Salvador Fandiño García


Devel::SmallProf - per-line Perl profiler


        perl5 -d:SmallProf


The Devel::SmallProf profiler is focused on the time taken for a program run on a line-by-line basis. It is intended to be as "small" in terms of impact on the speed and memory usage of the profiled program as possible and also in terms of being simple to use. Those statistics are placed in the file smallprof.out in the following format:

        <num> <time> <ctime> <line>:<text>

where <num> is the number of times that the line was executed, <time> is the amount of "wall time" (time according the the clock on the wall vs. cpu time) spent executing it, <ctime> is the amount of cpu time expended on it and <line> and <text> are the line number and the actual text of the executed line (read from the file).

The package uses the debugging hooks in Perl and thus needs the -d switch, so to profile, use the command:

        perl5 -d:SmallProf

Once the script is done, the statistics in smallprof.out can be sorted to show which lines took the most time. The output can be sorted to find which lines take the longest, either with the sort command:

        sort -k 2nr,2 smallprof.out | less

or a perl script:

        @sorted = sort {(split(/\s+/,$b))[2] <=> 
                        (split(/\s+/,$a))[2]} <PROF>;
        close PROF;
        print join('',@sorted);


  • The "wall time" readings come from Time::HiRes and are reasonably useful, at least on my system. The cpu times come from the 'times' built-in and the granularity is not necessarily as small as with the wall time. On some systems this column may be useful. On others it may not.

  • SmallProf does attempt to make up for its shortcomings by subtracting a small amount from each timing (null time compensation). This should help somewhat with the accuracy.

  • SmallProf depends on the Time::HiRes package to do its timings. It claims to require version 1.20, but may work with earlier versions, depending on your platform.


SmallProf has 4 variables which can be used during your script to affect what gets profiled.

$DB::drop_zeros (z)

If you do not wish to see lines which were never called, set the variable $DB::drop_zeros = 1. With drop_zeros set, SmallProf can be used for basic coverage analysis.

$DB::profile (p)

To turn off profiling for a time, insert a $DB::profile = 0 into your code (profiling may be turned back on with $DB::profile = 1). All of the time between profiling being turned off and back on again will be lumped together and reported on the $DB::profile = 0 line. This can be used to summarize a subroutine call or a chunk of code.


To only profile code in a certain package, set the %DB::packages array. For example, to see only the code in packages main and Test1, do this:

        %DB::packages = ( 'main' => 1, 'Test1' => 1 );
$DB::grep_format (g)

Generates output on a format similar to grep easily parseable from tools like Emacs (see below).

grep format output appears as:

  file name : line num : count : time : ctime : source


  file name : line num : count : time : ctime : (eval n: line num) source

for code inside evals.

Times appear in miliseconds.

These variables can be put in a file called .smallprof in the current directory. For example, a .smallprof containing

        $DB::drop_zeros = 1;
        $DB::profile = 0;

will set SmallProf to not report lines which are never touched for any file profiled in that directory and will set profiling off initially (presumably to be turned on only for a small portion of code).

Environment variable SMALLPROF_CONFIG can be also used to set those flags, i.e:

   SMALLPROF_CONFIG=zg perl -d:SmallProf my_script.plx

activates drop_zeros and grep_format modes.


Just the usual

        perl Makefile.PL
        make test
        make install

and should install fine via the CPAN module.


Subroutine calls are currently not under the control of %DB::packages. This should not be a great inconvenience in general.

The handling of evals is bad news. This is due to Perl's handling of evals under the -d flag. For certain evals, caller() returns '(eval n)' for the filename and for others it doesn't. For some of those which it does, the array @{'_<filename'} contains the code of the eval. For others it doesn't. Sometime, when I've an extra tuit or two, I'll figure out why and how I can compensate for this. (Note: 5.6.0 made some debugging changes. This may now be fixed, I'm not sure).

SmallProf must be invoked from the command line. If it is included on the shebang line, the file in which it is included will not be visible in the symbol table. Profiling will continue as expected, but the contents of the source lines will not be listed. This is new as of 5.6.0.

Comments, advice and questions are welcome. If you see inefficent stuff in this module and have a better way, please let me know.


  1. Use the DB::grep_format flag to turn on grep like format, i.e.

      SMALLPROF_CONFIG=g perl -d:SmallProf
  2. Tell Emacs/XEmacs to read smallprof.out as grep output:

      M-x grep RET C-a C-k cat smallprof.out RET
  3. Point and click to go to the script hot spots!


Devel::SmallProf was developed by Ted Ashton <>. It is currently being maintained by Salvador Fandiño <>.

SmallProf was developed from code originally posted to usenet by Philippe Verdret <>. Special thanks to Geoffrey Broadwell <> for his assistance on the Win32 platform and to Philippe for his patient assistance in testing and debugging.


Copyright (c) 1997-2000 Ted Ashton

Copyright (c) 2003-2007 Salvador Fandiño

This module is free software and can be redistributed and/or modified under the same terms as Perl itself.


Devel::FastProf is a simplified and much faster version of this module.

Devel::DProf, Time::HiRes.

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