The Benchmark::Forking module changes the behavior of the standard
Benchmark module, running each piece of code to be timed in a separate
forked process. Because each child exits after running its timing loop,
the computations it performs can't propogate back to affect subsequent
test cases.

This can make benchmark comparisons more accurate, because the
separate test cases are mostly isolated from side-effects caused by
the others. Benchmark scripts typically don't depend on those
side-effects, so in most cases you can simply use or require this
module at the top of your existing code without having to change
anything else.

WWW: http://search.cpan.org/dist/Benchmark-Forking/