(This is the official perlfaq answer, minus any subsequent edits)
The Devel namespace has several modules which you can use to
profile your Perl programs. The Devel::DProf module comes with Perl and you can invoke it with the -d switch:
$ perl -d:DProf program.pl
After running your program under DProf, you’ll get a tmon.out file
with the profile data. To look at the data, you can turn it into a
human-readable report with the dprofpp program that comes with
Devel::DProf:
$ dprofpp
You can also do the profiling and reporting in one step with the -p
switch to dprofpp:
$ dprofpp -p program.pl
The Devel::NYTProf (New York Times Profiler) does both statement and subroutine profiling. It’s available from CPAN and you also invoke
it with the -d switch:
$ perl -d:NYTProf some_perl.pl
Like DProf, it creates a database of the profile information that you
can turn into reports. The nytprofhtml command turns the data into
an HTML report similar to the Devel::Cover report:
$ nytprofhtml
CPAN has several other profilers that you can invoke in the same
fashion. You might also be interested in using the C to
measure and compare code snippets.
You can read more about profiling in Programming Perl, chapter 20,
or Mastering Perl, chapter 5.
perldebguts documents creating a custom debugger if you need to
create a special sort of profiler. brian d foy describes the process
in The Perl Journal, “Creating a Perl Debugger”, and “Profiling in Perl”.
Perl.com has two interesting articles on profiling: “Profiling Perl”,
by Simon Cozens, and “Debugging and
Profiling mod_perl Applications”, by Frank Wiles.
Randal L. Schwartz writes about profiling in “Speeding up Your Perl
Programs” for Unix Review and “Profiling
in Template Toolkit via Overriding” for Linux Magazine.