@node Profiling of program phases
@section Profiling of program phases

The module @samp{timevar} provides a simple self-profiling facility,
based on timers.

@smallexample
Execution times (seconds)
read                  :   0.09 (19%) usr   0.08 (80%) sys   0.09 (18%) wall
read: scan            :   0.04 ( 9%) usr   0.08 (80%) sys   0.12 (26%) wall
read: parse           :   0.05 (10%) usr   0.00 ( 0%) sys   0.05 (10%) wall
work                  :   0.33 (70%) usr   0.00 ( 0%) sys   0.35 (71%) wall
work: phase 1         :   0.30 (64%) usr   0.00 ( 0%) sys   0.30 (64%) wall
work: phase 2         :   0.13 (28%) usr   0.00 ( 0%) sys   0.14 (29%) wall
output                :   0.04 ( 9%) usr   0.02 (20%) sys   0.04 ( 8%) wall
total time            :   0.47             0.10             0.49
@end smallexample

To set up @code{timevar}, copy the stub file
@file{gnulib/lib/timevar.def} next to where @file{timevar.h} and
@file{timevar.c} were imported in your project, and define your timers
there.  For instance:

@smallexample
/* The total execution time.  Mandatory.  */
DEFTIMEVAR (tv_total,      "total time")

/* Examples.  */
DEFTIMEVAR (tv_read,       "read")
DEFTIMEVAR (tv_work,       "work")
DEFTIMEVAR (tv_work_1,     "work: phase 1")
DEFTIMEVAR (tv_work_2,     "work: phase 2")
DEFTIMEVAR (tv_output,     "output")
@end smallexample

Do not remove @code{tv_total}, it is mandatory.  You may change its
associated string.

@sp 1

Use @code{timevar_push}/@code{timevar_pop} to start/stop timers, as in
the following example.

@smallexample
#include <config.h>
#include "timevar.h"

#include <stdio.h>
#include "read.h"
#include "work.h"
#include "output.h"

int
main (void)
@{
  timevar_enabled = true;
  timevar_init ();
  timevar_start (tv_total);

  timevar_push (tv_read);
  reader ();
  timevar_pop (tv_read);

  timevar_push (tv_work);
  work ();
  timevar_pop (tv_work);

  timevar_push (tv_output);
  output ();
  timevar_pop (tv_output);

  timevar_stop (tv_total);
  timevar_print (stderr);
@}
@end smallexample

@noindent
with, for instance, in @file{work.c}

@smallexample
#include <config.h>
#include "work.h"

void
work (void)
@{
  timevar_push (tv_work_phase1);
  work1 ();
  timevar_pop (tv_work_phase1);

  timevar_push (tv_work_phase2);
  work2 ();
  timevar_pop (tv_work_phase2);
@}
@end smallexample