@cindex Profiling, statistical

The @code{sb-sprof} module, loadable by
@lisp
(require :sb-sprof)
@end lisp
provides an alternate profiler which works by taking samples of the
program execution at regular intervals, instead of instrumenting
functions like @code{sb-profile:profile} does. You might find
@code{sb-sprof} more useful than the deterministic profiler when profiling
functions in the @code{common-lisp}-package, SBCL internals, or code
where the instrumenting overhead is excessive.

Additionally @code{sb-sprof} includes a limited deterministic profiler
which can be used for reporting the amounts of calls to some functions
during

@subsection Example Usage

@lisp
(in-package :cl-user)

(require :sb-sprof)

(declaim (optimize speed))

(defun cpu-test-inner (a i)
  (logxor a
          (* i 5)
          (+ a i)))

(defun cpu-test (n)
  (let ((a 0))
    (dotimes (i (expt 2 n) a)
      (setf a (cpu-test-inner a i)))))

;;;; CPU profiling

;;; Take up to 1000 samples of running (CPU-TEST 26), and give a flat
;;; table report at the end. Profiling will end one the body has been
;;; evaluated once, whether or not 1000 samples have been taken.
(sb-sprof:with-profiling (:max-samples 1000
                          :report :flat
                          :loop nil)
  (cpu-test 26))

;;; Record call counts for functions defined on symbols in the CL-USER
;;; package.
(sb-sprof:profile-call-counts "CL-USER")

;;; Take 1000 samples of running (CPU-TEST 24), and give a flat
;;; table report at the end. The body will be re-evaluated in a loop
;;; until 1000 samples have been taken. A sample count will be printed
;;; after each iteration.
(sb-sprof:with-profiling (:max-samples 1000
                          :report :flat
                          :loop t
                          :show-progress t)
  (cpu-test 24))

;;;; Allocation profiling

(defun foo (&rest args)
  (mapcar (lambda (x) (float x 1d0)) args))

(defun bar (n)
  (declare (fixnum n))
  (apply #'foo (loop repeat n collect n)))

(sb-sprof:with-profiling (:max-samples 10000
                          :mode :alloc
                          :report :flat)
  (bar 1000))
@end lisp

@subsection Output

The flat report format will show a table of all functions that the
profiler encountered on the call stack during sampling, ordered by the
number of samples taken while executing that function.

@lisp
           Self        Total        Cumul
  Nr  Count     %  Count     %  Count     %    Calls  Function
------------------------------------------------------------------------
   1     69  24.4     97  34.3     69  24.4 67108864  CPU-TEST-INNER
   2     64  22.6     64  22.6    133  47.0        -  SB-VM::GENERIC-+
   3     39  13.8    256  90.5    172  60.8        1  CPU-TEST
   4     31  11.0     31  11.0    203  71.7        -  SB-KERNEL:TWO-ARG-XOR
@end lisp

For each function, the table will show three absolute and relative
sample counts. The Self column shows samples taken while directly
executing that function. The Total column shows samples taken while
executing that function or functions called from it (sampled to a
platform-specific depth). The Cumul column shows the sum of all
Self columns up to and including that line in the table.

Additionally the Calls column will record the amount of calls that were
made to the function during the profiling run. This value will only
be reported for functions that have been explicitly marked for call counting
with @code{profile-call-counts}.

The profiler also hooks into the disassembler such that instructions which
have been sampled are annotated with their relative frequency of
sampling.  This information is not stored across different sampling
runs.

@lisp
;      6CF:       702E             JO L4              ; 6/242 samples
;      6D1:       D1E3             SHL EBX, 1
;      6D3:       702A             JO L4
;      6D5: L2:   F6C303           TEST BL, 3         ; 2/242 samples
;      6D8:       756D             JNE L8
;      6DA:       8BC3             MOV EAX, EBX       ; 5/242 samples
;      6DC: L3:   83F900           CMP ECX, 0         ; 4/242 samples
@end lisp

@subsection Platform support

This module is known not to work consistently on the Alpha platform,
for technical reasons related to the implementation of a machine
language idiom for marking sections of code to be treated as atomic by
the garbage collector;  However, it should work on other platforms,
and the deficiency on the Alpha will eventually be rectified.

Allocation profiling is only supported on SBCL builds that use
the generational garbage collector. Tracking of call stacks at a
depth of more than two levels is only supported on x86 and x86-64.

@subsection Macros

@include macro-sb-sprof-with-profiling.texinfo
@include macro-sb-sprof-with-sampling.texinfo

@subsection Functions

@include fun-sb-sprof-map-traces.texinfo

@include fun-sb-sprof-map-trace-samples.texinfo

@include fun-sb-sprof-map-all-samples.texinfo

@include fun-sb-sprof-sample-pc.texinfo

@include fun-sb-sprof-report.texinfo

@include fun-sb-sprof-reset.texinfo

@include fun-sb-sprof-start-profiling.texinfo

@include fun-sb-sprof-stop-profiling.texinfo

@include fun-sb-sprof-profile-call-counts.texinfo

@include fun-sb-sprof-unprofile-call-counts.texinfo

@subsection Variables

@include var-sb-sprof-star-max-samples-star.texinfo

@include var-sb-sprof-star-sample-interval-star.texinfo

@subsection Credits

@code{sb-sprof} is an SBCL port, with enhancements, of Gerd
Moellmann's statistical profiler for CMUCL.
