, privileged) some topology and locality information
from raw hardware files (SMBIOS and ACPI tables) to human-readable
and world-accessible files that the hwloc library will later reuse.

Currently only used on Intel Xeon Phi processor platforms.
See \ref faq_knl_dump.

See <tt>HWLOC_DUMPED_HWDATA_DIR</tt> in \ref envvar for details
about the location of dumped files.


\htmlonly
</div><div class="section" id="cli_hwloc_gather">
\endhtmlonly
\section cli_hwloc_gather hwloc-gather-topology and hwloc-gather-cpuid

hwloc-gather-topology is a Linux-specific tool that saves the
relevant topology files of the current machine into a tarball
(and the corresponding lstopo outputs).

hwloc-gather-cpuid is a x86-specific tool that dumps the
result of CPUID instructions on the current machine into
a directory.

The output of hwloc-gather-cpuid is included in the tarball
saved by hwloc-gather-topology when running on Linux/x86.

These files may be used later (possibly offline) for simulating
or debugging a machine without actually running on it.




\page envvar Environment Variables

\htmlonly
<div class="section">
\endhtmlonly

The behavior of the hwloc library and tools may be tuned thanks to the
following environment variables.

<dl>

<dt>HWLOC_XMLFILE=/path/to/file.xml</dt>
  <dd>enforces the discovery from the given XML file as if
  hwloc_topology_set_xml() had been called.
  This file may have been generated earlier with lstopo file.xml.
  For convenience, this backend provides empty binding hooks which just
  return success.  To have hwloc still actually call OS-specific hooks,
  HWLOC_THISSYSTEM should be set 1 in the environment too, to assert that
  the loaded file is really the underlying system.
  See also \ref xml.
  </dd>

<dt>HWLOC_SYNTHETIC=synthetic_description</dt>
  <dd>enforces the discovery through a synthetic description string
  as if hwloc_topology_set_synthetic() had been called.
  For convenience, this backend provides empty binding hooks which just
  return success.
  See also \ref synthetic.
  </dd>

<dt>HWLOC_XML_VERBOSE=1</dt>
<dt>HWLOC_SYNTHETIC_VERBOSE=1</dt>
  <dd>enables verbose messages in the XML or synthetic topology backends.
  hwloc XML backends (see \ref xml) can emit some error messages to
  the error output stream.
  Enabling these verbose messages within hwloc can be useful for
  understanding failures to parse input XML topologies.
  Similarly, enabling verbose messages in the synthetic topology
  backend can help understand why the description string is invalid.
  See also \ref synthetic.
  </dd>

<dt>HWLOC_THISSYSTEM=1</dt>
  <dd>enforces the return value of hwloc_topology_is_thissystem(), as if
  ::HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM was set with hwloc_topology_set_flags().
  It means that it makes hwloc assume that the selected backend provides the
  topology for the system on which we are running, even if it is not the
  OS-specific backend but the XML backend for instance.
  This means making the binding functions actually call the OS-specific
  system calls and really do binding, while the XML backend would otherwise
  provide empty hooks just returning success.
  This can be used for efficiency reasons to first detect the topology once,
  save it to a XML file, and quickly reload it later through the XML
  backend, but still having binding functions actually do bind.
  This also enables support for the variable HWLOC_THISSYSTEM_ALLOWED_RESOURCES.
  </dd>

<dt>HWLOC_THISSYSTEM_ALLOWED_RESOURCES=1</dt>
  <dd>Get the set of allowed resources from the native operating system
  even if the topology was loaded from XML or synthetic description,
  as if ::HWLOC_TOPOLOGY_FLAG_THISSYSTEM_ALLOWED_RESOURCES was set
  with hwloc_topology_set_flags().
  This variable requires the topology to match the current system
  (see the variable HWLOC_THISSYSTEM).
  This is useful when the topology is not loaded directly from the
  local machine (e.g. for performance reason) and it comes with all
  resources, but the running process is restricted to only a part
  of the machine (for instance because of Linux Cgroup/Cpuset).
  </dd>

<dt>HWLOC_ALLOW=all</dt>
  <dd>Totally ignore administrative restrictions such as Linux Cgroups
  and consider all resources (PUs and NUMA nodes) as allowed.
  This is different from setting HWLOC_TOPOLOGY_FLAG_INCLUDE_DISALLOWED
  which gathers all resources but marks the unavailable ones as disallowed.
  </dt>

<dt>HWLOC_HIDE_ERRORS=1</dt>
  <dd>enables or disables verbose reporting of errors.
  The hwloc library may issue warnings to the standard error stream
  when it detects a problem during topology discovery, for instance
  if the operating system (or user) gives contradictory topology
  information.

  By default (1), hwloc only shows critical errors such as invalid
  hardware topology information or invalid configuration.
  If set to 0 (default in lstopo), more errors are displayed,
  for instance a failure to initialize CUDA or NVML.
  If set to 2, no hwloc error messages are shown.

  Note that additional verbose messages may be enabled with
  other variables such as HWLOC_GROUPING_VERBOSE.
  </dd>

<dt>HWLOC_USE_NUMA_DISTANCES=7</dt>
  <dd>enables or disables the use of NUMA distances.
  NUMA distances and memory target/initiator information may be used
  to improve the locality of NUMA nodes, especially CPU-less nodes.
  Bits in the value of this environment variable enable different features:
  Bit 0 enables the gathering of NUMA distances from the operating system.
  Bit 1 further enables the use of NUMA distances to improve the
  locality of CPU-less nodes.
  Bit 2 enables the use of target/initiator information.
  </dd>

<dt>HWLOC_GROUPING=1</dt>
  <dd>enables or disables objects grouping based on distances.
  By default, hwloc uses distance matrices between objects (either read
  from the OS or given by the user) to find groups of close objects.
  These groups are described by adding intermediate Group objects in the topology.
  Setting this environment variable to 0 will disable this grouping.
  This variable supersedes the obsolete HWLOC_IGNORE_DISTANCES variable.
  </dd>

<dt>HWLOC_GROUPING_ACCURACY=0.05</dt>
  <dd>relaxes distance comparison during grouping.
  By default, objects may be grouped if their distances form a minimal
  distance graph. When setting this variable to 0.02, and when
  ::HWLOC_DISTANCES_ADD_FLAG_GROUP_INACCURATE is given, these distances
  do not have to be strictly equal anymore, they may just be equal
  with a 2% error.
  If set to <tt>try</tt> instead of a numerical value, hwloc will try
  to group with perfect accuracy (0, the default), then with 0.01, 0.02,
  0.05 and finally 0.1.
  Numbers given in this environment variable should always use a dot
  as a decimal mark (for instance 0.01 instead of 0,01).</dd>

<dt>HWLOC_GROUPING_VERBOSE=0</dt>
  <dd>enables or disables some verbose messages during grouping.
  If this variable is set to 1, some debug messages will be displayed
  during distance-based grouping of objects even if debug was not specific
  at configure time.
  This is useful when trying to find an interesting distance grouping
  accuracy.</dd>

<dt>HWLOC_CPUKINDS_RANKING=default</dt>
  <dd>change the ranking policy for CPU kinds.
  hwloc tries to rank CPU kinds that are energy efficiency first,
  and then CPUs that are rather high-performance and power hungry.
  <br/>
  By default, if available, the OS-provided efficiency is used for ranking.
  Otherwise, the frequency and/or core types are used when available.
  <br/>
  This environment variable may be set to
  <tt>coretype+frequency</tt>, <tt>coretype+frequency_strict</tt>, <tt>coretype</tt>,
  <tt>frequency</tt>, <tt>frequency_base</tt>, <tt>frequency_max</tt>,
  <tt>forced_efficiency</tt>, <tt>no_forced_efficiency</tt>,
  <tt>default</tt>, or <tt>none</tt>.
  </dd>

<dt>HWLOC_CPUKINDS_MAXFREQ=adjust=10</dt>
  <dd>change the use of the max frequency in the Linux backend.
  hwloc tries to read the base and max frequencies of each core on Linux.
  Some hardware features such as Intel Turbo Boost Max 3.0 make some cores
  report slightly higher max frequencies than others in the same CPU package.
  Despite having slightly different frequencies, these cores are considered
  identical instead of exposing an hybrid CPU.
  Hence, by default, hwloc uniformizes the max frequencies of cores
  that have the same base frequency (higher values are downgraded by up
  to 10%).

  If this environment variable is set to <tt>adjust=X</tt>,
  the 10% threshold is replaced with X.
  If set to 1, max frequencies are not adjusted anymore,
  some homogeneous processors may appear hybrid because of this.
  If set to 0, max frequencies are entirely ignored.
  </dd>

<dt>HWLOC_PCI_LOCALITY=&lt;domain/bus&gt; &lt;cpuset&gt;;...</dt>
<dt>HWLOC_PCI_LOCALITY=/path/to/pci/locality/file</dt>
<dd>changes the locality of I/O devices behing the specified PCI buses.
  If no I/O locality information is available or if the BIOS reports
  incorrect information, it is possible to move a I/O device tree
  (OS and/or PCI devices with optional bridges)
  near a custom set of processors.
  <br/>
  Localities are given either inside the environment variable itself,
  or in the pointed file.
  They may be separated either by semi-colons or by line-breaks.
  Invalid localities are silently ignored, hence it is possible to insert comments between actual localities.
  <br/>
  Each locality contains a domain/bus specification (in hexadecimal numbers as usual)
  followed by a whitespace and a cpuset:
  <ul>
  <li><tt>0001 &lt;cpuset&gt;</tt> specifies the locality of all buses in PCI domain 0000.</li>
  <li><tt>0000:0f &lt;cpuset&gt;</tt> specifies only PCI bus 0f in domain 0000.</li>
  <li><tt>0002:04-0a &lt;cpuset&gt;</tt> specifies a range of buses (from 04 to 0a) within domain 0002.</li>
  </ul>
  Domain/bus specifications should usually match entire hierarchies of buses
  behind a bridge (including primary, secondary and subordinate buses).
  For instance, if hostbridge 0000:00 is above other bridges/switches with buses 0000:01 to 0000:09,
  the variable should be HWLOC_PCI_LOCALITY="0000:00-09 <cpuset>".
  It supersedes the old HWLOC_PCI_0000_00_LOCALCPUS=&lt;cpuset&gt;
  which only works when hostbridges exist in the topology.
  <br/>
  If the variable is defined to empty or invalid, no forced PCI locality is applied
  but hwloc's internal automatic locality quirks are disabled, which means the exact
  PCI locality reported by the platform is used.
  </dd>

<dt>HWLOC_X86_TOPOEXT_NUMANODES=0</dt>
  <dd>use AMD topoext CPUID leaf in the x86 backend to detect NUMA nodes.
  When using the x86 backend, setting this variable to 1 enables the building
  of NUMA nodes from AMD processor CPUID instructions.
  However this strategy does not always reflect BIOS configuration such as NUMA interleaving.
  And node indexes may be different from those of the operating system.
  Hence this should only be used when OS backends are wrong
  and the user is sure that CPUID returns correct NUMA information.
  </dd>

<dt>HWLOC_KEEP_NVIDIA_GPU_NUMA_NODES=0</dt>
  <dd>show or hide NUMA nodes that correspond to NVIDIA GPU memory.
  By default they are ignored to avoid interleaved memory being allocated
  on GPU by mistake.
  Setting this environment variable to 1 exposes these NUMA nodes.
  They may be recognized by the <em>GPUMemory</em> subtype.
  They also have a <em>PCIBusID</em> info attribute to identify the
  corresponding GPU.
  </dd>

<dt>HWLOC_KNL_MSCACHE_L3=0</dt>
  <dd>Expose the KNL MCDRAM in cache mode as a Memory-side Cache instead of a L3.
  hwloc releases prior to 2.1 exposed the MCDRAM cache as a CPU-side L3 cache.
  Now that Memory-side caches are supported by hwloc, it is still exposed
  as a L3 by default to avoid breaking existing applications.
  Setting this environment variable to 1 will expose it as a proper Memory-side cache.
  </dd>

<dt>HWLOC_WINDOWS_PROCESSOR_GROUP_OBJS=0</dt>
  <dd>Expose Windows processor groups as hwloc Group objects.
  By default, these groups are disabled because they may be incompatible
  with the hierarchy of resources that hwloc builds (leading to warnings).
  Setting this variable to 1 reenables the addition of these groups to the topology.

  This variable does not impact the querying of Windows processor groups
  using the dedicated API in hwloc/windows.h, this feature is always supported.
  </dd>

<dt>HWLOC_ANNOTATE_GLOBAL_COMPONENTS=0</dt>
  <dd>Allow components to annotate the topology even if they are
  usually excluded by global components by default.
  Setting this variable to 1 and also setting <tt>HWLOC_COMPONENTS=xml,pci,stop</tt>
  enables the addition of PCI vendor and model info attributes to a XML topology
  that was generated without those names (if pciaccess was missing).
  </dd>

<dt>HWLOC_FSROOT=/path/to/linux/filesystem-root/</dt>
  <dd>switches to reading the topology from the specified
  Linux filesystem root instead of the main file-system root.
  This directory may have been saved previously from another machine
  with <tt>hwloc-gather-topology</tt>.
  <br/>
  One should likely also set <tt>HWLOC_COMPONENTS=linux,stop</tt>
  so that non-Linux backends are disabled
  (the <tt>-i</tt> option of command-line tools takes care of both).
  <br/>
  Not using the main file-system root causes hwloc_topology_is_thissystem()
  to return 0.
  For convenience, this backend provides empty binding hooks which just
  return success.  To have hwloc still actually call OS-specific hooks,
  HWLOC_THISSYSTEM should be set 1 in the environment too, to assert that
  the loaded file is really the underlying system.
  </dd>

<dt>HWLOC_CPUID_PATH=/path/to/cpuid/</dt>
  <dd>forces the x86 backend to read dumped CPUIDs from the given directory
  instead of executing actual x86 CPUID instructions.
  This directory may have been saved previously from another machine
  with <tt>hwloc-gather-cpuid</tt>.
  <br/>
  One should likely also set <tt>HWLOC_COMPONENTS=x86,stop</tt>
  so that non-x86 backends are disabled
  (the <tt>-i</tt> option of command-line tools takes care of both).
  <br/>
  It causes hwloc_topology_is_thissystem() to return 0.
  For convenience, this backend provides empty binding hooks which just
  return success.  To have hwloc still actually call OS-specific hooks,
  HWLOC_THISSYSTEM should be set 1 in the environment too, to assert that
  the loaded CPUID dump is really the underlying system.
  </dd>

<dt>HWLOC_DUMPED_HWDATA_DIR=/path/to/dumped/files/</dt>
  <dd>loads files dumped by <tt>hwloc-dump-hwdata</tt> (on Linux)
  from the given directory.
  The default dump/load directory is configured during build based
  on \--runstatedir, \--localstatedir, and \--prefix options.
  It usually points to <tt>/var/run/hwloc/</tt> in Linux distribution
  packages, but it may also point to <tt>$prefix/var/run/hwloc/</tt>
  when manually installing and only specifying \--prefix.
  </dd>

<dt>HWLOC_COMPONENTS=list,of,components</dt>
  <dd>forces a list of components to enable or disable.
  Enable or disable the given comma-separated list of components
  (if they do not conflict with each other). Component names prefixed with
  <tt>-</tt> are disabled (a single phase may also be disabled).

  Once the end of the list is reached, hwloc falls back to
  enabling the remaining components (sorted by priority) that do not
  conflict with the already enabled ones, and unless explicitly disabled in the
  list.
  If <tt>stop</tt> is met, the enabling loop immediately stops, no
  more component is enabled.

  If <tt>xml</tt> or <tt>synthetic</tt> components are selected,
  the corresponding XML filename or synthetic description string
  should be pass in <tt>HWLOC_XMLFILE</tt> or <tt>HWLOC_SYNTHETIC</tt>
  respectively.

  Since this variable is the low-level and more generic way to
  select components, it takes precedence over environment variables
  for selecting components.

  If the variable is set to an empty string (or set to a single comma),
  no specific component is loaded first, all components are loaded
  in priority order.

  See \ref plugins_select for details.
  </dd>

<dt>HWLOC_COMPONENTS_VERBOSE=1</dt>
  <dd>displays verbose information about components.
  Display messages when components are registered or enabled.
  This is the recommended way to list the available components
  with their priority
  (all of them are <em>registered</em> at startup).
  </dd>

<dt>HWLOC_PLUGINS_PATH=/path/to/hwloc/plugins/:...</dt>
  <dd>changes the default search directory for plugins.
  By default, <tt>$libdir/hwloc</tt> is used.
  The variable may contain several colon-separated directories.
  </dd>

<dt>HWLOC_PLUGINS_VERBOSE=1</dt>
  <dd>displays verbose information about plugins.
  List which directories are scanned, which files are loaded,
  and which components are successfully loaded.
  </dd>

<dt>HWLOC_PLUGINS_BLACKLIST=filename1,filename2,...</dt>
  <dd>prevents plugins from being loaded if their filename
  (without path) is listed.
  Plugin filenames may be found in verbose messages outputted
  when HWLOC_PLUGINS_VERBOSE=1.
  </dd>

<dt>HWLOC_DEBUG_VERBOSE=0</dt>
  <dd>disables all verbose messages that are enabled by default
  when <tt>--enable-debug</tt> is passed to configure.
  When set to more than 1, even more verbose messages are displayed.
  The default is 1.
  </dd>

</dl>

<!-- not documented:
 HWLOC_USE_DT
  enables the use of the POWER Device-Tree on Linux (disabled by default since 2.1)
 HWLOC_KNL_NUMA_QUIRK
  disables the KNL NUMA Cluster quirk in the linux backend
 HWLOC_KNL_HDH_FALLBACK
  if 1, ignore KNL info from hwloc-dump-hwdata and fallback to heuristic
  if 0, never fallback to the hardwired heuristic, useful if the heuristic is wrong
 HWLOC_DEBUG_ALLOW_OVERLAPPING_NODE_CPUSETS
  don't ignore linux numa nodes with overlapping cpusets
 HWLOC_DEBUG_SORT_CHILDREN
  sort osdev I/O children by name to make sure the topology doesn't depend
  on the ordering of dentries in the local filesystem (for Linux fsroot tests)
 HWLOC_DEBUG_CHECK
  runs sanity checks during discovery, as if \--enable-debug was passed but
  without debug messages
  may be useful in the doc for debugging?
 HWLOC_HIDE_DEPRECATED
  hides some warnings about deprecated features.
  listed in those warnings so no need to document it
 HWLOC_TEST_GATHER_TOPOLOGY=0
  disable the hwloc-gather-topology test when too long on large servers
 HWLOC_FORCE_BGQ
  makes the bgq component run even if it doesn't recognize the running platform as a BGQ/CNK
 HWLOC_PICL_HETEROGENEOUS
  don't apply PICL info from a single CPU to all CPUs since the machine isn't homogeneous
 HWLOC_DEBUG_FAKE_COMPONENT
  enables debugging message to check that the fake component gets loaded
 HWLOC_DONT_ADD_VERSION_INFO
  do not add hwlocVersion and processName info attributes (to facilitate comparing outputs)
 HWLOC_LIBXML=0
 HWLOC_LIBXML_EXPORT=0
 HWLOC_LIBXML_IMPORT=0
  forces the use of the nolibxml XML backend instead of libxml2 if available,
  for both import and export, or only one
 HWLOC_LIBXML_CLEANUP
  cleanup libxml when ending import, to make valgrind happy
  not enabled by default because somebody else may be using libxml
 HWLOC_XML_USERDATA_NOT_DECODED
  do not decode base64 userdata on import,
  and reexport it the same (used by tools for leaving userdata untouched)
 HWLOC_XML_SUPPORT_EXPORT=0
  don't export support info to XML.
 HWLOC_RSMI_SHUTDOWN
  force rsmi_shutdown to make valgrind happy
  not enabled by default on rsmi <= 3.3.x because those old libs do not
  refcount and somebody else might be using rsmi
 HWLOC_NVML_USE_OPENCAPI_LOCALITY
  use the OpenCAPI bridge locality for finding the CPU where a NVLink
  OpenCAPI endpoint is connecter. this may be wrong on POWER8, that's
  why we use the GPU locality instead (assuming GPU have PCIe and
  NVLink connecting to the same socket).
HWLOC_DARWIN_CPUKINDS_FROM_SYSCTL=0
  By default, darwin cpukinds are read from IOKit (device-tree)
  because it's more precise than sysctl hw.perflevel* keys.
  If IOKit cannot be matched with perflevel cache information
  (e.g. if new cluster_type are added beyond E and P),
  sysctl is used instead.
  Setting this variable to 1 forces sysctl.
-->




\page cpu_mem_bind CPU and Memory Binding Overview

\htmlonly
<div class="section">
\endhtmlonly

Some operating systems do not systematically provide separate
functions for CPU and memory binding.  This means that CPU binding
functions may have have effects on the memory binding policy.
Likewise, changing the memory binding policy may change the CPU
binding of the current thread.  This is often not a problem for
applications, so by default hwloc will make use of these functions
when they provide better binding support.

