Devel::DProf
Devel::DProf(3) Perl Programmers Reference Guide Devel::DProf(3)
NAME
Devel::DProf - a Perl code profiler
SYNOPSIS
perl5 -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 subrou-
tines 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:
perl5 -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 subrou-
tines 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.
PROFILE FORMAT
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 real-
time of the process while it was being profiled. The sixth line indi-
cates 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 $ENV{PERL_DPROF_TICKS}).
New "$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
$DB::sub = 'current_sub';
...
$addr = $DB::sub + 0;
will set this numeric slot to numeric value of the string "cur-
rent_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:
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 exam-
ple. 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)
perl v5.8.6 2001-09-21 Devel::DProf(3)
