A nulltime compensation is effective when the overhead is relatively small compared to the sentence execution time. But when it is much bigger as in this case, the compensated overhead (aka error) can still be of the same order of magnitude of the time we want to measure.

Guess why the last line you have quoted from the source is there!

package DB;

use Time::HiRes;

my %testDB = ( null => sub {
                   my($pkg,$filename,$line) = caller;
                   $profile || return;
                   %packages && !$packages{$pkg} && return;
               },
               work => sub {
                   $do_something{foo} = 'bar';
                   my($pkg,$filename,$line) = caller;
                   $profile || return;
                   %packages && !$packages{$pkg} && return;
               });



my $n = 10;
for (1..$n) {
    for my $t (keys %testDB) {
        my $testDB = $testDB{$t};
        my $nulltime = 0;
        for (1..100) {
            my($u,$s,$cu,$cs) = times;
            $cstart = $u+$s+$cu+$cs;
            $start = Time::HiRes::time;
            &$testDB;
            ($u,$s,$cu,$cs) = times;
            $cdone = $u+$s+$cu+$cs;
            $done = Time::HiRes::time;
            $diff = $done - $start;
            $nulltime += $diff;
        }
        $time{$t} = $nulltime / 100 * 1e6;
    }
    printf "null: %.2f, work: %.2f, delta: %.2f\n",
        $time{null}, $time{work}, $time{work} - $time{null};
}
[download]

I get this output from your code. Is that good, bad or ugly?

null: 6.63, work: 7.41, delta: 0.77
null: 6.45, work: 7.60, delta: 1.14
null: 6.41, work: 7.36, delta: 0.95
null: 6.49, work: 7.25, delta: 0.77
null: 6.47, work: 7.41, delta: 0.93
null: 6.52, work: 7.37, delta: 0.85
null: 6.38, work: 7.30, delta: 0.93
null: 6.44, work: 7.22, delta: 0.78
null: 6.49, work: 7.38, delta: 0.89
null: 6.50, work: 7.29, delta: 0.79
[download]

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

Well, it seems that on your system the output is pretty consistent as all the delta values are very similar. On my computer it generates a broader range of values:

null: 4.34, work: 4.53, delta: 0.19
null: 4.70, work: 4.67, delta: -0.03
null: 5.33, work: 6.38, delta: 1.05
null: 4.83, work: 6.05, delta: 1.22
null: 4.68, work: 5.27, delta: 0.58
null: 6.56, work: 5.12, delta: -1.44
null: 4.42, work: 9.26, delta: 4.85
null: 5.26, work: 4.58, delta: -0.68
null: 6.63, work: 5.86, delta: -0.78
null: 4.34, work: 7.54, delta: 3.20
[download]