If the application does not want the CPU binding to change when
changing the memory policy, it needs to use the
::HWLOC_MEMBIND_NOCPUBIND flag to prevent hwloc from using OS functions
which would change the CPU binding.  Additionally,
::HWLOC_CPUBIND_NOMEMBIND can be passed to CPU binding function to
prevent hwloc from using OS functions would change the memory binding
policy.  Of course, using these flags will reduce hwloc's overall support for
binding, so their use is discouraged.

One can avoid using these flags but still closely control both memory
and CPU binding by allocating memory, touching each page in the
allocated memory, and then changing the CPU binding.  The
already-really-allocated memory will then be "locked" to physical
memory and will not be migrated.  Thus, even if the memory binding
policy gets changed by the CPU binding order, the already-allocated
memory will not change with it.  When binding and allocating further
memory, the CPU binding should be performed again in case the memory
binding altered the previously-selected CPU binding.

Not all operating systems support the notion of a "current" memory
binding policy for the current process, but such operating systems often still
provide a way to allocate data on a given node set.  Conversely, some
operating systems support the notion of a "current" memory binding policy and do
not permit allocating data on a specific node set without changing the
current policy and allocate the data. To provide the most powerful coverage of
these facilities, hwloc provides:

<ul>
<li>functions that set/get the current memory binding policies (if supported):
hwloc_set/get_membind() and hwloc_set/get_proc_membind()
<li>a function that allocates memory bound to specific node set without changing
the current memory binding policy (if supported): hwloc_alloc_membind().
<li>a helper which, if needed, changes the current memory binding policy of the
process in order to obtain memory binding: hwloc_alloc_membind_policy().
</ul>

An application can thus use the two first sets of functions if it wants to
manage separately the global process binding policy and directed allocation,
or use the third set of functions if it does not care about the process memory
binding policy.

See \ref hwlocality_cpubinding and \ref hwlocality_membinding for
hwloc's API functions regarding CPU and memory binding, respectively.
There are some examples under doc/examples/ in the source tree.



\page iodevices I/O Devices

\htmlonly
<div class="section">
\endhtmlonly

hwloc usually manipulates processing units and memory but it can also
discover I/O devices and report their locality as well.
This is useful for placing I/O intensive applications on cores near the
I/O devices they use, or for gathering information about all platform
components.


\htmlonly
</div><div class="section" id="iodevices_enabling">
\endhtmlonly
\section iodevices_enabling Enabling and requirements

I/O discovery is disabled by default (except in lstopo) for performance
reasons.
It can be enabled by changing the filtering of I/O object types to
<tt>::HWLOC_TYPE_FILTER_KEEP_IMPORTANT</tt> or <tt>::HWLOC_TYPE_FILTER_KEEP_ALL</tt>
before loading the topology, for instance with <tt>hwloc_topology_set_io_types_filter()</tt>.

Note that I/O discovery requires significant help from the operating system.
The pciaccess library (the development package is usually <tt>libpciaccess-devel</tt>
or <tt>libpciaccess-dev</tt>) is needed to fully detect PCI devices and bridges/switches.
On Linux, PCI discovery may still be performed even if <tt>libpciaccess</tt> cannot
be used. But it misses PCI device names.
Moreover, some operating systems require privileges for probing PCI devices,
see \ref faq_privileged for details.

The actual locality of I/O devices is only currently detected on Linux.
Other operating system will just report I/O devices as being attached
to the topology root object.


\htmlonly
</div><div class="section" id="iodevices_objects">
\endhtmlonly
\section iodevices_objects I/O objects

When I/O discovery is enabled and supported, some additional objects
are added to the topology.
The corresponding I/O object types are:
<ul><li>
<tt>::HWLOC_OBJ_OS_DEVICE</tt> describes an operating-system-specific
handle such as the <em>sda</em> drive or the <em>eth0</em> network interface.
See \ref iodevices_osdev.
</li><li>
<tt>::HWLOC_OBJ_PCI_DEVICE</tt> and <tt>::HWLOC_OBJ_BRIDGE</tt> build up
a PCI hierarchy made of bridges (that may be actually be switches) and devices.
See \ref iodevices_pci.
</li></ul>
Any of these types may be filtered individually with <tt>hwloc_topology_set_type_filter()</tt>.

hwloc tries to attach these new objects to normal objects
(usually NUMA nodes) to match their actual physical location.
For instance, if a I/O hub (or root complex) is physically connected to a package,
the corresponding hwloc bridge object (and its PCI bridges and devices children)
is inserted as a child of the corresponding hwloc Package object.
<b>These children are not in the normal children list but rather in the I/O-specific
children list.</b>

I/O objects also have neither CPU sets nor node sets (NULL pointers) because
they are not directly usable by the user applications for binding.
Moreover I/O hierarchies may be highly complex (asymmetric trees of bridges).
So I/O objects are placed in specific levels with custom depths.
Their lists may still be traversed with regular helpers such as
hwloc_get_next_obj_by_type().
However, hwloc offers some dedicated helpers such as hwloc_get_next_pcidev()
and hwloc_get_next_osdev() for convenience (see \ref hwlocality_advanced_io).


\htmlonly
</div><div class="section" id="iodevices_osdev">
\endhtmlonly
\section iodevices_osdev OS devices

Although each PCI device is uniquely identified by its bus ID
(e.g. 0000:01:02.3), a user-space application can hardly find out which
PCI device it is actually using.
Applications rather use software handles
(such as the <em>eth0</em> network interface,
 the <em>sda</em> hard drive,
 or the <em>mlx4_0</em> OpenFabrics HCA).
Therefore hwloc tries to add software devices
(<tt>::HWLOC_OBJ_OS_DEVICE</tt>, also known as OS devices).

OS devices may be attached below PCI devices, but they may also be
attached directly to normal objects.
Indeed some OS devices are not related to PCI.
For instance, NVDIMM block devices (such as <em>pmem0s</em> on Linux)
are directly attached near their NUMA node
(I/O child of the parent whose memory child is the NUMA node).
Also, if hwloc could not discover PCI for some reason, PCI-related
OS devices may also be attached directly to normal objects.

Finally, OS <em>subdevices</em> may be exposed as OS devices children
of another OS device. This is the case of LevelZero subdevices for instance.

hwloc first tries to discover OS devices from the operating system,
e.g. <em>eth0</em>, <em>sda</em> or <em>mlx4_0</em>.
However, this ability is currently only available on Linux for some
classes of devices.

hwloc then tries to discover software devices through additional
I/O components using external libraries.
For instance proprietary graphics drivers do not expose any named OS device,
but hwloc may still create one OS object per software handle when
supported.
For instance the <tt>opencl</tt> and <tt>cuda</tt> components may
add some <em>opencl0d0</em> and <em>cuda0</em> OS device objects.

Here is a list of OS device objects commonly created by hwloc
components when I/O discovery is enabled and supported.

<ul>
<li>Hard disks or non-volatile memory devices (::HWLOC_OBJ_OSDEV_BLOCK)
 <ul>
 <li><em>sda</em> or <em>dax2.0</em> (Linux component)</li>
 </ul>
</li>
<li>Network interfaces (::HWLOC_OBJ_OSDEV_NETWORK)
 <ul>
 <li><em>eth0</em>, <em>wlan0</em>, <em>ib0</em> (Linux component)</li>
 <li><em>hsn0</em> with "Slingshot" subtype for HPE Cray HSNs (Linux component).</li>
 </ul>
</li>
<li>OpenFabrics (InfiniBand, Omni-Path, usNIC, etc) HCAs (::HWLOC_OBJ_OSDEV_OPENFABRICS)
 <ul>
 <li><em>mlx5_0</em>, <em>hfi1_0</em>, <em>qib0</em>, <em>usnic_0</em> (Linux component)</li>
 <li><em>bxi0</em> with "BXI" subtype for Atos/Bull BXI HCAs (Linux component) even if those are not really OpenFabrics.</li>
 </ul>
</li>
<li>GPUs (::HWLOC_OBJ_OSDEV_GPU)
 <ul>
 <li><em>rsmi0</em> for the first RSMI device
  ("RSMI" subtype, from the RSMI component, using the AMD ROCm SMI library)</li>
 <li><em>nvml0</em> for the first NVML device
  ("NVML" subtype, from the NVML component, using the NVIDIA Management Library)</li>
 <li><em>:0.0</em> for the first display
  ("Display" subtype, from the GL component, using the NV-CONTROL X extension library, NVCtrl)</li>
 <li><em>card0</em> and <em>renderD128</em> for DRM device files
  (from the Linux component, filtered-out by default because considered non-important)</li>
 </ul>
</li>
<li>Co-Processors (::HWLOC_OBJ_OSDEV_COPROC)
 <ul>
 <li><em>opencl0d0</em> for the first device of the first OpenCL platform,
  <em>opencl1d3</em> for the fourth device of the second OpenCL platform
  ("OpenCL" subtype, from the  OpenCL component)</li>
 <li><em>ze0</em> for the first Level Zero device
  ("LevelZero" subtype, from the levelzero component, using the oneAPI Level Zero library),
  and <em>ze0.1</em> for its second subdevice (if any).</li>
 <li><em>cuda0</em> for the first NVIDIA CUDA device
  ("CUDA" subtype, from the CUDA component, using the NVIDIA CUDA Library)</li>
 <li><em>ve0</em> for the first NEC Vector Engine device
  ("VectorEngine" subtype, from the Linux component)</li>
 </ul>
</li>
<li>DMA engine channel (::HWLOC_OBJ_OSDEV_DMA)
 <ul>
 <li><em>dma0chan0</em> (Linux component) when all OS devices are enabled (::HWLOC_TYPE_FILTER_KEEP_ALL)</li>
 </ul>
</li>
</ul>

Note that some PCI devices may contain multiple software devices
(see the example below).

See also \ref interoperability for managing these devices without
considering them as hwloc objects.


\htmlonly
</div><div class="section" id="iodevices_pci">
\endhtmlonly
\section iodevices_pci PCI devices and bridges

A PCI hierarchy is usually organized as follows:
A hostbridge object ( <tt>::HWLOC_OBJ_BRIDGE</tt> object with upstream
type <em>Host</em> and downstream type <em>PCI</em>) is attached below
a normal object (usually the entire machine or a NUMA node).
There may be multiple hostbridges in the machine, attached to
different places, but all PCI devices are below one of them
(unless the Bridge object type is filtered-out).

Each hostbridge contains one or several children, either other bridges
(usually PCI to PCI switches) or PCI devices (<tt>::HWLOC_OBJ_PCI_DEVICE</tt>).
The number of bridges between the hostbridge and a PCI device depends
on the machine.


\htmlonly
</div><div class="section" id="iodevices_consult">
\endhtmlonly
\section iodevices_consult Consulting I/O devices and binding

I/O devices may be consulted by traversing the topology manually
(with usual routines such as hwloc_get_obj_by_type()) or by using
dedicated helpers (such as hwloc_get_pcidev_by_busid(), see
\ref hwlocality_advanced_io).

I/O objects do not actually contain any locality information because
their CPU sets and node sets are NULL.
Their locality must be retrieved by walking up the object tree
(through the <tt>parent</tt> link) until a non-I/O object is found
(see hwloc_get_non_io_ancestor_obj()).
This normal object should have non-NULL CPU sets and node sets
which describe the processing units and memory that are immediately
close to the I/O device.
For instance the path from a OS device to its locality may go
across a PCI device parent, one or several bridges, up to
a Package node with the same locality.

Command-line tools are also aware of I/O devices.
lstopo displays the interesting ones by default
(passing <tt>\--no-io</tt> disables it).

hwloc-calc and hwloc-bind may manipulate I/O devices specified
by PCI bus ID or by OS device name.
<ul>
<li>
 <tt>pci=0000:02:03.0</tt> is replaced by the set
 of CPUs that are close to the PCI device whose bus ID is given.
</li>
<li>
 <tt>os=eth0</tt> is replaced by CPUs that are close to the I/O
 device whose software handle is called <tt>eth0</tt>.
</li>
</ul>
This enables easy binding of I/O-intensive applications near the
device they use.


\htmlonly
</div><div class="section" id="iodevices_examples">
\endhtmlonly
\section iodevices_examples Examples

The following picture shows a dual-package dual-core host whose
PCI bus is connected to the first package and NUMA node.

\image html devel09-pci.png
\image latex devel09-pci.png "" width=\textwidth

Six interesting PCI devices were discovered.
However, hwloc found some corresponding software devices
(<em>eth0</em>, <em>eth1</em>, <em>sda</em>, <em>mlx4_0</em>,
<em>ib0</em>, and <em>ib1</em>) for only four of these physical
devices.
The other ones (<em>PCI 102b:0532</em> and <em>PCI 8086:3a20</em>)
are an unused IDE controller (no disk attached)
and a graphic card (no corresponding software device reported
to the user by the operating system).

On the contrary, it should be noted that three different software
devices were found for the last PCI device (<em>PCI 15b3:634a</em>).
Indeed this OpenFabrics HCA PCI device object contains one
one OpenFabrics software device (<em>mlx4_0</em>) and two virtual
network interface software devices (<em>ib0</em> and <em>ib1</em>).


Here is the corresponding textual output:

\verbatim
Machine (24GB total)
  Package L#0
    NUMANode L#0 (P#0 12GB)
    L3 L#0 (8192KB)
      L2 L#0 (256KB) + L1 L#0 (32KB) + Core L#0 + PU L#0 (P#0)
      L2 L#1 (256KB) + L1 L#1 (32KB) + Core L#1 + PU L#1 (P#2)
    HostBridge
      PCIBridge
        PCI 01:00.0 (Ethernet)
          Net "eth0"
        PCI 01:00.1 (Ethernet)
          Net "eth1"
      PCIBridge
        PCI 03:00.0 (RAID)
          Block "sda"
      PCIBridge
        PCI 04:03.0 (VGA)
      PCI 00:1f.2 (IDE)
      PCI 51:00.0 (InfiniBand)
        Net "ib0"
        Net "ib1"
        Net "mlx4_0"
  Package L#1
    NUMANode L#1 (P#1 12GB)
    L3 L#1 (8192KB)
      L2 L#2 (256KB) + L1 L#2 (32KB) + Core L#2 + PU L#2 (P#1)
      L2 L#3 (256KB) + L1 L#3 (32KB) + Core L#3 + PU L#3 (P#3)
\endverbatim




\page miscobjs Miscellaneous objects

\htmlonly
<div class="section">
\endhtmlonly

hwloc topologies may be annotated with Misc objects
(of type <tt>::HWLOC_OBJ_MISC</tt>)
either automatically or by the user.
This is a flexible way to annotate topologies with
large sets of information since Misc objects may be inserted
anywhere in the topology (to annotate specific objects or
parts of the topology), even below other Misc objects, and each
of them may contain multiple attributes (see also \ref faq_annotate).

These Misc objects may have a <tt>subtype</tt> field
to replace <tt>Misc</tt> with something else in the lstopo
output.


\htmlonly
</div><div class="section" id="miscobjs_auto">
\endhtmlonly
\section miscobjs_auto Misc objects added by hwloc

hwloc only uses Misc objects when other object types are not sufficient,
and when the Misc object type is not filtered-out anymore.
This currently includes:
<ul>
<li>
Memory modules (DIMMs), on Linux when privileged and when
<tt>dmi-sysfs</tt> is supported by the kernel.
These objects have a <tt>subtype</tt> field of value <tt>MemoryModule</tt>.
They are currently always attached to the root object.
Their attributes describe the DIMM vendor, model, etc.
<tt>lstopo -v</tt> displays them as:
\code
Misc(MemoryModule) (P#1 DeviceLocation="Bottom-Slot 2(right)" BankLocation="BANK 2" Vendor=Elpida SerialNumber=21733667 AssetTag=9876543210 PartNumber="EBJ81UG8EFU0-GN-F ")
\endcode
</li>
<li>
Displaying process binding in <tt>lstopo \--top</tt>.
These objects have a <tt>subtype</tt> field of value <tt>Process</tt>
and a name attribute made of their PID and program name.
They are attached below the object they are bound to.
The textual <tt>lstopo</tt> displays them as:
\code
  PU L#0 (P#0)
    Misc(Process) 4445 myprogram
\endcode
</li>
</ul>


\htmlonly
</div><div class="section" id="miscobjs_annotate">
\endhtmlonly
\section miscobjs_annotate Annotating topologies with Misc objects

The user may annotate hwloc topologies with its own Misc objects.
This can be achieved with <tt>hwloc_topology_insert_misc_object()</tt>
as well as hwloc-annotate command-line tool.




\page attributes Object attributes

\htmlonly
<div class="section" id="attributes_normal">
\endhtmlonly
\section attributes_normal Normal attributes

hwloc objects have many generic attributes in the ::hwloc_obj structure,
for instance their <tt>logical_index</tt> or <tt>os_index</tt>
(see \ref faq_indexes), <tt>depth</tt> or <tt>name</tt>.

The kind of object is first described by the <tt>obj->type</tt>
generic attribute (an integer).
OS devices also have a specific <tt>obj->attr->osdev.type</tt> integer
for distinguishing between NICs, GPUs, etc.

Objects may also have an optional <tt>obj->subtype</tt> pointing
to a better description string (displayed by lstopo either
in place or after the main <tt>obj->type</tt> attribute):
<ul>
<li>NUMA nodes:
subtype <tt>DRAM</tt> (for usual main memory),
<tt>HBM</tt> (high-bandwidth memory),
<tt>SPM</tt> (specific-purpose memory, usually reserved for some custom applications),
<tt>NVM</tt> (non-volatile memory when used as main memory),
<tt>MCDRAM</tt> (on KNL)
or <tt>GPUMemory</tt> (on POWER architecture with NVIDIA GPU memory shared over NVLink).
</li>
<li>Groups:
subtype <tt>Cluster</tt>, <tt>Module</tt>, <tt>Tile</tt>, <tt>Compute Unit</tt>,
<tt>Book</tt> or <tt>Drawer</tt> for different architecture-specific groups of CPUs
(see also \ref faq_groups).
</li>
<li>OS devices (see also \ref iodevices_osdev):
<ul>
<li>Co-processor: subtype <tt>OpenCL</tt>, <tt>LevelZero</tt>, <tt>CUDA</tt>, or <tt>VectorEngine</tt>.</li>
<li>GPU: subtype <tt>RSMI</tt> (AMD GPU) or <tt>NVML</tt> (NVIDIA GPU).</li>
<li>OpenFabrics: subtype <tt>BXI</tt> (Bull/Atos BXI HCA).</li>
<li>Network: subtype <tt>Slingshot</tt> (HPE Cray Slingshot Cassini HSN).</li>
<li>Block: subtype <tt>Disk</tt>, <tt>NVM</tt> (non-volatile memory), <tt>SPM</tt> (specific-purpose memory), <tt>CXLMem</tt> (CXL volatile ou persistent memory), <tt>Tape</tt>, or <tt>Removable Media Device</tt>.</li>
</ul>
</li>
<li>L3 Caches:
subtype <tt>MemorySideCache</tt> when hwloc is configured to expose
the KNL MCDRAM in Cache mode as a L3.
</li>
<li>PCI devices:
subtype <tt>NVSwitch</tt> for NVLink switches
(see also NVLinkBandwidth in \ref topoattrs_distances).
</li>
<li>Misc devices:
subtype <tt>MemoryModule</tt>
(see also \ref miscobjs_auto)
</li>
</ul>

Each object also contains an <tt>attr</tt> field that, if non NULL,
points to a union ::hwloc_obj_attr_u of type-specific attribute
structures.
For instance, a L2Cache object <tt>obj</tt> contains cache-specific
information in <tt>obj->attr->cache</tt>, such as its size and
associativity, cache type.
See ::hwloc_obj_attr_u for details.


