Programming Perl, 4th Edition

Devel::DProf

Do you want to make your program faster? Well, of course you do. But first you should stop and ask yourself, “Do I really need to spend time making this program faster?” Recreational optimization can be fun,^[177] but normally there are better uses for your time. Sometimes you just need to plan ahead and start the program when you’re going on a coffee break (or use it as an excuse for one). But if your program absolutely must run faster, you should begin by profiling it. A profiler can tell you which parts of your program take the most time to execute, so you won’t waste time optimizing a subroutine that has an insignificant effect on the overall execution time.

Perl comes with a profiler, the Devel::DProf module. You can use it to profile the Perl program in mycode.pl by typing:

% perl –d:DProf mycode.pl

Even though we’ve called it a profiler—since that’s what it does—the mechanism DProf employs is the very same one we discussed earlier in this chapter. DProf is just a debugger that records the time Perl entered and left each subroutine.

When your profiled script terminates, DProf will dump the timing information to a file called tmon.out. The dprofpp program that came with Perl knows how to analyze tmon.out and produce a report. You may also use dprofpp as a frontend for the whole process with the –p switch (described later).

Given this program:

outer(); sub outer { for (my $i=0; $i < 100; $i++) { inner() } } sub inner { my $total = 0; for (my $i=0; $i < 1000; $i++) { $total ...