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Devel::DProf

Perl 5 version 8.8 documentation
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Devel::DProf

NAME

Devel::DProf - a Perl code profiler

SYNOPSIS

  1. perl -d:DProf test.pl

DESCRIPTION

The Devel::DProf package is a Perl code profiler. This will collect information on the execution time of a Perl script and of the subs in that script. This information can be used to determine which subroutines are using the most time and which subroutines are being called most often. This information can also be used to create an execution graph of the script, showing subroutine relationships.

To profile a Perl script run the perl interpreter with the -d debugging switch. The profiler uses the debugging hooks. So to profile script test.pl the following command should be used:

  1. perl -d:DProf test.pl

When the script terminates (or when the output buffer is filled) the profiler will dump the profile information to a file called tmon.out. A tool like dprofpp can be used to interpret the information which is in that profile. The following command will print the top 15 subroutines which used the most time:

  1. dprofpp

To print an execution graph of the subroutines in the script use the following command:

  1. dprofpp -T

Consult dprofpp for other options.

PROFILE FORMAT

The old profile is a text file which looks like this:

  1. #fOrTyTwO
  2. $hz=100;
  3. $XS_VERSION='DProf 19970606';
  4. # All values are given in HZ
  5. $rrun_utime=2; $rrun_stime=0; $rrun_rtime=7
  6. PART2
  7. + 26 28 566822884 DynaLoader::import
  8. - 26 28 566822884 DynaLoader::import
  9. + 27 28 566822885 main::bar
  10. - 27 28 566822886 main::bar
  11. + 27 28 566822886 main::baz
  12. + 27 28 566822887 main::bar
  13. - 27 28 566822888 main::bar
  14. [....]

The first line is the magic number. The second line is the hertz value, or clock ticks, of the machine where the profile was collected. The third line is the name and version identifier of the tool which created the profile. The fourth line is a comment. The fifth line contains three variables holding the user time, system time, and realtime of the process while it was being profiled. The sixth line indicates the beginning of the sub entry/exit profile section.

The columns in PART2 are:

  1. sub entry(+)/exit(-) mark
  2. app's user time at sub entry/exit mark, in ticks
  3. app's system time at sub entry/exit mark, in ticks
  4. app's realtime at sub entry/exit mark, in ticks
  5. fully-qualified sub name, when possible

With newer perls another format is used, which may look like this:

  1. #fOrTyTwO
  2. $hz=10000;
  3. $XS_VERSION='DProf 19971213';
  4. # All values are given in HZ
  5. $over_utime=5917; $over_stime=0; $over_rtime=5917;
  6. $over_tests=10000;
  7. $rrun_utime=1284; $rrun_stime=0; $rrun_rtime=1284;
  8. $total_marks=6;
  9. PART2
  10. @ 406 0 406
  11. & 2 main bar
  12. + 2
  13. @ 456 0 456
  14. - 2
  15. @ 1 0 1
  16. & 3 main baz
  17. + 3
  18. @ 141 0 141
  19. + 2
  20. @ 141 0 141
  21. - 2
  22. @ 1 0 1
  23. & 4 main foo
  24. + 4
  25. @ 142 0 142
  26. + & Devel::DProf::write
  27. @ 5 0 5
  28. - & Devel::DProf::write

(with high value of $ENV{PERL_DPROF_TICKS}).

New $over_* values show the measured overhead of making $over_tests calls to the profiler These values are used by the profiler to subtract the overhead from the runtimes.

The lines starting with @ mark time passed from the previous @ line. The lines starting with & introduce new subroutine id and show the package and the subroutine name of this id. Lines starting with + , - and * mark entering and exit of subroutines by ids, and goto &subr .

The old-style + - and - -lines are used to mark the overhead related to writing to profiler-output file.

AUTOLOAD

When Devel::DProf finds a call to an &AUTOLOAD subroutine it looks at the $AUTOLOAD variable to find the real name of the sub being called. See Autoloading in perlsub.

ENVIRONMENT

PERL_DPROF_BUFFER sets size of output buffer in words. Defaults to 2**14.

PERL_DPROF_TICKS sets number of ticks per second on some systems where a replacement for times() is used. Defaults to the value of HZ macro.

PERL_DPROF_OUT_FILE_NAME sets the name of the output file. If not set, defaults to tmon.out.

BUGS

Builtin functions cannot be measured by Devel::DProf.

With a newer Perl DProf relies on the fact that the numeric slot of $DB::sub contains an address of a subroutine. Excessive manipulation of this variable may overwrite this slot, as in

  1. $DB::sub = 'current_sub';
  2. ...
  3. $addr = $DB::sub + 0;

will set this numeric slot to numeric value of the string current_sub , i.e., to 0 . This will cause a segfault on the exit from this subroutine. Note that the first assignment above does not change the numeric slot (it will mark it as invalid, but will not write over it).

Another problem is that if a subroutine exits using goto(LABEL), last(LABEL) or next(LABEL) then perl may crash or Devel::DProf will die with the error:

  1. panic: Devel::DProf inconsistent subroutine return

For example, this code will break under Devel::DProf:

  1. sub foo {
  2. last FOO;
  3. }
  4. FOO: {
  5. foo();
  6. }

A pattern like this is used by Test::More's skip() function, for example. See perldiag for more details.

Mail bug reports and feature requests to the perl5-porters mailing list at <perl5-porters@perl.org>.

SEE ALSO

perl, dprofpp, times(2)