\htmlonly
</div><div class="section" id="attributes_info">
\endhtmlonly
\section attributes_info Custom string infos

Aside os these generic attribute fields, hwloc annotates
many objects with string attributes that are made of a key and a
value.
Each object contains a list of such pairs that may be consulted
manually (looking at the object <tt>infos</tt> array field)
or using the hwloc_obj_get_info_by_name().
The user may additionally add new key-value pairs to any object using
hwloc_obj_add_info() or the \ref cli_hwloc_annotate program.

Here is a non-exhaustive list of attributes that may be automatically
added by hwloc.
Note that these attributes heavily depend on the ability of the
operating system to report them.
Many of them will therefore be missing on some OS.

\htmlonly
</div><div class="subsection" id="attributes_info_platform">
\endhtmlonly
\subsection attributes_info_platform Hardware Platform Information

These info attributes are attached to the root object (Machine).

<dl>
<dt>PlatformName, PlatformModel, PlatformVendor, PlatformBoardID, PlatformRevision,</dt>
<dt> SystemVersionRegister, ProcessorVersionRegister (Machine)</dt>
<dd>Some POWER/PowerPC-specific attributes describing the platform
and processor.
Currently only available on Linux.
Usually added to Package objects, but can be in Machine instead if
hwloc failed to discover any package.
</dd>
<dt>DMIBoardVendor, DMIBoardName, etc.</dt>
<dd>DMI hardware information such as the motherboard and chassis
models and vendors, the BIOS revision, etc.,
as reported by Linux under <tt>/sys/class/dmi/id/</tt>.
</dd>
<dt>MemoryMode, ClusterMode</dt>
<dd>
Intel Xeon Phi processor configuration modes.
Available if hwloc-dump-hwdata was used (see \ref faq_knl_dump)
or if hwloc managed to guess them from the NUMA configuration.

The memory mode may be <em>Cache</em>, <em>Flat</em>,
<em>Hybrid50</em> (half the MCDRAM is used as a cache)
or <em>Hybrid25</em> (25% of MCDRAM as cache).
The cluster mode may be <em>Quadrant</em>, <em>Hemisphere</em>, <em>All2All</em>,
<em>SNC2</em> or <em>SNC4</em>.
See doc/examples/get-knl-modes.c in the source directory for an example of retrieving these attributes.
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_os">
\endhtmlonly
\subsection attributes_info_os Operating System Information

These info attributes are attached to the root object (Machine).

<dl>
<dt>OSName, OSRelease, OSVersion, HostName, Architecture</dt>
<dd>The operating system name, release, version, the hostname and the
architecture name, as reported by the Unix <tt>uname</tt> command.
</dd>
<dt>LinuxCgroup</dt>
<dd>The name the Linux control group where the calling process is
placed.
</dd>
<dt>WindowsBuildEnvironment</dt>
<dd>Either MinGW or Cygwin when one of these environments was used during build.
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_hwloc">
\endhtmlonly
\subsection attributes_info_hwloc hwloc Information

Unless specified, these info attributes are attached to the root object (Machine).

<dl>
<dt>Backend (topology root, or specific object added by that backend)</dt>
<dd>The name of the hwloc backend/component that filled the topology.
If several components were combined, multiple Backend keys may exist,
with different values, for instance <tt>x86</tt> and <tt>Linux</tt> in the root
object and <tt>CUDA</tt> in CUDA OS device objects.
</dd>
<dt>SyntheticDescription</dt>
<dd>The description string that was given to hwloc to build this
synthetic topology.
</dd>
<dt>hwlocVersion</dt>
<dd>The version number of the hwloc library that was used to generate
the topology. If the topology was loaded from XML, this is not the hwloc
version that loaded it, but rather the first hwloc instance that exported
the topology to XML earlier.
</dd>
<dt>ProcessName</dt>
<dd>The name of the process that contains the hwloc library that was used
to generate the topology. If the topology was from XML, this is not the
hwloc process that loaded it, but rather the first process that exported
the topology to XML earlier.
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_cpu">
\endhtmlonly
\subsection attributes_info_cpu CPU Information

These info attributes are attached to Package objects,
or to the root object (Machine) if package locality information is missing.

<dl>
<dt>CPUModel</dt>
<dd>The processor model name.</dd>
<dt>CPUVendor, CPUModelNumber, CPUFamilyNumber, CPUStepping</dt>
<dd>The processor vendor name, model number, family number, and stepping number.
Currently available for x86 and Xeon Phi processors on most systems,
and for ia64 processors on Linux (except CPUStepping).
</dd>
<dt>CPURevision</dt>
<dd>
A POWER/PowerPC-specific general processor revision number,
currently only available on Linux.
</dd>
<dt>CPUType</dt>
<dd>
A Solaris-specific general processor type name, such as "i86pc".
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_osdev">
\endhtmlonly
\subsection attributes_info_osdev OS Device Information

These info attributes are attached to OS device objects specified in parentheses.

<dl>
<dt>Vendor, Model, Revision, SerialNumber, Size, SectorSize (Block OS devices)</dt>
<dd>The vendor and model names, revision, serial number, size (in KiB = 1024 bytes)
and SectorSize (in bytes).
</dd>
<dt>LinuxDeviceID (Block OS devices)</dt>
<dd>The major/minor device number such as 8:0 of Linux device.
</dd>
<dt>CXLRAMSize, CXLPMEMSize (CXL Memory Block OS devices)</dt>
<dd>The size of the volatile (RAM) or persistent (PMEM) memory
 in a CXL Type-3 device	     .
 Sizes are in KiB (1024 bytes).
</dd>
<dt>GPUVendor, GPUModel (GPU or Co-Processor OS devices)</dt>
<dd>The vendor and model names of the GPU device.
</dd>
<dt>OpenCLDeviceType, OpenCLPlatformIndex,</dt>
<dt>OpenCLPlatformName, OpenCLPlatformDeviceIndex (OpenCL OS devices)</dt>
<dd>The type of OpenCL device,
 the OpenCL platform index and name,
 and the index of the device within the platform.
</dd>
<dt>OpenCLComputeUnits, OpenCLGlobalMemorySize (OpenCL OS devices)</dt>
<dd>The number of compute units and global memory size of an OpenCL device.
 Sizes are in KiB (1024 bytes).
</dd>
<dt>LevelZeroVendor, LevelZeroModel, LevelZeroBrand,</dt>
<dt>LevelZeroSerialNumber, LevelZeroBoardNumber (LevelZero OS devices)</dt>
<dd>
 The name of the vendor, device model, brand of a Level Zero device,
 and its serial and board numbers.
</dd>
<dt>LevelZeroDriverIndex, LevelZeroDriverDeviceIndex (LevelZero OS devices)</dt>
<dd>The index of the Level Zero driver within the list of drivers,
 and the index of the device within the list of devices managed by this driver.
</dd>
<dt>LevelZeroUUID (LevelZero OS devices or subdevices)</dt>
<dd>The UUID of the device or subdevice.
</dd>
<dt>LevelZeroSubdevices (LevelZero OS devices)</dt>
<dd>The number of subdevices below this OS device.
</dd>
<dt>LevelZeroSubdeviceID (LevelZero OS subdevices)</dt>
<dd>The index of this subdevice within its parent.
</dd>
<dt>LevelZeroDeviceType (LevelZero OS devices or subdevices)</dt>
<dd>A string describing the type of device, for instance "GPU", "CPU", "FPGA", etc.
</dd>
<dt>LevelZeroNumSlices, LevelZeroNumSubslicesPerSlice,</dt>
<dt>LevelZeroNumEUsPerSubslice, LevelZeroNumThreadsPerEU (LevelZero OS devices or subdevices)</dt>
<dd>The number of slices in the device, of subslices per slice,
 of execution units (EU) per subslice, and of threads per EU.
</dd>
<dt>LevelZeroHBMSize, LevelZeroDDRSize, LevelZeroMemorySize (LevelZero OS devices or subdevices)</dt>
<dd>The amount of HBM or DDR memory of a LevelZero device or subdevice.
 Sizes are in KiB (1024 bytes).
 If the type of memory could not be determined, the generic name LevelZeroMemorySize is used.
 For devices that contain subdevices, the amount reported in the root device
 includes the memories of all its subdevices.
</dd>
<dt>LevelZeroCQGroups, LevelZeroCQGroup2 (LevelZero OS devices or subdevices)</dt>
<dd>The number of completion queue groups, and the description of the third group
(as <tt>N*0xX</tt> where <tt>N</tt> is the number of queues in the group,
 and <tt>0xX</tt> is the hexadecimal bitmask of <tt>ze_command_queue_group_property_flag_t</tt>
 listing properties of those queues).
</dd>
<dt>AMDUUID, AMDSerial (RSMI GPU OS devices)</dt>
<dd>The UUID and serial number of AMD GPUs.
</dd>
<dt>RSMIVRAMSize, RSMIVisibleVRAMSize, RSMIGTTSize (RSMI GPU OS devices)</dt>
<dd>
 The amount of GPU memory (VRAM),
 of GPU memory that is visible from the host (Visible VRAM),
 and of system memory that is usable by the GPU (Graphics Translation Table).
 Sizes are in KiB (1024 bytes).
</dd>
<dt>XGMIHiveID (RSMI GPU OS devices)</dt>
<dd>The ID of the group of GPUs (Hive) interconnected by XGMI links
</dd>
<dt>XGMIPeers (RSMI GPU OS devices)</dt>
<dd>The list of RSMI OS devices that are directly connected
  to the current device through XGMI links.
  They are given as a space-separated list of object names,
  for instance <em>rsmi2 rsmi3</em>.
</dd>
<dt>NVIDIAUUID, NVIDIASerial (NVML GPU OS devices)</dt>
<dd>The UUID and serial number of NVIDIA GPUs.
</dd>
<dt>CUDAMultiProcessors, CUDACoresPerMP,</dt>
<dt>CUDAGlobalMemorySize, CUDAL2CacheSize, CUDASharedMemorySizePerMP (CUDA OS devices)</dt>
<dd>
 The number of shared multiprocessors, the number of cores per
 multiprocessor, the global memory size, the (global) L2 cache size,
 and size of the shared memory in each multiprocessor of a CUDA device.
 Sizes are in KiB (1024 bytes).
</dd>
<dt>VectorEngineModel, VectorEngineSerialNumber (VectorEngine OS devices)</dt>
<dd>
 The model and serial number of a VectorEngine device.
</dd>
<dt>VectorEngineCores, VectorEngineMemorySize, VectorEngineLLCSize,</dt>
<dt>VectorEngineL2Size, VectorEngineL1dSize, VectorEngineL1iSize (VectorEngine OS devices)</dt>
<dd>
 The number of cores, memory size, and the sizes of the (global)
 last level cache and of L2, L1d and L1i caches of a VectorEngine device.
 Sizes are in KiB (1024 bytes).
</dd>
<dt>VectorEngineNUMAPartitioned (VectorEngine OS devices)</dt>
<dd>
 If this attribute exists, the VectorEngine device is configured in
 partitioned mode with multiple NUMA nodes.
</dd>
<dt>Address, Port (Network interface OS devices)</dt>
<dd>The MAC address and the port number of a software network
interface, such as <tt>eth4</tt> on Linux.
</dd>
<dt>NodeGUID, SysImageGUID, Port1State, Port2LID, Port2LMC, Port3GID1
(OpenFabrics OS devices)</dt>
<dd>The node GUID and GUID mask,
the state of a port #1 (value is 4 when active),
the LID and LID mask count of port #2,
and GID #1 of port #3.
</dd>
<dt>BXIUUID (OpenFabrics BXI OS devices)</dt>
<dd>The UUID of an Atos/Bull BXI HCA.
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_otherobjs">
\endhtmlonly
\subsection attributes_info_otherobjs Other Object-specific Information

These info attributes are attached to objects specified in parentheses.

<dl>
<dt>DAXDevice (NUMA Nodes)</dt>
<dd>The name of the Linux DAX device that was used to expose a non-volatile
memory region as a volatile NUMA node.
</dd>
<dt>DAXType (NUMA Nodes or DAX OS devices)</dt>
<dd>The type of memory exposed in a Linux DAX device or in the corresponding NUMA node,
either "NVM" (non-volatile memory) or "SPM" (specific-purpose memory).
</dd>
<dt>DAXParent (NUMA Nodes or DAX OS devices)</dt>
<dd>
A string describing the Linux sysfs hierarchy that exposes the DAX device,
for instance containing "hmem1" for specific-purpose memory or "ndbus0" for NVDIMMs.
</dd>
<dt>
<dt>PCIBusID (GPUMemory NUMA Nodes)</dt>
<dd>The PCI bus ID of the GPU whose memory is exposed in this NUMA node.
</dd>
<dt>Inclusive (Caches)</dt>
<dd>The inclusiveness of a cache (1 if inclusive, 0 otherwise).
Currently only available on x86 processors.
</dd>
<dt>SolarisProcessorGroup (Group)</dt>
<dd>
The Solaris kstat processor group name that was used to build this Group object.
</dd>
<dt>PCIVendor, PCIDevice (PCI devices and bridges)</dt>
<dd>The vendor and device names of the PCI device.
</dd>
<dt>PCISlot (PCI devices or Bridges)</dt>
<dd>The name/number of the physical slot where the device is plugged.
 If the physical device contains PCI bridges above the actual PCI device,
 the attribute may be attached to the highest bridge
 (i.e. the first object that actually appears below the physical slot).
</dd>
<dt>Vendor, AssetTag, PartNumber, DeviceLocation, BankLocation (MemoryModule Misc objects)</dt>
<dd>
Information about memory modules (DIMMs) extracted from SMBIOS.
</dd>
</dl>


\htmlonly
</div><div class="subsection" id="attributes_info_user">
\endhtmlonly
\subsection attributes_info_user User-Given Information

Here is a non-exhaustive list of user-provided info attributes
that have a special meaning:
<dl>
<dt>lstopoStyle</dt>
<dd>Enforces the style of an object (background and text colors)
 in the graphical output of lstopo.
 See CUSTOM COLORS in the lstopo(1) manpage for details.
</dd>
</dl>




\page topoattrs Topology Attributes: Distances, Memory Attributes and CPU Kinds

\htmlonly
<div class="section">
\endhtmlonly

Besides the hierarchy of objects and individual object attributes
(see \ref attributes), hwloc may also expose finer information about
the hardware organization.


\htmlonly
</div><div class="section" id="topoattrs_distances">
\endhtmlonly
\section topoattrs_distances Distances

A machine with 4 CPUs may have identical links between every pairs of CPUs,
or those CPUs could also only be connected through a ring.
In the ring case, accessing the memory of nearby CPUs is slower than local
memory, but it is also faster than accessing the memory of CPU on the
opposite side of the ring.
These deep details cannot be exposed in the hwloc hierarchy,
that is why hwloc also exposes distances.

Distances are matrices of values between sets of objects,
usually latencies or bandwidths.
By default, hwloc tries to get a matrix of relative latencies
between NUMA nodes when exposed by the hardware.

In the aforementioned ring case, the matrix could report 10
for latency between a NUMA node and itself, 20 for nearby nodes,
and 30 for nodes that are opposites on the ring.
Those are theoretical values exposed by hardware vendors
(in the System Locality Distance Information Table (SLIT) in the ACPI)
rather than physical latencies.
They are mostly meant for comparing node relative distances.

Distances structures currently created by hwloc are:
<dl>
<dt>NUMALatency (Linux, Solaris, FreeBSD)</dt>
<dd>This is the matrix of theoretical latencies described above.
</dd>
<dt>XGMIBandwidth (RSMI)</dt>
<dd>This is the matrix of unidirectional XGMI bandwidths between
AMD GPUs (in MB/s).
It contains 0 when there is no direct XGMI link between objects.
Values on the diagonal are artificially set to very high so
that local access always appears faster than remote access.

GPUs are identified by RSMI OS devices such as "rsmi0".
They may be converted into the corresponding OpenCL or PCI devices
using hwloc_get_obj_with_same_locality() or the hwloc-annotate tool.

hwloc_distances_transform() or hwloc-annotate may also be used
to transform this matrix into something more convenient,
for instance by replacing bandwidths with numbers of links between peers.
</dt>
<dt>XGMIHops (RSMI)</dt>
<dd>This matrix lists the number of XGMI hops between AMD GPUs.
It reports 1 when there is a direct link between two distinct GPUs.
If there is no XGMI route between them, the value is 0.
The number of hops between a GPU and itself (on the diagonal) is 0 as well.
</dd>
<dt>XeLinkBandwidth (LevelZero)</dt>
<dd>This is the matrix of unidirectional XeLink bandwidths between
Intel GPUs (in MB/s).
It contains 0 when there is no direct XeLink between objects.
When there are multiple links, their bandwidth is aggregated.

Values on the diagonal are artificially set to very high so
that local access always appears faster than remote access.
This includes bandwidths between a (sub)device and itself,
between a subdevice and its parent device,
or between two subdevices of the same parent.

The matrix interconnects all LevelZero devices and subdevices (if any),
even if some of them may have no link at all.
</dd>
<dt>NVLinkBandwidth (NVML)</dt>
<dd>This is the matrix of unidirectional NVLink bandwidths between
NVIDIA GPUs (in MB/s).
It contains 0 when there is no direct NVLink between objects.
When there are multiple links, their bandwidth is aggregated.
Values on the diagonal are artificially set to very high so
that local access always appears faster than remote access.

On POWER platforms, NVLinks may also connects GPUs to CPUs.
On NVIDIA platforms such as DGX-2, a NVSwitch may interconnect GPUs through NVLinks.
In these cases, the distances structure is heterogeneous.
GPUs always appear first in the matrix (as NVML OS devices such as "nvml0"),
and non-GPU objects may appear at the end (Package for POWER processors,
PCI device for NVSwitch).

NVML OS devices may be converted into the corresponding CUDA, OpenCL or PCI devices
using hwloc_get_obj_with_same_locality() or the hwloc-annotate tool.

hwloc_distances_transform() or hwloc-annotate may also be used
to transform this matrix into something more convenient,
for instance by removing switches or CPU ports,
or by replacing bandwidths with numbers of links between peers.

When a NVSwitch interconnects GPUs, only links between one GPU and
different NVSwitch ports are reported. They may be merged into a single
switch port with hwloc_distances_transform() or hwloc-annotate.
Or a transitive closure may also be applied to report the bandwidth
between GPUs across the NVSwitch.
</dl>

Users may also specify their own matrices between any set of objects,
even if these objects are of different types (e.g. bandwidths between GPUs and CPUs).

The entire API is located in hwloc/distances.h.
See also \ref hwlocality_distances_get,
as well as \ref hwlocality_distances_consult
and \ref hwlocality_distances_add.


\htmlonly
</div><div class="section" id="topoattrs_memattrs">
\endhtmlonly
\section topoattrs_memattrs Memory Attributes

Machines with heterogeneous memory, for instance high-bandwidth memory (HBM),
normal memory (DDR), and/or high-capacity slow memory (such as non-volatile
memory DIMMs, NVDIMMs) require applications to allocate buffers
in the appropriate target memory depending on performance and capacity needs.
Those target nodes may be exposed in the hwloc hierarchy as different
memory children but there is a need for performance information to select
the appropriate one.

hwloc memory attributes are designed to expose memory
information such as latency, bandwidth, etc.
Users may also specify their own attributes and values.

The memory attributes API is located in hwloc/memattrs.h,
see \ref hwlocality_memattrs and \ref hwlocality_memattrs_manage for details.
See also an example in doc/examples/memory-attributes.c in the source tree.


\htmlonly
</div><div class="section" id="topoattrs_cpukinds">
\endhtmlonly
\section topoattrs_cpukinds CPU Kinds

Hybrid CPUs may contain different kinds of cores.
The CPU kinds API in hwloc/cpukinds.h provides a way to list the sets
of PUs in each kind and get some optional information about their
hardware characteristics and efficiency.

