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> <file>:<line>:<text>

where <num> is the number of times that the line was executed, <time> is the amount of time spent executing it and <file>, <line> and <text> are the filename, 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 -nrk 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 timings are made with "wall time" (time in real life vs. cpu usage). I'd like eventually to report cpu time, but that isn't terribly easy to get across platforms.

  • 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 except for the Win32 version which depends on Win32::API.


SmallProf has 3 variables which can be used during your script to affect what gets profiled.

  • 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.

  • 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 );
  • 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).


Just the usual

        perl Makefile.PL
        make test
        make install

and should install fine via the CPAN module. Makefile.PL checks to see if this is a Win32 platform and runs a conversion subroutine on SmallProf prior to installation.


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.

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


Ted Ashton <>

SmallProf was developed from code originally posted to usenet by Philippe Verdret <>. Special thanks to Geoffrey Broadwell <> for the Win32 code.

Copyright (c) 1997 Ted Ashton

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


Devel::DProf, Time::HiRes, Win32::API