IMHE (In My Humble Experience), the sub based profilers often tell you what you already know, i.e. one particular sub is to blame. I found Devel::FastProf a line based profiler, very useful. It gives you information on what parts of the evil sub are the real performance killers. You use fprofpp to read the profile information.

Example output

# fprofpp output format is:
# filename:line time count: source
test_index.pl:567 7.33688 4248810: next LINE;
test_index.pl:100 0.02172 10231: sub trim
test_index.pl:154 0.02120 10230: sub rm_cmnts {
test_index.pl:468 0.02108 6138: $KEYWORDS[$i]{'max_width'} = length($v
+alue);
test_index.pl:373 0.01980 7411: return unless (!(-d $_));
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This also gives you useful debugging information, i.e. a certain line of code is executed less/more often than anticipated. So in practice I combine DProf and FastProf.

However... then I read about Devel::NYTProf, as suggested by missingthepoint above. It seems to combine the best of both DProf and FastProf and on top of that has tons of extra features. Well, that’s the next one on my TO DO list...