If the operating system provides efficiency information
(e.g. Windows 10, MacOS X / Darwin and some Linux kernels),
it is used to rank hwloc CPU kinds by efficiency.
Otherwise, hwloc implements several heuristics based on frequencies
and core types (see HWLOC_CPUKINDS_RANKING in \ref envvar).

The ranking shows energy-efficient CPUs first, and high-performance
power-hungry cores last.

These CPU kinds may be annotated with the following native attributes:
<dl>
<dt>FrequencyMaxMHz (Linux)</dt>
<dd>The maximal operating frequency of the core,
as reported by <tt>cpufreq</tt> drivers on Linux.
</dd>
<dt>FrequencyBaseMHz (Linux)</dt>
<dd>The base operating frequency of the core,
as reported by some <tt>cpufreq</tt> drivers on Linux (e.g. <tt>intel_pstate</tt>).
</dd>
<dt>CoreType (x86)</dt>
<dd>A string describing the kind of core,
currently <tt>IntelAtom</tt> or <tt>IntelCore</tt>,
as reported by the x86 CPUID instruction on some Intel processors.
</dd>
<dt>LinuxCapacity (Linux)</dt>
<dd>The Linux-specific CPU capacity found in sysfs,
as reported by the Linux kernel on some recent platforms.
Higher values usually mean that the Linux scheduler considers
the core as high-performance rather than energy-efficient.
</dd>
<dt>LinuxCPUType (Linux)</dt>
<dd>The Linux-specific CPU type found in sysfs,
such as <tt>intel_atom_0</tt>,
as reported by future Linux kernels on some Intel processors.
</dd>
<dt>DarwinCompatible (Darwin / Mac OS X)</dt>
<dd>The compatibility attribute of the CPUs as found
in the IO registry on Darwin / Mac OS X.
For instance <tt>apple,icestorm;ARM,v8</tt> for energy-efficient cores
and <tt>apple,firestorm;ARM,v8</tt> on performance cores on Apple M1 CPU.
</dd>
</dl>

See \ref hwlocality_cpukinds for details.




\page xml Importing and exporting topologies from/to XML files

\htmlonly
<div class="section">
\endhtmlonly

hwloc offers the ability to export topologies to XML files and reload
them later. This is for instance useful for loading topologies faster
(see \ref faq_xml), manipulating other nodes' topology, or avoiding
the need for privileged processes (see \ref faq_privileged).

Topologies may be exported to XML files thanks to hwloc_topology_export_xml(),
or to a XML memory buffer with hwloc_topology_export_xmlbuffer().
The lstopo program can also serve as a XML topology export tool.

XML topologies may then be reloaded later with hwloc_topology_set_xml()
and hwloc_topology_set_xmlbuffer().
The HWLOC_XMLFILE environment variable also tells hwloc to load the topology
from the given XML file (see \ref envvar).

\note Loading XML topologies disables binding because the loaded
topology may not correspond to the physical machine that loads it.
This behavior may be reverted by asserting that loaded file really
matches the underlying system with the HWLOC_THISSYSTEM environment
variable or the ::HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM topology flag.

\note The topology flag ::HWLOC_TOPOLOGY_FLAG_THISSYSTEM_ALLOWED_RESOURCES
may be used to load a XML topology that contains the entire machine
and restrict it to the part that is actually available to the current
process (e.g. when Linux Cgroup/Cpuset are used to restrict the set
of resources).

\note hwloc also offers the ability to export/import \ref hwlocality_diff.

\note XML topology files are not localized. They use a dot as a
decimal separator. Therefore any exported topology can be
reloaded on any other machine without requiring to change the
locale.

\note XML exports contain all details about the platform. It means
that two very similar nodes still have different XML exports
(e.g. some serial numbers or MAC addresses are different).
If a less precise exporting/importing is required, one may want to
look at \ref synthetic instead.


\htmlonly
</div><div class="section" id="xml_backends">
\endhtmlonly
\section xml_backends libxml2 and minimalistic XML backends

hwloc offers two backends for importing/exporting XML.

First, it can use the libxml2 library for importing/exporting XML
files. It features full XML support, for instance when those files
have to be manipulated by non-hwloc software (e.g. a XSLT parser).
The libxml2 backend is enabled by default if libxml2 development
headers are available (the relevant development package is usually
<tt>libxml2-devel</tt> or <tt>libxml2-dev</tt>).

If libxml2 is not available at configure time,
or if <tt>\--disable-libxml2</tt> is passed, hwloc falls back to a
custom backend.
Contrary to the aforementioned full XML backend with libxml2, this
minimalistic XML backend cannot be guaranteed to work with external
programs.
It should only be assumed to be compatible with the same hwloc
release (even if using the libxml2 backend).
Its advantage is, however, to always be available without requiring
any external dependency.

If libxml2 is available but the core hwloc library should not directly
depend on it, the libxml2 support may be built as a dynamicall-loaded
plugin.
One should pass <tt>\--enable-plugins</tt> to enable plugin support
(when supported) and build as plugins all component that support it.
Or pass <tt>\--enable-plugins=xml_libxml</tt> to only build this
libxml2 support as a plugin.


\htmlonly
</div><div class="section" id="xml_errors">
\endhtmlonly
\section xml_errors XML import error management

Importing XML files can fail at least because of file access errors,
invalid XML syntax, non-hwloc-valid XML contents,
or incompatibilities between hwloc releases (see \ref faq_version_xml).

Both backend cannot detect all these errors when the input XML
file or buffer is selected (when hwloc_topology_set_xml() or
hwloc_topology_set_xmlbuffer() is called).
Some errors such non-hwloc-valid contents can only be detected
later when loading the topology with hwloc_topology_load().

It is therefore strongly recommended to check the return value of
both hwloc_topology_set_xml() (or hwloc_topology_set_xmlbuffer())
and hwloc_topology_load() to handle all these errors.




\page synthetic Synthetic topologies

\htmlonly
<div class="section">
\endhtmlonly

hwloc may load fake or remote topologies so as to consult them
without having the underlying hardware available.
Aside from loading XML topologies, hwloc also enables the building of
<em>synthetic</em> topologies that are described by a single string
listing the arity of each levels.

For instance, lstopo may create a topology made of 2 packages,
containing a single NUMA node and a L2 cache above two
single-threaded cores:

\verbatim
$ lstopo -i "pack:2 node:1 l2:1 core:2 pu:1" -
Machine (2048MB)
  Package L#0
    NUMANode L#0 (P#0 1024MB)
    L2 L#0 (4096KB)
      Core L#0 + PU L#0 (P#0)
      Core L#1 + PU L#1 (P#1)
  Package L#1
    NUMANode L#1 (P#1 1024MB)
    L2 L#1 (4096KB)
      Core L#2 + PU L#2 (P#2)
      Core L#3 + PU L#3 (P#3)
\endverbatim

Replacing <tt>-</tt> with <tt>file.xml</tt> in this command line
will export this topology to XML as usual.

\note Synthetic topologies offer a very basic way to export a
topology and reimport it on another machine. It is a lot less
precise than XML but may still be enough when only the hierarchy
of resources matters.


\htmlonly
</div><div class="section" id="synthetic_string">
\endhtmlonly
\section synthetic_string Synthetic description string

Each item in the description string gives the type of the level and
the number of such children under each object of the previous level.
That is why the above topology contains 4 cores (2 cores times 2 nodes).

These type names must be written as
<tt>numanode</tt>, <tt>package</tt>, <tt>core</tt>,
<tt>l2u</tt>, <tt>l1i</tt>, <tt>pu</tt>, <tt>group</tt>
(hwloc_obj_type_sscanf() is used for parsing the type names).
They do not need to be written case-sensitively, nor entirely
(as long as there is no ambiguity, 2 characters such as <tt>ma</tt>
 select a Machine level).
Note that I/O and Misc objects are not available.

Instead of specifying the type of each level, it is possible to
just specify the arities and let hwloc choose all types
according to usual topologies. The following examples are therefore
equivalent:
\verbatim
$ lstopo -i "2 3 4 5 6"
$ lstopo -i "Package:2 NUMANode:3 L2Cache:4 Core:5 PU:6"
\endverbatim

NUMA nodes are handled in a special way since they are not part of the
main CPU hierarchy but rather attached below it as memory children.
Thus, <tt>NUMANode:3</tt> actually means <tt>Group:3</tt> where one
NUMA node is attached below each group.
These groups are merged back into the parent when possible
(typically when a single NUMA node is requested below each parent).

It is also possible the explicitly attach NUMA nodes to specific levels.
For instance, a topology similar to a Intel Xeon Phi processor
(with 2 NUMA nodes per 16-core group) may be created with:
\verbatim
$ lstopo -i "package:1 group:4 [numa] [numa] core:16 pu:4"
\endverbatim

The root object does not appear in the synthetic description string
since it is always a Machine object.
Therefore the Machine type is disallowed in the description as well.

A NUMA level (with a single NUMA node) is automatically added if needed.

Each item may be followed parentheses containing a list of
space-separated attributes. For instance:
<ul>
<li>
 <tt>L2iCache:2(size=32kB)</tt> specifies 2 children
 of 32kB level-2 instruction caches.
 The size may be specified in bytes (without any unit suffix) or as kB, KiB, MB, MiB, etc.
</li>
<li>
 <tt>NUMANode:3(memory=16MB)</tt> specifies 3 NUMA nodes with 16MB each.
 The size may be specified in bytes (without any unit suffix) or as GB, GiB, TB, TiB, etc.
</li>
<li>
 <tt>PU:2(indexes=0,2,1,3)</tt> specifies 2 PU children and the
 full list of OS indexes among the entire set of 4 PU objects.
</li>
<li>
 <tt>PU:2(indexes=numa:core)</tt> specifies 2 PU children whose
 OS indexes are interleaved by NUMA node first and then by package.
</li>
<li>
 Attributes in parentheses at the very beginning of the description
 apply to the root object.
</li>
</ul>

hwloc command-line tools may modify a synthetic topology,
for instance to customize object attributes,
or to remove some objects to make the topology heterogeneous or asymmetric.
See many examples in \ref faq_create_asymmetric.


\htmlonly
</div><div class="section" id="synthetic_use">
\endhtmlonly
\section synthetic_use Loading a synthetic topology

Aside from lstopo, the hwloc programming interface offers the same
ability by passing the synthetic description string to
hwloc_topology_set_synthetic() before hwloc_topology_load().

Synthetic topologies are created by the <tt>synthetic</tt> component.
This component may be enabled by force by setting the HWLOC_SYNTHETIC
environment variable to something such as
<tt>node:2 core:3 pu:4</tt>.

Loading a synthetic topology disables binding support since the
topology usually does not match the underlying hardware.
Binding may be reenabled as usual by setting HWLOC_THISSYSTEM=1 in the
environment or by setting the ::HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM
topology flag.


\htmlonly
</div><div class="section" id="synthetic_export">
\endhtmlonly
\section synthetic_export Exporting a topology as a synthetic string

The function hwloc_topology_export_synthetic() may export
a topology as a synthetic string.
It offers a convenient way to quickly describe the contents of a machine.
The lstopo tool may also perform such an export by forcing the output format.

\verbatim
$ lstopo --of synthetic --no-io
Package:1 L3Cache:1 L2Cache:2 L1dCache:1 L1iCache:1 Core:1 PU:2
\endverbatim

The exported string may be passed back to hwloc for recreating
another similar topology (see also \ref faq_version_synthetic).
The entire tree will be similar, but some attributes such as
the processor model will be missing.

Such an export is only possible if the topology is totally symmetric.
It means that the <tt>symmetric_subtree</tt> field of the root object
is set.
Also memory children should be attached in a symmetric way
(e.g. the same number of memory children below each Package object, etc.).
However, I/O devices and Misc objects are ignored when looking at
symmetry and exporting the string.




\page interoperability Interoperability With Other Software

\htmlonly
<div class="section">
\endhtmlonly

Although hwloc offers its own portable interface, it still may have to
interoperate with specific or non-portable libraries that manipulate
similar kinds of objects.  hwloc therefore offers several specific
"helpers" to assist converting between those specific interfaces and
hwloc.

Some external libraries may be specific to a particular OS; others may
not always be available.  The hwloc core therefore generally does not
explicitly depend on these types of libraries.  However, when a custom
application uses or otherwise depends on such a library, it may
optionally include the corresponding hwloc helper to extend the hwloc
interface with dedicated helpers.

Most of these helpers use structures that are specific to these external
libraries and only meaningful on the local machine. If so, the helper
requires the input topology to match the current machine.
Some helpers also require I/O device discovery to be supported and
enabled for the current topology.

<dl>

<dt>Linux specific features</dt>
 <dd>
  hwloc/linux.h offers Linux-specific helpers that utilize some
  non-portable features of the Linux system, such as binding threads
  through their thread ID ("tid") or parsing kernel CPU mask files.
  See \ref hwlocality_linux.
 </dd>

<dt>Windows specific features</dt>
 <dd>
  hwloc/windows.h offers Windows-specific helpers to query information
  about Windows processor groups.
  See \ref hwlocality_windows.
 </dd>

<dt>Linux libnuma</dt>
 <dd>
  hwloc/linux-libnuma.h provides conversion helpers between hwloc CPU
  sets and libnuma-specific types, such as  bitmasks.  It
  helps you use libnuma memory-binding functions with hwloc CPU sets.
  See \ref hwlocality_linux_libnuma_bitmask and \ref hwlocality_linux_libnuma_ulongs.
 </dd>

<dt>Glibc</dt>
 <dd>
  hwloc/glibc-sched.h offers conversion routines between Glibc and
  hwloc CPU sets in order to use hwloc with functions such as
  sched_getaffinity() or pthread_attr_setaffinity_np().
  See \ref hwlocality_glibc_sched.
 </dd>

<dt>OpenFabrics Verbs</dt>
 <dd>
  hwloc/openfabrics-verbs.h helps interoperability with the
  OpenFabrics Verbs interface.  For example, it can return a list of
  processors near an OpenFabrics device.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_openfabrics.
 </dd>

<dt>OpenCL</dt>
 <dd>
  hwloc/opencl.h enables interoperability with the OpenCL interface.
  Only the AMD and NVIDIA implementations currently offer locality information.
  It may return the list of processors near a GPU given as
  a <tt>cl_device_id</tt>.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_opencl.
 </dd>

<dt>oneAPI Level Zero</dt>
 <dd>
  hwloc/levelzero.h enables interoperability with the oneAPI Level Zero interface.
  It may return the list of processors near an accelerator or GPU.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_levelzero.
 </dd>

<dt>AMD ROCm SMI Library (RSMI)</dt>
 <dd>
  hwloc/rsmi.h enables interoperability with the AMD ROCm SMI interface.
  It may return the list of processors near an AMD GPU.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_rsmi.
 </dd>

<dt>NVIDIA CUDA</dt>
 <dd>
  hwloc/cuda.h and hwloc/cudart.h enable interoperability with
  NVIDIA CUDA Driver and Runtime interfaces. For instance, it may
  return the list of processors near NVIDIA GPUs.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_cuda and \ref hwlocality_cudart.
 </dd>

<dt>NVIDIA Management Library (NVML)</dt>
 <dd>
  hwloc/nvml.h enables interoperability with the NVIDIA NVML interface.
  It may return the list of processors near a NVIDIA GPU given as
  a <tt>nvmlDevice_t</tt>.
  It may also return the corresponding OS device hwloc object for further
  information (if I/O device discovery is enabled).
  See \ref hwlocality_nvml.
 </dd>

<dt>NVIDIA displays</dt>
 <dd>
  hwloc/gl.h enables interoperability with NVIDIA displays
  using the NV-CONTROL X extension (NVCtrl library).
  If I/O device discovery is enabled, it may return the OS device
  hwloc object that corresponds to a display
  given as a name such as <em>:0.0</em>
  or given as a port/device pair (server/screen).
  See \ref hwlocality_gl.
 </dd>

<dt>Taskset command-line tool</dt>
 <dd>
  The taskset command-line tool is widely used for binding
  processes. It manipulates CPU set strings in a format that
  is slightly different from hwloc's one (it does not divide the
  string in fixed-size subsets and separates them with commas).
  To ease interoperability, hwloc offers routines to convert
  hwloc CPU sets from/to taskset-specific string format.
  See for instance hwloc_bitmap_taskset_snprintf() in
  \ref hwlocality_bitmap().

  Most hwloc command-line tools also support the <tt>\--taskset</tt>
  option to manipulate taskset-specific strings.
 </dd>

</dl>



\page threadsafety Thread Safety

\htmlonly
<div class="section">
\endhtmlonly

Like most libraries that mainly fill data structures, hwloc is not
thread safe but rather reentrant: all state is held in a
::hwloc_topology_t instance without mutex protection.  That means, for
example, that two threads can safely operate on and modify two
different ::hwloc_topology_t instances, but they should not
simultaneously invoke functions that modify the <em>same</em>
instance.  Similarly, one thread should not modify a
::hwloc_topology_t instance while another thread is reading or
traversing it.  However, two threads can safely read or traverse the
same ::hwloc_topology_t instance concurrently.

When running in multiprocessor environments, be aware that proper thread
synchronization and/or memory coherency protection is needed to pass hwloc
data (such as ::hwloc_topology_t pointers) from one processor
to another (e.g., a mutex, semaphore, or a memory barrier).
Note that this is not a hwloc-specific requirement, but it is worth
mentioning.

For reference, ::hwloc_topology_t modification operations include
(but may not be limited to):

<dl>

<dt>Creation and destruction</dt>
  <dd><tt>hwloc_topology_init(), hwloc_topology_load(),
  hwloc_topology_destroy()</tt> (see \ref hwlocality_creation) imply
  major modifications of the structure, including freeing some
  objects.  No other thread cannot access the topology or any of its
  objects at the same time.

  Also references to objects inside the topology are not valid anymore
  after these functions return.  </dd>

<dt>Runtime topology modifications</dt>
  <dd><tt>hwloc_topology_insert_misc_object()</tt>,
  <tt>hwloc_topology_alloc_group_object()</tt>,
  and <tt>hwloc_topology_insert_group_object()</tt>
  (see \ref hwlocality_tinker) may modify the topology significantly by adding
  objects inside the tree, changing the topology depth, etc.

  <tt>hwloc_distances_add_commit()</tt> and <tt>hwloc_distances_remove()</tt>
  (see \ref hwlocality_distances_add) modify the list of distance structures
  in the topology, and the former may even insert new Group objects.

  <tt>hwloc_memattr_register()</tt> and <tt>hwloc_memattr_set_value()</tt>
  (see \ref hwlocality_memattrs_manage) modify the memory attributes
  of the topology.

  <tt>hwloc_topology_restrict()</tt> modifies the topology even more
  dramatically by removing some objects.

  <tt>hwloc_topology_refresh()</tt> updates some internal cached structures.
  (see below).

  Although references to former objects <em>may</em> still be valid
  after insertion or restriction, it is strongly advised to not rely on any such
  guarantee and always re-consult the topology to reacquire new
  instances of objects.  </dd>

<dt>Consulting distances</dt>
  <dd>
  <tt>hwloc_distances_get()</tt> and its variants are thread-safe
  except if the topology was recently modified
  (because distances may involve objects that were removed).

  Whenever the topology is modified (see above), <tt>hwloc_topology_refresh()</tt>
  should be called in the same thread-safe context to force the refresh
  of internal distances structures.
  A call to <tt>hwloc_distances_get()</tt> may also refresh
  distances-related structures.

  Once this refresh has been performed, multiple <tt>hwloc_distances_get()</tt>
  may then be performed concurrently by multiple threads.
  </dd>

<dt>Consulting memory attributes</dt>
  <dd>
  Functions consulting memory attributes in hwloc/memattrs.h
  are thread-safe except if the topology was recently modified
  (because memory attributes may involve objects that were removed).

  Whenever the topology is modified (see above), <tt>hwloc_topology_refresh()</tt>
  should be called in the same thread-safe context to force the refresh
  of internal memory attribute structures.
  A call to <tt>hwloc_memattr_get_value()</tt> or
  <tt>hwloc_memattr_get_targets()</tt> may also refresh internal
  structures for a given memory attribute.

