NAME¶
Devel::DProf - a DEPRECATED Perl code profiler
SYNOPSIS¶
perl -d:DProf test.pl
ACHTUNG!¶
"Devel::DProf" is
DEPRECATED and will be removed from a future
version of Perl. We strongly recommend that you install and use Devel::NYTProf
instead, as it offers significantly improved profiling and reporting.
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:
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 $ENV{PERL_DPROF_TICKS}).
New "$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.
Lines starting with "@" mark the amount of time passed since the
previous "@" line. The numbers following the "@" are
integer tick counts representing user, system, and real time. Divide these
numbers by the $hz value in the header to get seconds.
Lines starting with "&" map subroutine identifiers (an integer) to
subroutine packages and names. These should only occur once per subroutine.
Lines starting with "+" or "-" mark normal entering and exit
of subroutines. The number following is a reference to a subroutine
identifier.
Lines starting with "*" mark where subroutines are entered by
"goto &subr", but note that the return will still be marked as
coming from the original sub. The sequence might look like this:
+ 5
* 6
- 5
Lines starting with "/" is like "-" but mark where
subroutines are exited by dying. Example:
+ 5
+ 6
/ 6
/ 5
Finally you might find "@" time stamp marks surrounded by "+
& Devel::DProf::write" and "- & Devel::DProf::write"
lines. These 3 lines are outputted when printing of the mark above actually
consumed measurable time.
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
"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:
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.
SEE ALSO¶
perl, dprofpp,
times(2)