Devel::DProf - a Perl code profiler

        perl -d:DProf test.pl

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:

        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:

        dprofpp

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

        dprofpp -T

Consult dprofpp for other options.

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

        #fOrTyTwO
        $hz=100;
        $XS_VERSION='DProf 19970606';
        # All values are given in HZ
        $rrun_utime=2; $rrun_stime=0; $rrun_rtime=7
        PART2
        + 26 28 566822884 DynaLoader::import
        - 26 28 566822884 DynaLoader::import
        + 27 28 566822885 main::bar
        - 27 28 566822886 main::bar
        + 27 28 566822886 main::baz
        + 27 28 566822887 main::bar
        - 27 28 566822888 main::bar
        [....]

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:

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

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

        #fOrTyTwO
        $hz=10000;
        $XS_VERSION='DProf 19971213';
        # All values are given in HZ
        $over_utime=5917; $over_stime=0; $over_rtime=5917;
        $over_tests=10000;
        $rrun_utime=1284; $rrun_stime=0; $rrun_rtime=1284;
        $total_marks=6;

        PART2
        @ 406 0 406
        & 2 main bar
        + 2
        @ 456 0 456
        - 2
        @ 1 0 1
        & 3 main baz
        + 3
        @ 141 0 141
        + 2
        @ 141 0 141
        - 2
        @ 1 0 1
        & 4 main foo
        + 4
        @ 142 0 142
        + & Devel::DProf::write
        @ 5 0 5
        - & Devel::DProf::write

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

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

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

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

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

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

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

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

Builtin functions cannot be measured by Devel::DProf.

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

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

will set this numeric slot to numeric value of the string CWcurrent_sub, i.e., to CW0. 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:

   panic: Devel::DProf inconsistent subroutine return

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

   sub foo {
     last FOO;
   }
   FOO: {
     foo();
   }

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>.

perl, dprofpp, times(2)