  Once this refresh has been performed, multiple functions consulting
  memory attributes may then be performed concurrently by multiple threads.
  </dd>

<dt>Locating topologies</dt>

  <dd><tt>hwloc_topology_set_*</tt>
  (see \ref hwlocality_configuration) do not modify the topology
  directly, but they do modify internal structures describing the
  behavior of the upcoming invocation of <tt>hwloc_topology_load()</tt>.
  Hence, all of these functions should not be used concurrently.
  </dd>

</dl>



\page plugins Components and plugins

\htmlonly
<div class="section">
\endhtmlonly

hwloc is organized in <b>components</b> that are responsible for discovering
objects.
Depending on the topology configuration, some components will be used
(once enabled, they create a <b>backend</b>),
some will be ignored.

The usual default is to enable the native operating system component,
(e.g. <tt>linux</tt> or <tt>solaris</tt>) and the
<tt>pci</tt> one.
If available, an architecture-specific component (such as <tt>x86</tt>)
may also improve the topology detection.
Finally, some hardware-specific components (such as <tt>cuda</tt> or <tt>rsmi</tt>)
may add information about GPUs, accelerators, etc.

If a XML topology is loaded, the <tt>xml</tt> discovery  component
will be used instead of all other components.


\htmlonly
</div><div class="section" id="plugins_default">
\endhtmlonly
\section plugins_default Components enabled by default

The hwloc core contains a list of components sorted by priority.
Each one is enabled as long as it does not conflict with the
previously enabled ones.
This includes native operating system components,
architecture-specific ones, and if available, I/O components
such as <tt>pci</tt>.

Usually the native operating system component
(when it exists, e.g. <tt>linux</tt> or <tt>aix</tt>)
is enabled first.
Then hwloc looks for an architecture specific component
(e.g. <tt>x86</tt>).
Finally there also exist a basic component (<tt>no_os</tt>)
that just tries to discover the number of PUs in the system.

Each component discovers as much topology information as possible.
Most of them, including most native OS components, do nothing
unless the topology is still empty.
Some others, such as <tt>x86</tt> and <tt>pci</tt>,
can complete and annotate what other backends found earlier.
Discovery is performed by phases: CPUs are first discovered,
then memory is attached, then PCI, etc.

Default priorities ensure that clever components are invoked first.
Native operating system components have higher priorities,
and are therefore invoked first, because they likely offer
very detailed topology information.
If needed, it will be later extended by architecture-specific
information (e.g. from the <tt>x86</tt> component).

If any configuration function such as hwloc_topology_set_xml()
is used before loading the topology, the corresponding component
is enabled first.
Then, as usual, hwloc enables any other component (based on
priorities) that does not conflict.

Certain components that manage a virtual topology, for instance XML
topology import or synthetic topology description,
conflict with all other components.
Therefore, they may only be loaded
(e.g. with <tt>hwloc_topology_set_xml()</tt>)
if no other component is enabled.

The environment variable <tt>HWLOC_COMPONENTS_VERBOSE</tt>
may be set to get verbose messages about available components
(including their priority) and enabling as backends.


\htmlonly
</div><div class="section" id="plugins_select">
\endhtmlonly
\section plugins_select Selecting which components to use

If no topology configuration functions such as
<tt>hwloc_topology_set_synthetic()</tt> have been called,
components may be selected with environment variables such as
<tt>HWLOC_XMLFILE</tt>, <tt>HWLOC_SYNTHETIC</tt>,
<tt>HWLOC_FSROOT</tt>, or <tt>HWLOC_CPUID_PATH</tt> (see \ref envvar).

Finally, the environment variable <tt>HWLOC_COMPONENTS</tt>
resets the list of selected components.
If the variable is set and empty (or set to a single comma separating nothing,
since some operating systems do not accept empty variables),
the normal component priority order is used.

If the variable is set to <tt>x86</tt> in this variable will cause
the <tt>x86</tt> component to take precedence over any other component,
including the native operating system component.
It is therefore loaded first, before hwloc tries to load all remaining
non-conflicting components.
In this case, <tt>x86</tt> would take care of discovering everything
it supports, instead of only completing what the native OS information.
This may be useful if the native component is buggy on some platforms.

It is possible to prevent some components from being loaded by prefixing their
name with <tt>-</tt> in the list. For instance <tt>x86,-pci</tt> will load the
<tt>x86</tt> component, then let hwloc load all the usual components except
<tt>pci</tt>.
A single component phase may also be blacklisted, for instance with <tt>-linux:io</tt>.

It is possible to prevent all remaining components from being loaded
by placing <tt>stop</tt> in the environment variable.
Only the components listed before this keyword will be enabled.

hwloc_topology_set_components() may also be used inside the program
to prevent the loading of a specific component (or phases) for the target topology.


\htmlonly
</div><div class="section" id="plugins_load">
\endhtmlonly
\section plugins_load Loading components from plugins

Components may optionally be built as <b>plugins</b> so that the hwloc core
library does not directly depend on their dependencies (for instance
the <tt>libpciaccess</tt> library).
Plugin support may be enabled with the <tt>\--enable-plugins</tt>
configure option.
All components buildable as plugins will then be built as plugins.
The configure option may be given a comma-separated list of component
names to specify the exact list of components to build as plugins.

Plugins are built as independent dynamic libraries that are installed
in <tt>$libdir/hwloc</tt>.
All plugins found in this directory are loaded during
<tt>topology_init()</tt>
(unless blacklisted in <tt>HWLOC_PLUGINS_BLACKLIST</tt>, see \ref envvar).
A specific list of directories (colon-separated) to scan may be
specified in the <tt>HWLOC_PLUGINS_PATH</tt> environment variable.

Note that loading a plugin just means that the corresponding component
is registered to the hwloc core.
Components are then only enabled (as a <b>backend</b>) if the topology configuration
requests it, as explained in the previous sections.

Also note that plugins should carefully be enabled and used when
embedding hwloc in another project, see \ref embed for details.


\htmlonly
</div><div class="section" id="plugins_list">
\endhtmlonly
\section plugins_list Existing components and plugins

All components distributed within hwloc are listed below.
The list of actually available components may be listed
at running with the <tt>HWLOC_COMPONENTS_VERBOSE</tt>
environment variable (see \ref envvar).

<dl>

<dt>linux</dt>
<dd>
 The official component for discovering CPU, memory and I/O devices on Linux.
 It discovers PCI devices without the help of external libraries such as libpciaccess,
 but requires the pci component for adding vendor/device names to PCI objects.
 It also discovers many kinds of Linux-specific OS devices.
</dd>
<dt>aix, darwin, freebsd, hpux, netbsd, solaris, windows</dt>
<dd>
 Each officially supported operating system has its own native component,
 which is statically built when supported, and which is used by default.
</dd>
<dt>x86</dt>
<dd>
 The x86 architecture (either 32 or 64 bits) has its own component
 that may complete or replace the previously-found CPU information.
 It is statically built when supported.
</dd>
<dt>bgq</dt>
<dd>
 This component is specific to IBM BlueGene/Q compute node (running CNK).
 It is built and enabled by default when <tt>\--host=powerpc64-bgq-linux</tt>
 is passed to configure (see \ref faq_bgq).
</dd>
<dt>no_os</dt>
<dd>
 A basic component that just tries to detect the number of processing
 units in the system. It mostly serves on operating systems that are
 not natively supported.
 It is always statically built.
</dd>
<dt>pci</dt>
<dd>
 PCI object discovery uses the external libpciaccess library;
 see \ref iodevices. It may also annotate existing PCI devices with vendor
 and device names.
 <b>It may be built as a plugin</b>.
</dd>
<dt>opencl</dt>
<dd>
 The OpenCL component creates co-processor OS device objects such as
 <em>opencl0d0</em> (first device of the first OpenCL platform)
 or <em>opencl1d3</em> (fourth device of the second platform).
 Only the AMD and NVIDIA OpenCL implementations currently offer locality
 information.
 <b>It may be built as a plugin</b>.
</dd>
<dt>rsmi</dt>
<dd>
 This component creates GPU OS device objects such as
 <em>rsmi0</em> for describing AMD GPUs.
 <b>It may be built as a plugin</b>.
</dd>
<dt>levelzero</dt>
<dd>
 This component creates co-processor OS device objects such as
 <em>ze0</em> for describing oneAPI Level Zero devices.
 It may also create sub-OS-devices such as <em>ze0.0</em> inside those devices.
 <b>It may be built as a plugin</b>.
</dd>
<dt>cuda</dt>
<dd>
 This component creates co-processor OS device objects such as <em>cuda0</em>
 that correspond to NVIDIA GPUs used with CUDA library.
 <b>It may be built as a plugin</b>.
</dd>
<dt>nvml</dt>
<dd>
 Probing the NVIDIA Management Library creates OS device objects
 such as <em>nvml0</em> that are useful for batch schedulers.
 It also detects the actual PCIe link bandwidth without depending
 on power management state and without requiring administrator
 privileges.
 <b>It may be built as a plugin</b>.
</dd>
<dt>gl</dt>
<dd>
 Probing the NV-CONTROL X extension (NVCtrl library) creates OS
 device objects such as <em>:0.0</em> corresponding to NVIDIA
 displays.
 They are useful for graphical applications that need to place
 computation and/or data near a rendering GPU.
 <b>It may be built as a plugin</b>.
</dd>
<dt>synthetic</dt>
<dd>
 Synthetic topology support (see \ref synthetic) is always built statically.
</dd>
<dt>xml</dt>
<dd>
 XML topology import (see \ref xml) is always built statically.
 It internally uses a specific class of components for the actual XML
 import/export routines (see \ref xml_backends for details).
 <ul>
 <li><b>xml_nolibxml</b> is a basic and hwloc-specific XML import/export.
  It is always statically built.
 </li>
 <li><b>xml_libxml</b> relies on the external libxml2 library for
  provinding a feature-complete XML import/export.
  <b>It may be built as a plugin</b>.
 </li>
</dd>
<dt>fake</dt>
<dd>
 A dummy plugin that does nothing but is used for debugging plugin support.
</dd>
</dl>




\page embed Embedding hwloc in Other Software

\htmlonly
<div class="section">
\endhtmlonly

It can be desirable to include hwloc in a larger software package (be
sure to check out the LICENSE file) so that users don't have to
separately download and install it before installing your software.
This can be advantageous to ensure that your software uses a
known-tested/good version of hwloc, or for use on systems that do not
have hwloc pre-installed.

When used in "embedded" mode, hwloc will:

- not install any header files
- not build any documentation files
- not build or install any executables or tests
- not build <tt>libhwloc.*</tt> -- instead, it will build
  <tt>libhwloc_embedded.*</tt>

There are two ways to put hwloc into "embedded" mode.  The first is
directly from the configure command line:

\verbatim
shell$ ./configure --enable-embedded-mode ...
\endverbatim

The second requires that your software project uses the GNU Autoconf /
Automake / Libtool tool chain to build your software.  If you do this,
you can directly integrate hwloc's m4 configure macro into your
configure script.  You can then invoke hwloc's configuration tests and
build setup by calling a m4 macro (see below).

Although hwloc dynamic shared object plugins may be used in embedded
mode, the embedder project will have to manually setup dlopen or libltdl in its
build system so that hwloc can load its plugins at run time.
Also, embedders should be aware of complications that can arise due to
public and private linker namespaces (e.g., if the embedder project is
loaded into a private namespace and then hwloc tries to dynamically
load its plugins, such loading may fail since the hwloc plugins can't
find the hwloc symbols they need).
The embedder project is <b>strongly</b> advised not to use hwloc's
dynamically loading plugins / dlopen / libltdl capability.


\htmlonly
</div><div class="section" id="embedding_m4">
\endhtmlonly
\section embedding_m4 Using hwloc's M4 Embedding Capabilities

Every project is different, and there are many different ways of
integrating hwloc into yours.  What follows is <em>one</em> example of
how to do it.

If your project uses recent versions Autoconf, Automake, and Libtool
to build, you can use hwloc's embedded m4 capabilities.  We have
tested the embedded m4 with projects that use Autoconf 2.65, Automake
1.11.1, and Libtool 2.2.6b.  Slightly earlier versions of may also
work but are untested.  Autoconf versions prior to 2.65 are almost
certain to not work.

You can either copy all the config/hwloc*m4 files from the hwloc
source tree to the directory where your project's m4 files reside, or
you can tell aclocal to find more m4 files in the embedded hwloc's
"config" subdirectory (e.g., add "-Ipath/to/embedded/hwloc/config" to
your Makefile.am's ACLOCAL_AMFLAGS).

The following macros can then be used from your configure script (only
HWLOC_SETUP_CORE <em>must</em> be invoked if using the m4 macros):

- HWLOC_SETUP_CORE(config-dir-prefix, action-upon-success,
  action-upon-failure, print_banner_or_not): Invoke the hwloc
  configuration tests and setup the hwloc tree to build.  The first
  argument is the prefix to use for AC_OUTPUT files -- it's where the
  hwloc tree is located relative to <tt>$top_srcdir</tt>.  Hence, if
  your embedded hwloc is located in the source tree at contrib/hwloc,
  you should pass <tt>[contrib/hwloc]</tt> as the first argument.  If
  HWLOC_SETUP_CORE and the rest of <tt>configure</tt> completes
  successfully, then "make" traversals of the hwloc tree with standard
  Automake targets (all, clean, install, etc.) should behave as
  expected.  For example, it is safe to list the hwloc directory in
  the SUBDIRS of a higher-level Makefile.am.  The last argument, if
  not empty, will cause the macro to display an announcement banner
  that it is starting the hwloc core configuration tests.

  HWLOC_SETUP_CORE will set the following environment variables and
  AC_SUBST them: HWLOC_EMBEDDED_CFLAGS, HWLOC_EMBEDDED_CPPFLAGS, and
  HWLOC_EMBEDDED_LIBS.  These flags are filled with the values
  discovered in the hwloc-specific m4 tests, and can be used in your
  build process as relevant.  The _CFLAGS, _CPPFLAGS, and _LIBS
  variables are necessary to build libhwloc (or libhwloc_embedded)
  itself.  

  HWLOC_SETUP_CORE also sets HWLOC_EMBEDDED_LDADD environment variable
  (and AC_SUBSTs it) to contain the location of the
  libhwloc_embedded.la convenience Libtool archive.  It can be used in
  your build process to link an application or other library against
  the embedded hwloc library.

  <strong>NOTE: If the HWLOC_SET_SYMBOL_PREFIX macro is used, it must
  be invoked <em>before</em> HWLOC_SETUP_CORE.</strong>

- HWLOC_BUILD_STANDALONE: HWLOC_SETUP_CORE defaults to building hwloc
  in an "embedded" mode (described above).  If HWLOC_BUILD_STANDALONE
  is invoked *before* HWLOC_SETUP_CORE, the embedded definitions will
  not apply (e.g., libhwloc.la will be built, not
  libhwloc_embedded.la).

- HWLOC_SET_SYMBOL_PREFIX(foo_): Tells the hwloc to prefix all of
  hwloc's types and public symbols with "foo_"; meaning that function
  hwloc_init() becomes foo_hwloc_init().  Enum values are prefixed
  with an upper-case translation if the prefix supplied;
  HWLOC_OBJ_CORE becomes FOO_hwloc_OBJ_CORE.  This is recommended
  behavior if you are including hwloc in middleware -- it is possible
  that your software will be combined with other software that links
  to another copy of hwloc.  If both uses of hwloc utilize different
  symbol prefixes, there will be no type/symbol clashes, and
  everything will compile, link, and run successfully.  If you both
  embed hwloc without changing the symbol prefix and also link against
  an external hwloc, you may get multiple symbol definitions when
  linking your final library or application.

- HWLOC_SETUP_DOCS, HWLOC_SETUP_UTILS, HWLOC_SETUP_TESTS: These three
  macros only apply when hwloc is built in "standalone" mode (i.e.,
  they should NOT be invoked unless HWLOC_BUILD_STANDALONE has already
  been invoked).

- HWLOC_DO_AM_CONDITIONALS: If you embed hwloc in a larger project and
  build it conditionally with Automake (e.g., if HWLOC_SETUP_CORE is
  invoked conditionally), you must unconditionally invoke
  HWLOC_DO_AM_CONDITIONALS to avoid warnings from Automake (for the
  cases where hwloc is not selected to be built).  This macro is
  necessary because hwloc uses some AM_CONDITIONALs to build itself,
  and AM_CONDITIONALs cannot be defined conditionally.  Note that it
  is safe (but unnecessary) to call HWLOC_DO_AM_CONDITIONALS even if
  HWLOC_SETUP_CORE is invoked unconditionally.  If you are not using
  Automake to build hwloc, this macro is unnecessary (and will actually
  cause errors because it invoked AM_* macros that will be undefined).

<strong>NOTE:</strong> When using the HWLOC_SETUP_CORE m4 macro, it may
be necessary to explicitly invoke AC_CANONICAL_TARGET (which requires
config.sub and config.guess) and/or AC_USE_SYSTEM_EXTENSIONS macros
early in the configure script (e.g., after AC_INIT but before
AM_INIT_AUTOMAKE).  See the Autoconf documentation for further
information.

Also note that hwloc's top-level configure.ac script uses exactly the
macros described above to build hwloc in a standalone mode (by
default).  You may want to examine it for one example of how these
macros are used.


\htmlonly
</div><div class="section" id="embedding_example">
\endhtmlonly
\section embedding_example Example Embedding hwloc

Here's an example of integrating with a larger project named sandbox
that already uses Autoconf, Automake, and Libtool to build itself:

\verbatim
# First, cd into the sandbox project source tree
shell$ cd sandbox
shell$ cp -r /somewhere/else/hwloc-<version> my-embedded-hwloc
shell$ edit Makefile.am
  1. Add "-Imy-embedded-hwloc/config" to ACLOCAL_AMFLAGS
  2. Add "my-embedded-hwloc" to SUBDIRS
  3. Add "$(HWLOC_EMBEDDED_LDADD)" and "$(HWLOC_EMBEDDED_LIBS)" to 
     sandbox's executable's LDADD line.  The former is the name of the 
     Libtool convenience library that hwloc will generate.  The latter 
     is any dependent support libraries that may be needed by 
     $(HWLOC_EMBEDDED_LDADD).
  4. Add "$(HWLOC_EMBEDDED_CFLAGS)" to AM_CFLAGS
  5. Add "$(HWLOC_EMBEDDED_CPPFLAGS)" to AM_CPPFLAGS
shell$ edit configure.ac
  1. Add "HWLOC_SET_SYMBOL_PREFIX(sandbox_hwloc_)" line
  2. Add "HWLOC_SETUP_CORE([my-embedded-hwloc], [happy=yes], [happy=no])" line
  3. Add error checking for happy=no case
shell$ edit sandbox.c
  1. Add #include <hwloc.h>
  2. Add calls to sandbox_hwloc_init() and other hwloc API functions
\endverbatim

Now you can bootstrap, configure, build, and run the sandbox as normal
-- all calls to "sandbox_hwloc_*" will use the embedded hwloc rather
than any system-provided copy of hwloc.






\page faq Frequently Asked Questions (FAQ)


\htmlonly
<div class="section" id="faq1">
\endhtmlonly
\section faq1 Concepts


\subsection faq_why I only need binding, or the number of cores, why should I use hwloc ?

hwloc is its portable API that works on a variety of operating
systems.
It supports binding of threads, processes and memory buffers
(see \ref hwlocality_cpubinding and \ref hwlocality_membinding).
Even if some features are not supported on some systems,
using hwloc is much easier than reimplementing your own portability layer.

Moreover, hwloc provides knowledge of cores and hardware threads.
It offers easy ways to bind tasks to individual hardware threads,
or to entire multithreaded cores, etc.
See \ref faq_smt.
Most alternative software for binding do not even know whether each
core is single-threaded, multithreaded or hyper-threaded.
They would bind to individual threads without any way to know whether
multiple tasks are in the same physical core.

However, using hwloc comes with an overhead since a topology must
be loaded before gathering information and binding tasks or memory.
Fortunately this overhead may be significantly reduced by filtering
non-interesting information out of the topology,
see \ref faq_disable_faster below.


\subsection faq_disable_faster What may I disable to make hwloc faster?

Building a hwloc topology on a large machine may be slow because
the discovery of hundreds of hardware cores or threads takes time
(especially when reading thousands of sysfs files on Linux).
Ignoring some objects (for instance caches) that aren't useful
to the current application may improve this overhead.
One should also consider using XML (see \ref faq_xml) to work
around such issues.

Contrary to lstopo which enables most features (see \ref faq_slow_lstopo),
the default hwloc configuration is to keep all objects enabled
except I/Os and instruction caches.
This usually builds a very precise view of the CPU and memory subsystems,
which may be reduced if some information is unneeded.

<br/>
The following code tells hwloc to build a much smaller topology that
only contains Cores (explicitly filtered-in below),
hardware threads (PUs, cannot be filtered-out),
NUMA nodes (cannot be filtered-out),
and the root object (usually a Machine; the root cannot be removed without breaking the tree):

\verbatim
hwloc_topology_t topology;
hwloc_topology_init(&topology);
/* filter everything out */
hwloc_topology_set_all_types_filter(topology, HWLOC_TYPE_FILTER_KEEP_NONE);
/* filter Cores back in */
hwloc_topology_set_type_filter(topology, HWLOC_OBJ_CORE, HWLOC_TYPE_FILTER_KEEP_ALL);
hwloc_topology_load(topology);
\endverbatim

However, one should remember that filtering such objects out removes
locality information from the hwloc tree.
For instance, we may not know anymore which PU is close to which NUMA
node.
This would be useful to applications that explicitly want to
place specific memory buffers close to specific tasks.
To ignore useless objects but keep those that bring locality/hierarchy
information, applications may replace ::HWLOC_TYPE_FILTER_KEEP_NONE
with ::HWLOC_TYPE_FILTER_KEEP_STRUCTURE above.

<br/>
Starting with hwloc 2.8, it is also possible to ignore distances
between objects, memory performance attributes, and kinds of CPU cores,
by setting topology flags before load:
\verbatim
[...]
/* disable distances, memory attributes and CPU kinds */
hwloc_topology_set_flags(topology, HWLOC_TOPOLOGY_FLAG_NO_DISTANCES
                                   |HWLOC_TOPOLOGY_FLAG_NO_MEMATTRS
                                   |HWLOC_TOPOLOGY_FLAG_NO_CPUKINDS);
[...]
hwloc_topology_load(topology);
\endverbatim

<br/>
Finally it is possible to prevent some hwloc components from being
loaded and queried.
If you are sure that the Linux (or x86) component is enough to discover
everything you need, you may ask hwloc to disable all other components
by setting something like <tt>HWLOC_COMPONENTS=linux,stop</tt>
in the environment.
See \ref plugins for details.


\subsection faq_indexes Should I use logical or physical/OS indexes? and how?

One of the original reasons why hwloc was created is that <b>physical/OS indexes</b>
(<tt>obj->os_index</tt>) are often crazy and unpredictable:
processors numbers are usually
non-contiguous (processors 0 and 1 are not physically close), they vary from
one machine to another, and may even change after a BIOS or system update.
These numbers make task placement hardly portable.
Moreover some objects have no physical/OS numbers (caches), and some objects
have non-unique numbers (core numbers are only unique within a socket).
Physical/OS indexes are only guaranteed to exist and be unique for PU
and NUMA nodes.

hwloc therefore introduces <b>logical indexes</b> (<tt>obj->logical_index</tt>)
which are portable, contiguous and logically ordered
(based on the resource organization in the locality tree).
In general, one should only use logical indexes and just let hwloc do the
internal conversion when really needed (when talking to the OS and hardware).

hwloc developers recommends that users do not use physical/OS indexes
unless they really know what they are doing.
The main reason for still using physical/OS indexes is when interacting with
non-hwloc tools such as numactl or taskset, or when reading hardware information
from raw sources such as /proc/cpuinfo.

lstopo options <tt>-l</tt> and <tt>-p</tt> may be used to switch between
logical indexes (prefixed with <tt>L#</tt>) and physical/OS indexes (<tt>P#</tt>).
Converting one into the other may also be achieved with hwloc-calc which may
manipulate either logical or physical indexes as input or output.
See also \ref cli_hwloc_calc.

\verbatim
# Convert PU with physical number 3 into logical number
$ hwloc-calc -I pu --physical-input --logical-output pu:3
5

# Convert a set of NUMA nodes from logical to physical
# (beware that the output order may not match the input order)
$ hwloc-calc -I numa --logical-input --physical-output numa:2-3 numa:7
0,2,5
\endverbatim


\subsection faq_structural hwloc is only a structural model, it ignores performance models, memory bandwidth, etc.?

hwloc is indeed designed to provide applications with a structural model
of the platform. This is an orthogonal approach to describing the
machine with performance models, for instance using memory bandwidth
or latencies measured by benchmarks.
We believe that both approaches are important for helping application
make the most of the hardware.

For instance, on a dual-processor host with four cores each, hwloc
clearly shows which four cores are together.
Latencies between all pairs of cores of the same processor are likely
identical, and also likely lower than the latency between cores of
different processors.
However, the structural model cannot guarantee such implementation
details.
On the other side, performance models would reveal such details
without always clearly identifying which cores are in the same
processor.

The focus of hwloc is mainly of the structural modeling side.
However, hwloc lets user adds performance information to the topology
through distances
(see \ref topoattrs_distances),
memory attributes
(see \ref topoattrs_memattrs)
or even custom annotations (see \ref faq_annotate).
hwloc may also use such distance information for grouping objects
together (see \ref faq_onedim and \ref faq_groups).


\subsection faq_onedim hwloc only has a one-dimensional view of the architecture, it ignores distances?

hwloc places all objects in a tree. Each level is a one-dimensional
view of a set of similar objects. All children of the same object (siblings)
are assumed to be equally interconnected (same distance between any of them),
while the distance between children of different objects (cousins) is supposed
to be larger.

Modern machines exhibit complex hardware interconnects, so this tree
may miss some information about the actual physical distances between objects.
The hwloc topology may therefore be annotated with distance information that
may be used to build a more realistic representation (multi-dimensional)
of each level.
For instance, there can be a distance matrix that representing the latencies
between any pair of NUMA nodes if the BIOS and/or operating system reports them.

For more information about the hwloc distances, see \ref topoattrs_distances.


\subsection faq_groups What are these Group objects in my topology?

hwloc comes with a set of predefined object types (Core, Package, NUMA node, Caches)
that match the vast majority of hardware platforms.
The ::HWLOC_OBJ_GROUP type was designed for cases where this set is not sufficient.
Groups may be used anywhere to add more structure information to the topology,
for instance to show that 2 out of 4 NUMA nodes are actually closer than the others.
When applicable, the <tt>subtype</tt> field describes why a Group
was actually added (see also \ref attributes_normal).

hwloc currently uses Groups for the following reasons:
<ul>
<li>NUMA parents when memory locality does not match any existing object.</li>
<li>I/O parents when I/O locality does not match any existing object.</li>
<li>Distance-based groups made of close objects.</li>
<li>AMD Bulldozer dual-core compute units (<tt>subtype</tt> is <tt>ComputeUnit</tt>, in the x86 backend),
 but these objects are usually merged with the L2 caches.</li>
<li>Intel Extended Topology Enumeration levels (in the x86 backend).</li>
<li>Windows processor groups when HWLOC_WINDOWS_PROCESSOR_GROUP_OBJS=1 is set in the environment
  (except if they contain exactly a single NUMA node, or a single Package, etc.).</li>
<li>IBM S/390 "Books" on Linux (<tt>subtype</tt> is <tt>Book</tt>).</li>
<li>Linux Clusters of CPUs (<tt>subtype</tt> is <tt>Cluster</tt>),
  for instance for ARM cores sharing of some internal cache or bus,
  or x86 cores sharing a L2 cache (since Linux kernel 5.16).
  <tt>HWLOC_DONT_MERGE_CLUSTER_GROUPS=1</tt> may be set in the environment
  to disable the automerging of these groups with identical caches, etc.
</li>
<li>AIX unknown hierarchy levels.</li>
</ul>

hwloc Groups are only kept if no other object has the same
locality information.
It means that a Group containing a single child is merged
into that child.
And a Group is merged into its parent if it is its only child.
For instance a Windows processor group containing a single NUMA node
would be merged with that NUMA node since it already contains the
relevant hierarchy information.

When inserting a custom Group with hwloc_hwloc_topology_insert_group_object(),
this merging may be disabled by setting its <tt>dont_merge</tt> attribute.


\subsection faq_asymmetric What happens if my topology is asymmetric?

hwloc supports asymmetric topologies even if most platforms are usually
symmetric. For example, there could be different types of processors
in a single machine, each with different numbers of cores, symmetric
multithreading, or levels of caches.

In practice, asymmetric topologies are rare but occur for at least two reasons:
<ul>
<li>Intermediate groups may added for I/O affinity:
on a 4-package machine, an I/O bus may be
connected to 2 packages. These packages are below an additional Group
object, while the other packages are not (see also \ref faq_groups).
</li><li>
If only part of a node is available to the current process,
for instance because the resource manager uses Linux Cgroups to restrict
process resources, some cores (or NUMA nodes) will disappear from
the topology (unless flag ::HWLOC_TOPOLOGY_FLAG_INCLUDE_DISALLOWED was passed).
On a 32-core machine where 12 cores were allocated to the process,
this may lead to one CPU package with 8 cores, another one with only 4 cores,
and two missing packages.
</li>
</ul>

To understand how hwloc manages such cases, one should first remember
the meaning of levels and cousin objects. All objects of the same type
are gathered as horizontal levels with a given depth. They are also
connected through the cousin pointers of the ::hwloc_obj structure.
Object attribute (cache depth and type, group depth) are also taken
in account when gathering objects as horizontal levels.
To be clear: there will be one level for L1i
caches, another level for L1d caches, another one for L2, etc.

If the topology is asymmetric (e.g., if a group is missing above some
processors), a given horizontal level will still exist if there
exist any objects of that type.  However, some branches of the overall
tree may not have an object located in that horizontal level.  Note
that this specific hole within one horizontal level does not imply
anything for other levels.  All objects of the same type are gathered
in horizontal levels even if their parents or children have different
depths and types.

See the diagram in \ref termsanddefs for a graphical representation
of such topologies.

Moreover, it is important to understand that a same parent object may
have children of different types (and therefore, different
depths). <strong>These children are therefore siblings (because they
have the same parent), but they are <em>not</em> cousins (because they
do not belong to the same horizontal level).</strong>


\subsection faq_nosmt What happens to my topology if I disable symmetric multithreading, hyper-threading, etc. in the system?

hwloc creates one PU (processing unit) object per hardware thread.
If your machine supports symmetric multithreading, for instance Hyper-Threading,
each Core object may contain multiple PU objects:
\verbatim
$ lstopo -
...
  Core L#0
    PU L#0 (P#0)
    PU L#1 (P#2)
  Core L#1
    PU L#2 (P#1)
    PU L#3 (P#3)
\endverbatim

x86 machines usually offer the ability to disable hyper-threading in the BIOS.
Or it can be disabled on the Linux kernel command-line at boot time,
or later by writing in sysfs virtual files.

If you do so, the hwloc topology structure does not significantly change,
but some PU objects will not appear anymore.
No level will disappear, you will see the same number of Core objects,
but each of them will contain a single PU now.
The PU level does not disappear either
(remember that hwloc topologies always contain a PU level at the bottom of the topology)
even if there is a single PU object per Core parent.
\verbatim
$ lstopo -
...
  Core L#0
    PU L#0 (P#0)
  Core L#1
    PU L#1 (P#1)
\endverbatim


\subsection faq_smt How may I ignore symmetric multithreading, hyper-threading, etc. in hwloc?

First, see \ref faq_nosmt for more information about multithreading.

If you need to ignore symmetric multithreading in software,
you should likely manipulate hwloc Core objects directly:
\verbatim
/* get the number of cores */
unsigned nbcores = hwloc_get_nbobjs_by_type(topology, HWLOC_OBJ_CORE);
...
/* get the third core below the first package */
hwloc_obj_t package, core;
package = hwloc_get_obj_by_type(topology, HWLOC_OBJ_PACKAGE, 0);
core = hwloc_get_obj_inside_cpuset_by_type(topology, package->cpuset,
                                           HWLOC_OBJ_CORE, 2);
\endverbatim

Whenever you want to bind a process or thread to a core, make sure you
singlify its cpuset first, so that the task is actually bound to a single
thread within this core (to avoid useless migrations).
\verbatim
/* bind on the second core */
hwloc_obj_t core = hwloc_get_obj_by_type(topology, HWLOC_OBJ_CORE, 1);
hwloc_cpuset_t set = hwloc_bitmap_dup(core->cpuset);
hwloc_bitmap_singlify(set);
hwloc_set_cpubind(topology, set, 0);
hwloc_bitmap_free(set);
\endverbatim

With hwloc-calc or hwloc-bind command-line tools, you may specify that
you only want a single-thread within each core by asking for their first
PU object:
\verbatim
$ hwloc-calc core:4-7
0x0000ff00
$ hwloc-calc core:4-7.pu:0
0x00005500
\endverbatim

When binding a process on the command-line, you may either specify
the exact thread that you want to use, or ask hwloc-bind to singlify
the cpuset before binding
\verbatim
$ hwloc-bind core:3.pu:0 -- echo "hello from first thread on core #3"
hello from first thread on core #3
...
$ hwloc-bind core:3 --single -- echo "hello from a single thread on core #3"
hello from a single thread on core #3
\endverbatim



\htmlonly
</div><div class="section" id="faq2">
\endhtmlonly
\section faq2 Advanced



\subsection faq_xml I do not want hwloc to rediscover my enormous machine topology every time I rerun a process

Although the topology discovery is not expensive on common machines,
its overhead may become significant when multiple processes repeat
the discovery on large machines (for instance when starting one process
per core in a parallel application).
The machine topology usually does not vary much, except if some cores
are stopped/restarted or if the administrator restrictions are modified.
Thus rediscovering the whole topology again and again may look useless.

For this purpose, hwloc offers XML import/export and shared memory features.

XML lets you
save the discovered topology to a file (for instance with the lstopo program)
and reload it later by setting the HWLOC_XMLFILE environment variable.
The HWLOC_THISSYSTEM environment variable should also be set to 1 to
assert that loaded file is really the underlying system.

Loading a XML topology is usually much faster than querying multiple
files or calling multiple functions of the operating system.
It is also possible to manipulate such XML files with the C programming
interface, and the import/export may also be directed to memory buffer
(that may for instance be transmitted between applications through a package).
See also \ref xml.

\note The environment variable HWLOC_THISSYSTEM_ALLOWED_RESOURCES
may be used to load a XML topology that contains the entire machine
and restrict it to the part that is actually available to the current
process (e.g. when Linux Cgroup/Cpuset are used to restrict the set
of resources). See \ref envvar.

Shared-memory topologies consist in one process exposing its topology
in a shared-memory buffer so that other processes (running on the same machine)
may use it directly.
This has the advantage of reducing the memory footprint since a single
topology is stored in physical memory for multiple processes.
However, it requires all processes to map this shared-memory buffer
at the same virtual address, which may be difficult in some cases.
This API is described in \ref hwlocality_shmem.


\subsection faq_multitopo How many topologies may I use in my program?

hwloc lets you manipulate multiple topologies at the same time.
However, these topologies consume memory and system resources
(for instance file descriptors) until they are destroyed.
It is therefore discouraged to open the same topology multiple
times.

Sharing a single topology between threads is easy (see \ref threadsafety)
since the vast majority of accesses are read-only.

If multiple topologies of different (but similar) nodes are needed
in your program, have a look at \ref faq_diff.


\subsection faq_diff How to avoid memory waste when manipulating multiple similar topologies?

hwloc does not share information between topologies.
If multiple similar topologies are loaded in memory, for instance
the topologies of different identical nodes of a cluster,
lots of information will be duplicated.

hwloc/diff.h (see also \ref hwlocality_diff) offers the ability to
compute topology differences, apply or unapply them, or export/import
to/from XML.
However, this feature is limited to basic differences such as attribute changes.
It does not support complex modifications such as adding or removing some objects.


\subsection faq_annotate How do I annotate the topology with private notes?

Each hwloc object contains a <tt>userdata</tt> field that may be used by
applications to store private pointers. This field is only valid
during the lifetime of these container object and topology.
It becomes invalid as soon the topology is destroyed,
or as soon as the object disappears, for instance when restricting
the topology.
The userdata field is not exported/imported to/from XML by default since
hwloc does not know what it contains.
This behavior may be changed by specifying application-specific callbacks
with <tt>hwloc_topology_set_userdata_export_callback()</tt>
and <tt>hwloc_topology_set_userdata_import_callback()</tt>.

Each object may also contain some <em>info</em> attributes
(key name and value) that are setup by hwloc during discovery
and that may be extended by the user with
<tt>hwloc_obj_add_info()</tt> (see also \ref attributes).
Contrary to the <tt>userdata</tt> field which is unique, multiple info
attributes may exist for each object, even with the same name.
These attributes are always exported to XML.
However, only character strings may be used as key names and values.

It is also possible to insert Misc objects with a custom name
anywhere as a leaf of the topology (see \ref miscobjs).
And Misc objects may have their own userdata and info attributes
just like any other object.

The hwloc-annotate command-line tool may be used for adding
Misc objects and info attributes.

There is also a topology-specific userdata pointer that can be used
to recognize different topologies by storing a custom pointer.
It may be manipulated with <tt>hwloc_topology_set_userdata()</tt>
and <tt>hwloc_topology_get_userdata()</tt>.


\subsection faq_create_asymmetric How do I create a custom heterogeneous and asymmetric topology?

Synthetic topologies (see \ref synthetic) allow to create custom topologies
but they are always symmetric: same numbers of cores in each package,
same local NUMA nodes, same shared cache, etc.
To create an asymmetric topology, for instance to simulate hybrid CPUs,
one may want to start from a larger symmetric topology and restrict it.
<br/>

Assuming we want two packages, one with 4 dual-threaded cores, and one with 8 single-threaded cores,
first we create a topology with two identical packages, each with 8 dual-threaded cores:
\verbatim
$ lstopo -i "pack:2 core:8 pu:2" topo.xml
\endverbatim
Then create the bitmask representing the PUs that we wish to keep and pass it to lstopo's restrict option:
\verbatim
$ hwloc-calc -i topo.xml pack:0.core:0-3.pu:0-1 pack:1.core:0-7.pu:0
0x555500ff
$ lstopo -i topo.xml --restrict 0x555500ff topo2.xml
$ mv -f topo2.xml topo.xml
\endverbatim
To mark the cores of first package as Big (power hungry)
and those of second package as Little (energy efficient), define CPU kinds:
\verbatim
$ hwloc-annotate topo.xml topo.xml -- none -- cpukind $(hwloc-calc -i topo.xml pack:0) 1 0 CoreType Big
$ hwloc-annotate topo.xml topo.xml -- none -- cpukind $(hwloc-calc -i topo.xml pack:1) 0 0 CoreType Little
\endverbatim
<br/>

A similar method may be used for heterogeneous memory.
First we specify 2 NUMA nodes per package in our synthetic description:
\verbatim
$ lstopo -i "pack:2 [numa(memory=100GB)] [numa(memory=10GB)] core:8 pu:2" topo.xml
\endverbatim
Then remove the second node of first package:
\verbatim
$ hwloc-calc -i topo.xml --nodeset node:all ~pack:0.node:1
0x0000000e
$ lstopo -i topo.xml --restrict nodeset=0xe topo2.xml
$ mv -f topo2.xml topo.xml
\endverbatim
Then make one large node even bigger:
\verbatim
$ hwloc-annotate topo.xml topo.xml -- pack:0.numa:0 -- size 200GB
\endverbatim
Now we have 200GB in first package, and 100GB+10GB in second package.
<br/>

Next we may specify that the small NUMA node (second of second package) is HBM while the large ones are DRAM:
\verbatim
$ hwloc-annotate topo.xml topo.xml -- pack:0.numa:0 pack:1.numa:0 -- subtype DRAM
$ hwloc-annotate topo.xml topo.xml -- pack:1.numa:1 -- subtype HBM
\endverbatim
Finally we may define memory performance attributes to specify that the HBM bandwidth (200GB/s)
from local cores is higher than the DRAM bandwidth (50GB/s):
\verbatim
$ hwloc-annotate topo.xml topo.xml -- pack:0.numa:0 -- memattr Bandwidth pack:0 50000
$ hwloc-annotate topo.xml topo.xml -- pack:1.numa:0 -- memattr Bandwidth pack:1 50000
$ hwloc-annotate topo.xml topo.xml -- pack:1.numa:1 -- memattr Bandwidth pack:1 200000
\endverbatim
<br/>

There is currently no way to create or modify I/O devices attached to such fake topologies.
There is also no way to have some <em>partial levels</em>, e.g. a L3 cache in one package
but not in the other.
<br/>

More changes may obviously be performed by manually modifying the XML export file.
Simple operations such as modifying object attributes (cache size, memory size
info keypairs, etc.), moving I/O subtrees, moving Misc objects, or removing
objects are easy to perform.

However, modifying CPU and Memory objects requires care since cpusets and nodesets
are supposed to remain consistent between parents and children.
Similarly, PCI bus IDs should remain consistent between bridges and children within
an I/O subtree.



\htmlonly
</div><div class="section" id="faq3">
\endhtmlonly
\section faq3 Caveats



\subsection faq_slow_lstopo Why is lstopo slow?

lstopo enables most hwloc objects and discovery flags
by default so that the output topology is as precise as possible
(while hwloc disables many of them by default).
This includes I/O device discovery through PCI libraries as well as external
libraries such as NVML.
To speed up lstopo, you may disable such features with command-line
options such as <tt>\--no-io</tt>.

When NVIDIA GPU probing is enabled (e.g. with CUDA or NVML), one may enable
the <em>Persistent</em> mode (with <tt>nvidia-smi -pm 1</tt>)
to avoid significant GPU wakeup and initialization overhead.

When AMD GPU discovery is enabled with OpenCL and hwloc is used remotely
over ssh, some spurious round-trips on the network may significantly
increase the discovery time.
Forcing the <tt>DISPLAY</tt> environment variable to the remote X server
display (usually <tt>:0</tt>) instead of only setting the <tt>COMPUTE</tt>
variable may avoid this.

Also remember that these hwloc components may be disabled.
At build-time, one may pass configure flags such as <tt>\--disable-opencl</tt>,
<tt>\--disable-cuda</tt>, <tt>\--disable-nvml</tt>, <tt>\--disable-rsmi</tt>,
and <tt>\--disable-levelzero</tt>.
At runtime, one may set the environment variable
<tt>HWLOC_COMPONENTS=-opencl,-cuda,-nvml,-rsmi,-levelzero</tt>
or call hwloc_topology_set_components().

Remember that these backends are disabled by default, except in lstopo.
If hwloc itself is still too slow even after disabling all the I/O devices
as explained above, see also \ref faq_disable_faster for disabling even more
features.


\subsection faq_privileged Does hwloc require privileged access?

hwloc discovers the topology by querying the operating system.
Some minor features may require privileged access to the operation
system.
For instance memory module discovery on Linux is reserved to root,
and the entire PCI discovery on Solaris and BSDs requires access to
some special files that are usually restricted to root
(/dev/pci* or /devices/pci*).

To workaround this limitation, it is recommended to export the
topology as a XML file generated by the administrator (with the
lstopo program) and make it available to all users
(see \ref xml).
It will offer all discovery information to any application without
requiring any privileged access anymore.
Only the necessary hardware characteristics will be exported, no
sensitive information will be disclosed through this XML export.

This XML-based model also has the advantage of speeding up the
discovery because reading a XML topology is usually much faster
than querying the operating system again.

The utility <tt>hwloc-dump-hwdata</tt> is also involved in gathering
privileged information at boot time and making it available to
non-privileged users (note that this may require a specific SELinux
MLS policy module). However, it only applies to Intel Xeon Phi processors
for now (see \ref faq_knl_dump).
See also <tt>HWLOC_DUMPED_HWDATA_DIR</tt> in \ref envvar for details
about the location of dumped files.


\subsection faq_os_error What should I do when hwloc reports "operating system" warnings?

When the operating system reports invalid locality information (because
of either software or hardware bugs), hwloc may fail to insert some objects
in the topology because they cannot fit in the already built tree of resources.
If so, hwloc will report a warning like the following.
The object causing this error is ignored, the discovery continues but the
resulting topology will miss some objects and may be asymmetric
(see also \ref faq_asymmetric).

\verbatim
****************************************************************************
* hwloc received invalid information from the operating system.
*
* L3 (cpuset 0x000003f0) intersects with NUMANode (P#0 cpuset 0x0000003f) without inclusion!
* Error occurred in topology.c line 940
*
* Please report this error message to the hwloc user's mailing list,
* along with the files generated by the hwloc-gather-topology script.
*
* hwloc will now ignore this invalid topology information and continue.
****************************************************************************
\endverbatim

These errors are common on large AMD platforms because of BIOS and/or Linux
kernel bugs causing invalid L3 cache information.
In the above example, the hardware reports
a L3 cache that is shared by 2 cores in the first NUMA node and 4 cores
in the second NUMA node. That's wrong, it should actually be shared by all 6
cores in a single NUMA node.
The resulting topology will miss some L3 caches.

If your application does not care about cache sharing, or if you do not plan to
request cache-aware binding in your process launcher, you may likely ignore
this error (and hide it by setting HWLOC_HIDE_ERRORS=1 in your environment).

Some platforms report similar warnings about conflicting Packages and NUMANodes.

On x86 hosts, passing <tt>HWLOC_COMPONENTS=x86</tt> in the environment may
workaround some of these issues by switching to a different way to discover the topology.

Upgrading the BIOS and/or the operating system may help.
Otherwise, as explained in the message, reporting this issue to the hwloc developers
(by sending the tarball that is generated by the hwloc-gather-topology script
 on this platform) is a good way to make sure that this is a software
(operating system) or hardware bug (BIOS, etc).

See also \ref bugs. Opening an issue on GitHub automatically displays hints
on what information you should provide when reporting such bugs.


\subsection faq_valgrind Why does Valgrind complain about hwloc memory leaks?

If you are debugging your application with Valgrind, you want to
avoid memory leak reports that are caused by hwloc and not by your
program.

hwloc itself is often checked with Valgrind to make sure it does
not leak memory.
However, some global variables in hwloc dependencies are never freed.
For instance libz allocates its global state once at startup and
never frees it so that it may be reused later.
Some libxml2 global state is also never freed because hwloc does not
know whether it can safely ask libxml2 to free it (the application may
also be using libxml2 outside of hwloc).

These unfreed variables cause leak reports in Valgrind.
hwloc installs a Valgrind <em>suppressions</em> file to hide them.
You should pass the following command-line option to Valgrind to use it:
\verbatim
  --suppressions=/path/to/hwloc-valgrind.supp
\endverbatim




\htmlonly
</div><div class="section" id="faq4">
\endhtmlonly
\section faq4 Platform-specific


\subsection faq_rocm_build How do I enable ROCm SMI and select which version to use?

hwloc enables ROCm SMI as soon as it finds its development headers and libraries
on the system.
This detection consists in looking in <tt>/opt/rocm</tt> by default.
If a ROCm version was specified with <tt>\--with-rocm-version=4.4.0</tt>
or in the <tt>ROCM_VERSION</tt> environment variable,
then <tt>/opt/rocm-&lt;version&gt;</tt> is used instead.
Finally, a specific installation path may be specified with <tt>\--with-rocm=/path/to/rocm</tt>.

As usual, developer header and library paths may also be set through
environment variables such as <tt>LIBRARY_PATH</tt> and <tt>C_INCLUDE_PATH</tt>.

To find out whether ROCm SMI was detected and enabled, look in <i>Probe / display I/O devices</i>
at the end of the configure script output.
Passing <tt>\--enable-rsmi</tt> will also cause configure to fail
if RSMI could not be found and enabled in hwloc.



\subsection faq_cuda_build How do I enable CUDA and select which CUDA version to use?

hwloc enables CUDA as soon as it finds CUDA development headers and libraries
on the system.
This detection may be performed thanks to <tt>pkg-config</tt> but it requires
hwloc to know which CUDA version to look for. This may be done by passing
<tt>\--with-cuda-version=11.0</tt> to the configure script. Otherwise hwloc
will also look for the <tt>CUDA_VERSION</tt> environment variable.

If <tt>pkg-config</tt> does not work, passing <tt>\--with-cuda=/path/to/cuda</tt>
to the configure script is another way to define the corresponding library
and header paths.
Finally, these paths may also be set through environment variables such
as <tt>LIBRARY_PATH</tt> and <tt>C_INCLUDE_PATH</tt>.

These paths, either detected by <tt>pkg-config</tt> or given manually, will
also be used to detect NVML and OpenCL libraries and enable their hwloc backends.

To find out whether CUDA was detected and enabled, look in <i>Probe / display I/O devices</i>
at the end of the configure script output.
Passing <tt>\--enable-cuda</tt> will also cause configure to fail
if CUDA could not be found and enabled in hwloc.

Note that <tt>\--with-cuda=/nonexisting</tt> may be used to disable all dependencies
that are installed by CUDA, i.e. the CUDA, NVML and NVIDIA OpenCL backends,
since the given directory does not exist.



\subsection faq_knl_numa How do I find the local MCDRAM NUMA node on Intel Xeon Phi processor?

Intel Xeon Phi processors introduced a new memory architecture by
possibly having two distinct local memories:
some normal memory (DDR) and some high-bandwidth on-package memory (MCDRAM).
Processors can be configured in various clustering modes to have up to 4 <em>Clusters</em>.
Moreover, each <em>Cluster</em> (quarter, half or whole processor) of the processor may have its own local
parts of the DDR and of the MCDRAM.
This memory and clustering configuration may be probed by looking at MemoryMode
and ClusterMode attributes, see \ref attributes_info_platform and doc/examples/get-knl-modes.c
in the source directory.

Starting with version 2.0, hwloc properly exposes this memory
configuration.
DDR and MCDRAM are attached as two memory children of the same parent,
DDR first, and MCDRAM second if any.
Depending on the processor configuration, that parent may be a Package,
a Cache, or a Group object of type <tt>Cluster</tt>.

Hence cores may have one or two local NUMA nodes, listed by the core nodeset.
An application may allocate local memory from a core by using that nodeset.
The operating system will actually allocate from the DDR when
possible, or fallback to the MCDRAM.

To allocate specifically on one of these memories,
one should walk up the parent pointers until finding an object with
some memory children.
Looking at these memory children will give the DDR first,
then the MCDRAM if any.
Their nodeset may then be used for allocating or binding memory buffers.

One may also traverse the list of NUMA nodes until finding some whose
cpuset matches the target core or PUs.
The MCDRAM NUMA nodes may be identified thanks to the <tt>subtype</tt> field
which is set to <tt>MCDRAM</tt>.

Command-line tools such as <tt>hwloc-bind</tt> may bind memory on the MCDRAM by
using the <i>hbm</i> keyword. For instance, to bind on the first MCDRAM NUMA node:

\verbatim
$ hwloc-bind --membind --hbm numa:0 -- myprogram
$ hwloc-bind --membind numa:0 -- myprogram
\endverbatim


\subsection faq_knl_dump Why do I need hwloc-dump-hwdata for memory on Intel Xeon Phi processor?

Intel Xeon Phi processors may use the on-package memory (MCDRAM)
as either memory or a memory-side cache
(reported as a L3 cache by hwloc by default,
see <tt>HWLOC_KNL_MSCACHE_L3</tt> in \ref envvar).
There are also several clustering modes that significantly affect the memory organization
(see \ref faq_knl_numa for more information about these modes).
Details about these are currently only available to privileged users.
Without them, hwloc relies on a heuristic for guessing the modes.

The hwloc-dump-hwdata utility may be used to dump this privileged binary information
into human-readable and world-accessible files that the hwloc library will later load.
The utility should usually run as root once during boot, in order to update dumped
information (stored under /var/run/hwloc by default) in case the MCDRAM or clustering configuration
changed between reboots.

When SELinux MLS policy is enabled, a specific hwloc policy module may be required
so that all users get access to the dumped files (in /var/run/hwloc by default).
One may use hwloc policy files from the SELinux Reference Policy at
https://github.com/TresysTechnology/refpolicy-contrib
(see also the documentation at https://github.com/TresysTechnology/refpolicy/wiki/GettingStarted).

hwloc-dump-hwdata requires <tt>dmi-sysfs</tt> kernel module loaded.

The utility is currently unneeded on platforms without Intel Xeon Phi processors.

See <tt>HWLOC_DUMPED_HWDATA_DIR</tt> in \ref envvar for details
about the location of dumped files.


\subsection faq_bgq How do I build hwloc for BlueGene/Q?

IBM BlueGene/Q machines run a standard Linux on the login/frontend nodes
and a custom CNK (<em>Compute Node Kernel</em>) on the compute nodes.

To discover the topology of a login/frontend node, hwloc should be
configured as usual, without any BlueGene/Q-specific option.

However, one would likely rather discover the topology of the compute nodes
where parallel jobs are actually running.
If so, hwloc must be cross-compiled with the following configuration line:
\verbatim
./configure --host=powerpc64-bgq-linux --disable-shared --enable-static \
  CPPFLAGS='-I/bgsys/drivers/ppcfloor -I/bgsys/drivers/ppcfloor/spi/include/kernel/cnk/'
\endverbatim

CPPFLAGS may have to be updated if your platform headers are installed
in a different directory.


\subsection faq_windows How do I build hwloc for Windows?

<b>hwloc binary releases for Windows are available on the website download pages</b>
(as pre-built ZIPs for both 32bits and 64bits x86 platforms).
However hwloc also offers several ways to build on Windows:

<ul>
<li>
The usual Unix build steps (<tt>configure</tt>, <tt>make</tt> and <tt>make install</tt>)
work on the <b>MSYS2/MinGW</b> environment on Windows
(the official hwloc binary releases are built this way).
Some environment variables and options must be configured,
see <tt>contrib/ci.inria.fr/job-3-mingw.sh</tt> in the hwloc repository
for an example (used for nightly testing).
</li>
<li>
hwloc also supports such Unix-like builds in <b>Cygwin</b>
(environment for porting Unix code to Windows).
</li>
<li>
Windows build is also possible with <b>CMake</b>
(<tt>CMakeLists.txt</tt> available under <tt>contrib/windows-cmake/</tt>).
</li>
<li>
hwloc also comes with an example of <b>Microsoft Visual Studio solution</b>
(under <tt>contrib/windows/</tt>) that may serve as a base for custom builds.
</li>
</ul>


\subsection faq_netbsd_bind How to get useful topology information on NetBSD?

The NetBSD (and FreeBSD) backend uses x86-specific topology discovery
(through the x86 component).
This implementation requires CPU binding so as to query topology
information from each individual processor.
This means that hwloc cannot find any useful topology information
unless user-level process binding is allowed by the NetBSD kernel.
The <tt>security.models.extensions.user_set_cpu_affinity</tt>
sysctl variable must be set to 1 to do so.
Otherwise, only the number of processors will be detected.


\subsection faq_aix_bind Why does binding fail on AIX?

The AIX operating system requires specific user capabilities for
attaching processes to resource sets (CAP_NUMA_ATTACH).
Otherwise functions such as hwloc_set_cpubind() fail (return -1 with errno set to EPERM).

This capability must also be inherited (through the additional CAP_PROPAGATE capability)
if you plan to bind a process before forking another process,
for instance with <tt>hwloc-bind</tt>.

These capabilities may be given by the administrator with:
\verbatim
chuser "capabilities=CAP_PROPAGATE,CAP_NUMA_ATTACH" <username>
\endverbatim


\htmlonly
</div><div class="section" id="faq5">
\endhtmlonly
\section faq5 Compatibility between hwloc versions

\subsection faq_version_api How do I handle API changes?

The hwloc interface is extended with every new major release.
Any application using the hwloc API should be prepared to check at
compile-time whether some features are available in the currently
installed hwloc distribution.

For instance, to check whether the hwloc version is at least 2.0, you should use:
\verbatim
#include <hwloc.h>
#if HWLOC_API_VERSION >= 0x00020000
...
#endif
\endverbatim

To check for the API of release X.Y.Z at build time,
you may compare ::HWLOC_API_VERSION with <tt>(X<<16)+(Y<<8)+Z</tt>.

For supporting older releases that do not have <tt>HWLOC_OBJ_NUMANODE</tt>
and <tt>HWLOC_OBJ_PACKAGE</tt> yet, you may use:

\verbatim
#include <hwloc.h>
#if HWLOC_API_VERSION < 0x00010b00
#define HWLOC_OBJ_NUMANODE HWLOC_OBJ_NODE
#define HWLOC_OBJ_PACKAGE HWLOC_OBJ_SOCKET
#endif
\endverbatim

Once a program is built against a hwloc library, it may also dynamically
link with compatible libraries from other hwloc releases.
The version of that runtime library may be queried with hwloc_get_api_version().
For instance, the following code enables the topology flag ::HWLOC_TOPOLOGY_FLAG_NO_DISTANCES
when compiling on hwloc 2.8 or later, but it disables it at runtime if running
on an older hwloc (otherwise hwloc_topology_set_flags() would fail).

\verbatim
unsigned long topology_flags = ...; /* wanted flags that were supported before 2.8 */
#if HWLOC_API_VERSION >= 0x20800
if (hwloc_get_api_version() >= 0x20800)
  topology_flags |= HWLOC_TOPOLOGY_FLAG_NO_DISTANCES; /* wanted flags only supported in 2.8+ */
#endif
hwloc_topology_set_flags(topology, topology_flags);
\endverbatim

See also \ref faq_version_abi for using hwloc_get_api_version() for testing ABI compatibility.


\subsection faq_version What is the difference between API and library version numbers?

::HWLOC_API_VERSION is the version of the API.
It changes when functions are added, modified, etc.
However it does not necessarily change from one release to another.
For instance, two releases of the same series (e.g. 2.0.3 and 2.0.4)
usually have the same ::HWLOC_API_VERSION (<tt>0x00020000</tt>).
However their HWLOC_VERSION strings are different
(<tt>\"2.0.3\"</tt> and <tt>\"2.0.4\"</tt> respectively).



\subsection faq_version_abi How do I handle ABI breaks?

The hwloc interface was deeply modified in release 2.0
to fix several issues of the 1.x interface
(see \ref upgrade_to_api_2x and the NEWS file in the source directory for details).
The ABI was broken, which means
<b>applications must be recompiled against the new 2.0 interface</b>.

To check that you are not mixing old/recent headers with a recent/old runtime library,
check the major revision number in the API version:
\verbatim
#include <hwloc.h>
  unsigned version = hwloc_get_api_version();
  if ((version >> 16) != (HWLOC_API_VERSION >> 16)) {
    fprintf(stderr,
           "%s compiled for hwloc API 0x%x but running on library API 0x%x.\n"
           "You may need to point LD_LIBRARY_PATH to the right hwloc library.\n"
           "Aborting since the new ABI is not backward compatible.\n",
           callname, HWLOC_API_VERSION, version);
    exit(EXIT_FAILURE);
  }
\endverbatim
To specifically detect v2.0 issues:
\verbatim
#include <hwloc.h>
#if HWLOC_API_VERSION >= 0x00020000
  /* headers are recent */
  if (hwloc_get_api_version() < 0x20000)
    ... error out, the hwloc runtime library is older than 2.0 ...
#else
  /* headers are pre-2.0 */
  if (hwloc_get_api_version() >= 0x20000)
    ... error out, the hwloc runtime library is more recent than 2.0 ...
#endif
\endverbatim

In theory, library sonames prevent linking with incompatible libraries.
However custom hwloc installations or improperly configured build environments
may still lead to such issues.
Hence running one of the above (cheap) checks before initializing hwloc topology
may be useful.



\subsection faq_version_xml Are XML topology files compatible between hwloc releases?

XML topology files are forward-compatible:
a XML file may be loaded by a hwloc library that is more recent
than the hwloc release that exported that file.

However, hwloc XMLs are not always backward-compatible:
Topologies exported by hwloc 2.x cannot be imported by 1.x by default
(see \ref upgrade_to_api_2x_xml for working around such issues).
There are also some corner cases where backward compatibility
is not guaranteed because of changes between major releases
(for instance 1.11 XMLs could not be imported in 1.10).

XMLs are exchanged at runtime between some components of the HPC software stack
(for instance the resource managers and MPI processes).
Building all these components on the same (cluster-wide)
hwloc installation is a good way to avoid such incompatibilities.



\subsection faq_version_synthetic Are synthetic strings compatible between hwloc releases?

Synthetic strings (see \ref synthetic) are forward-compatible:
a synthetic string generated by a release may be imported by future hwloc libraries.

However they are often not backward-compatible because new details may have been
added to synthetic descriptions in recent releases.
Some flags may be given to hwloc_topology_export_synthetic() to avoid such details
and stay backward compatible.



\subsection faq_version_shmem Is it possible to share a shared-memory topology between different hwloc releases?

Shared-memory topologies (see \ref hwlocality_shmem) have strong
requirements on compatibility between hwloc libraries.
Adopting a shared-memory topology fails
if it was exported by a non-compatible hwloc release.
Releases with same major revision are usually compatible
(e.g. hwloc 2.0.4 may adopt a topology exported by 2.0.3)
but different major revisions may be incompatible
(e.g. hwloc 2.1.0 cannot adopt from 2.0.x).

Topologies are shared at runtime between some components of the HPC software stack
(for instance the resource managers and MPI processes).
Building all these components on the same (system-wide) hwloc installation
is a good way to avoid such incompatibilities.



\page upgrade_to_api_2x Upgrading to the hwloc 2.0 API

\htmlonly
<div class="section">
\endhtmlonly

See \ref faq5 for detecting the hwloc version that you are compiling
and/or running against.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_memory">
\endhtmlonly
\section upgrade_to_api_2x_memory New Organization of NUMA nodes and Memory

\subsection upgrade_to_api_2x_memory_children Memory children

In hwloc v1.x, NUMA nodes were inside the tree, for instance Packages
contained 2 NUMA nodes which contained a L3 and several cache.

Starting with hwloc v2.0, NUMA nodes are not in the main tree anymore.
They are attached under objects as <i>Memory Children</i> on the side
of normal children.
This memory children list starts at <code>obj->memory_first_child</code>
and its size is <code>obj->memory_arity</code>.
Hence there can now exist two local NUMA nodes,
for instance on Intel Xeon Phi processors.

The normal list of children (starting at <code>obj->first_child</code>,
ending at <code>obj->last_child</code>, of size <code>obj->arity</code>,
and available as the array <code>obj->children</code>)
now only contains CPU-side objects:
PUs, Cores, Packages, Caches, Groups, Machine and System.
hwloc_get_next_child() may still be used to iterate over all children of all lists.

Hence the CPU-side hierarchy is built using normal children,
while memory is attached to that hierarchy depending on its affinity.

\subsection upgrade_to_api_2x_memory_examples Examples

<ul>
<li>a UMA machine with 2 packages and a single NUMA node is now modeled
 as a "Machine" object with two "Package" children
 and one "NUMANode" memory children (displayed first in lstopo below):
\verbatim
Machine (1024MB total)
  NUMANode L#0 (P#0 1024MB)
  Package L#0
    Core L#0 + PU L#0 (P#0)
    Core L#1 + PU L#1 (P#1)
  Package L#1
    Core L#2 + PU L#2 (P#2)
    Core L#3 + PU L#3 (P#3)
\endverbatim
</li>

<li>a machine with 2 packages with one NUMA node and 2 cores in each is now:
\verbatim
Machine (2048MB total)
  Package L#0
    NUMANode L#0 (P#0 1024MB)
    Core L#0 + PU L#0 (P#0)
    Core L#1 + PU L#1 (P#1)
  Package L#1
    NUMANode L#1 (P#1 1024MB)
    Core L#2 + PU L#2 (P#2)
    Core L#3 + PU L#3 (P#3)
\endverbatim
</li>

<li>if there are two NUMA nodes per package, a Group object may be added to keep
cores together with their local NUMA node:
\verbatim
Machine (4096MB total)
  Package L#0
    Group0 L#0
      NUMANode L#0 (P#0 1024MB)
      Core L#0 + PU L#0 (P#0)
      Core L#1 + PU L#1 (P#1)
    Group0 L#1
      NUMANode L#1 (P#1 1024MB)
      Core L#2 + PU L#2 (P#2)
      Core L#3 + PU L#3 (P#3)
  Package L#1
    [...]
\endverbatim
</li>

<li>if the platform has L3 caches whose localities are identical to NUMA nodes, Groups aren't needed:
\verbatim
Machine (4096MB total)
  Package L#0
    L3 L#0 (16MB)
      NUMANode L#0 (P#0 1024MB)
      Core L#0 + PU L#0 (P#0)
      Core L#1 + PU L#1 (P#1)
    L3 L#1 (16MB)
      NUMANode L#1 (P#1 1024MB)
      Core L#2 + PU L#2 (P#2)
      Core L#3 + PU L#3 (P#3)
  Package L#1
    [...]
\endverbatim
</li>
</ul>


\subsection upgrade_to_api_2x_numa_level NUMA level and depth

NUMA nodes are not in "main" tree of normal objects anymore.
Hence, they don't have a meaningful depth anymore (like I/O and Misc objects).
They have a virtual (negative) depth (::HWLOC_TYPE_DEPTH_NUMANODE)
so that functions manipulating depths and level still work,
and so that we can still iterate over the level of NUMA nodes just like for any other level.

For instance we can still use lines such as
\verbatim
int depth = hwloc_get_type_depth(topology, HWLOC_OBJ_NUMANODE);
hwloc_obj_t obj = hwloc_get_obj_by_type(topology, HWLOC_OBJ_NUMANODE, 4);
hwloc_obj_t node = hwloc_get_next_obj_by_depth(topology, HWLOC_TYPE_DEPTH_NUMANODE, prev);
\endverbatim

The NUMA depth should not be compared with others.
An unmodified code that still compares NUMA and Package depths
(to find out whether Packages contain NUMA or the contrary)
would now always assume Packages contain NUMA (because the NUMA depth is negative).

However, the depth of the Normal parents of NUMA nodes may be used instead.
In the last example above, NUMA nodes are attached to L3 caches,
hence one may compare the depth of Packages and L3 to find out
that NUMA nodes are contained in Packages.
This depth of parents may be retrieved with hwloc_get_memory_parents_depth().
However, this function may return ::HWLOC_TYPE_DEPTH_MULTIPLE
on future platforms if NUMA nodes are attached to different levels.


\subsection upgrade_to_api_2x_memory_find Finding Local NUMA nodes and looking at Children and Parents

Applications that walked up/down to find NUMANode parent/children must
now be updated.
Instead of looking directly for a NUMA node, one should now look for
an object that has some memory children.
NUMA node(s) will be attached there.
For instance, when looking for a NUMA node above a given core <tt>core</tt>:
\verbatim
hwloc_obj_t parent = core->parent;
while (parent && !parent->memory_arity)
  parent = parent->parent; /* no memory child, walk up */
if (parent)
  /* use parent->memory_first_child (and its siblings if there are multiple local NUMA nodes) */
\endverbatim

The list of local NUMA nodes (usually a single one) is also described
by the <tt>nodeset</tt> attribute of each object (which contains the
physical indexes of these nodes).
Iterating over the NUMA level is also an easy way to find local NUMA nodes:
\verbatim
hwloc_obj_t tmp = NULL;
while ((tmp = hwloc_get_next_obj_by_type(topology, HWLOC_OBJ_NUMANODE, tmp)) != NULL) {
  if (hwloc_bitmap_isset(obj->nodeset, tmp->os_index))
    /* tmp is a NUMA node local to obj, use it */
}
\endverbatim

Similarly finding objects that are close to a given NUMA nodes
should be updated too.
Instead of looking at the NUMA node parents/children, one should
now find a Normal parent above that NUMA node, and then look
at its parents/children as usual:
\verbatim
hwloc_obj_t tmp = obj->parent;
while (hwloc_obj_type_is_memory(tmp))
  tmp = tmp->parent;
/* now use tmp instead of obj */
\endverbatim

To avoid such hwloc v2.x-specific and NUMA-specific cases in the code,
a <b>generic lookup for any kind of object, including NUMA nodes</b>,
might also be implemented by iterating over a level.
For instance finding an object of type <tt>type</tt> which either
contains or is included in object <tt>obj</tt> can be
performed by traversing the level of that type and comparing CPU sets:
\verbatim
hwloc_obj_t tmp = NULL;
while ((tmp = hwloc_get_next_obj_by_type(topology, type, tmp)) != NULL) {
  if (hwloc_bitmap_intersects(tmp->cpuset, obj->cpuset))
    /* tmp matches, use it */
}
\endverbatim
<b>
This generic lookup works whenever <tt>type</tt> or <tt>obj</tt>
are Normal or Memory objects since both have CPU sets.
Moreover, it is compatible with the hwloc v1.x API.
</b>




\htmlonly
</div><div class="section" id="upgrade_to_api_2x_children">
\endhtmlonly
\section upgrade_to_api_2x_children 4 Kinds of Objects and Children

\subsection upgrade_to_api_2x_io_misc_children I/O and Misc children

I/O children are not in the main object children list anymore either.
They are in the list starting at <code>obj->io_first_child</code>
and its size is <code>obj->io_arity</code>.

Misc children are not in the main object children list anymore.
They are in the list starting at <code>obj->misc_first_child</code>
and its size is <code>obj->misc_arity</code>.

See hwloc_obj for details about children lists.

hwloc_get_next_child() may still be used to iterate over all children of all lists.


\subsection upgrade_to_api_2x_kinds_subsec Kinds of objects

Given the above, objects may now be of 4 kinds:
<ul>
<li>Normal (everything not listed below, including Machine, Package, Core, PU, CPU Caches, etc);</li>
<li>Memory (currently NUMA nodes or Memory-side Caches), attached to parents as Memory children;</li>
<li>I/O (Bridges, PCI and OS devices), attached to parents as I/O children;</li>
<li>Misc objects, attached to parents as Misc children.</li>
</ul>
See hwloc_obj for details about children lists.

For a given object type, the kind may be found with hwloc_obj_type_is_normal(),
hwloc_obj_type_is_memory(), hwloc_obj_type_is_normal(),
or comparing with ::HWLOC_OBJ_MISC.

Normal and Memory objects have (non-NULL) CPU sets and nodesets,
while I/O and Misc objects don't have any sets (they are NULL).


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_cache">
\endhtmlonly
\section upgrade_to_api_2x_cache HWLOC_OBJ_CACHE replaced

Instead of a single HWLOC_OBJ_CACHE, there are now 8 types
::HWLOC_OBJ_L1CACHE, ..., ::HWLOC_OBJ_L5CACHE,
::HWLOC_OBJ_L1ICACHE, ..., ::HWLOC_OBJ_L3ICACHE.

Cache object attributes are unchanged.

hwloc_get_cache_type_depth() is not needed to disambiguate cache types anymore
since new types can be passed to hwloc_get_type_depth()
without ever getting ::HWLOC_TYPE_DEPTH_MULTIPLE anymore.

hwloc_obj_type_is_cache(), hwloc_obj_type_is_dcache() and hwloc_obj_type_is_icache()
may be used to check whether a given type is a cache, data/unified cache or instruction cache.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_allowed">
\endhtmlonly
\section upgrade_to_api_2x_allowed allowed_cpuset and allowed_nodeset only in the main topology

Objects do not have <code>allowed_cpuset</code> and <code>allowed_nodeset</code> anymore.
They are only available for the entire topology using
hwloc_topology_get_allowed_cpuset() and hwloc_topology_get_allowed_nodeset().

As usual, those are only needed when the INCLUDE_DISALLOWED topology flag is given,
which means disallowed objects are kept in the topology.
If so, one may find out whether some PUs inside an object is allowed by checking
\verbatim
hwloc_bitmap_intersects(obj->cpuset, hwloc_topology_get_allowed_cpuset(topology))
\endverbatim
Replace cpusets with nodesets for NUMA nodes.
To find out which ones, replace intersects() with and() to get the actual intersection.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_depth">
\endhtmlonly
\section upgrade_to_api_2x_depth Object depths are now signed int

<code>obj->depth</code> as well as depths given to functions
such as hwloc_get_obj_by_depth() or returned by hwloc_topology_get_depth() are now
<b>signed int</b>.

Other depth such as cache-specific depth attribute are still unsigned.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_memory_attrs">
\endhtmlonly
\section upgrade_to_api_2x_memory_attrs Memory attributes become NUMANode-specific

Memory attributes such as <code>obj->memory.local_memory</code>
are now only available in NUMANode-specific attributes
in <code>obj->attr->numanode.local_memory</code>.

<code>obj->memory.total_memory</code> is available
in all objects as <code>obj->total_memory</code>.

See hwloc_obj_attr_u::hwloc_numanode_attr_s and hwloc_obj for details.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_config">
\endhtmlonly
\section upgrade_to_api_2x_config Topology configuration changes

The old ignoring API as well as several configuration flags
are replaced with the new filtering API,
see hwloc_topology_set_type_filter() and its variants,
and ::hwloc_type_filter_e for details.

<ul>

<li>
hwloc_topology_ignore_type(), hwloc_topology_ignore_type_keep_structure()
and hwloc_topology_ignore_all_keep_structure() are respectively superseded by
\verbatim
hwloc_topology_set_type_filter(topology, type, HWLOC_TYPE_FILTER_KEEP_NONE);
hwloc_topology_set_type_filter(topology, type, HWLOC_TYPE_FILTER_KEEP_STRUCTURE);
hwloc_topology_set_all_types_filter(topology, HWLOC_TYPE_FILTER_KEEP_STRUCTURE);
\endverbatim

Also, the meaning of KEEP_STRUCTURE has changed (only entire levels may be ignored, instead of single objects), the old behavior is not available anymore.
</li>

<li>
HWLOC_TOPOLOGY_FLAG_ICACHES is superseded by
\verbatim
hwloc_topology_set_icache_types_filter(topology, HWLOC_TYPE_FILTER_KEEP_ALL);
\endverbatim
</li>

<li>
HWLOC_TOPOLOGY_FLAG_WHOLE_IO, HWLOC_TOPOLOGY_FLAG_IO_DEVICES and HWLOC_TOPOLOGY_FLAG_IO_BRIDGES replaced.

To keep all I/O devices (PCI, Bridges, and OS devices), use:
\verbatim
hwloc_topology_set_io_types_filter(topology, HWLOC_TYPE_FILTER_KEEP_ALL);
\endverbatim

To only keep important devices (Bridges with children, common PCI devices and OS devices):
\verbatim
hwloc_topology_set_io_types_filter(topology, HWLOC_TYPE_FILTER_KEEP_IMPORTANT);
\endverbatim
</li>

</ul>


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_xml">
\endhtmlonly
\section upgrade_to_api_2x_xml XML changes

2.0 XML files are not compatible with 1.x

2.0 can load 1.x files, but only NUMA distances are imported. Other distance matrices are ignored
 (they were never used by default anyway).

2.0 can export 1.x-compatible files, but only distances attached to the root object are exported
(i.e. distances that cover the entire machine).
Other distance matrices are dropped (they were never used by default anyway).

<b>Users are advised to negociate hwloc versions between exporter and importer:</b>
If the importer isn't 2.x, the exporter should export to 1.x.
Otherwise, things should work by default.

Hence hwloc_topology_export_xml() and hwloc_topology_export_xmlbuffer() have a new flags argument.
to force a hwloc-1.x-compatible XML export.
<ul>
<li>
 If both always support 2.0, don't pass any flag.
</li>
<li>
 When the importer uses hwloc 1.x, export with ::HWLOC_TOPOLOGY_EXPORT_XML_FLAG_V1.
 Otherwise the importer will fail to import.
</li>
<li>
 When the exporter uses hwloc 1.x, it cannot pass any flag,
 and a 2.0 importer can import without problem.
</li>
</ul>

\verbatim
#if HWLOC_API_VERSION >= 0x20000
   if (need 1.x compatible XML export)
      hwloc_topology_export_xml(...., HWLOC_TOPOLOGY_EXPORT_XML_FLAG_V1);
   else /* need 2.x compatible XML export */
      hwloc_topology_export_xml(...., 0);
#else
   hwloc_topology_export_xml(....);
#endif
\endverbatim

Additionally, hwloc_topology_diff_load_xml(), hwloc_topology_diff_load_xmlbuffer(),
hwloc_topology_diff_export_xml(), hwloc_topology_diff_export_xmlbuffer()
and hwloc_topology_diff_destroy() lost the topology argument:
The first argument (topology) isn't needed anymore.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_distances">
\endhtmlonly
\section upgrade_to_api_2x_distances Distances API totally rewritten

The new distances API is in hwloc/distances.h.

Distances are not accessible directly from objects anymore.
One should first call hwloc_distances_get() (or a variant)
to retrieve distances (possibly with one call to get the
number of available distances structures, and another call
to actually get them).
Then it may consult these structures, and finally release them.

The set of object involved in a distances structure is specified
by an array of objects, it may not always cover the entire machine or so.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_return">
\endhtmlonly
\section upgrade_to_api_2x_return Return values of functions

Bitmap functions (and a couple other functions) can return errors (in theory).

Most bitmap functions may have to reallocate the internal bitmap storage.
In v1.x, they would silently crash if realloc failed.
In v2.0, they now return an int that can be negative on error.
However, the preallocated storage is 512 bits,
hence realloc will not even be used unless you run
hwloc on machines with larger PU or NUMAnode indexes.

hwloc_obj_add_info(), hwloc_cpuset_from_nodeset() and hwloc_cpuset_from_nodeset()
also return an int, which would be -1 in case of allocation errors.


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_misc">
\endhtmlonly
\section upgrade_to_api_2x_misc Misc API changes

<ul>

<li>
hwloc_type_sscanf() extends hwloc_obj_type_sscanf()
by passing a union hwloc_obj_attr_u which may receive
Cache, Group, Bridge or OS device attributes.
</li>

<li>
hwloc_type_sscanf_as_depth() is also added to
directly return the corresponding level depth within a topology.
</li>

<li>
hwloc_topology_insert_misc_object_by_cpuset() is replaced
with hwloc_topology_alloc_group_object() and hwloc_topology_insert_group_object().
</li>

<li>
hwloc_topology_insert_misc_object_by_parent() is replaced
with hwloc_topology_insert_misc_object().
</li>

</ul>


\htmlonly
</div><div class="section" id="upgrade_to_api_2x_removals">
\endhtmlonly
\section upgrade_to_api_2x_removals API removals and deprecations

<ul>

<li>
HWLOC_OBJ_SYSTEM removed:
The root object is always ::HWLOC_OBJ_MACHINE
</li>

<li>
*_membind_nodeset() memory binding interfaces deprecated:
One should use the variant without _nodeset suffix and pass the ::HWLOC_MEMBIND_BYNODESET flag.
</li>

<li>
HWLOC_MEMBIND_REPLICATE removed:
no supported operating system supports it anymore.
</li>

<li>
hwloc_obj_snprintf() removed because it was long-deprecated
by hwloc_obj_type_snprintf() and hwloc_obj_attr_snprintf().
</li>

<li>
hwloc_obj_type_sscanf() deprecated, hwloc_obj_type_of_string() removed.
</li>

<li>
hwloc_cpuset_from/to_nodeset_strict() deprecated:
Now useless since all topologies are NUMA. Use the variant without the _strict suffix
</li>

<li>
hwloc_distribute() and hwloc_distributev() removed,
deprecated by hwloc_distrib().
</li>

<li>
The Custom interface (hwloc_topology_set_custom(), etc.)
was removed, as well as the corresponding command-line tools (hwloc-assembler, etc.).
Topologies always start with object with valid cpusets and nodesets.
</li>

<li>
<code>obj->online_cpuset</code> removed:
Offline PUs are simply listed in the <code>complete_cpuset</code> as previously.
</li>

<li>
<code>obj->os_level</code> removed.
</li>

</ul>



*/
