I have nothing to add to liverpole's suggestion, but the way you're doing your benchmark test. There's a Benchmark module available, which is really easy to use. If you write a benchmark code with it once, you'll never write a time calculation again. It is useful to compare results too.

Here is a code that compares liverpole's suggestion and the way you tried it first:

use strict;
use warnings;

use Benchmark qw(:all);

my $limit = 1_000;

sub do_it_tcarmeli {
    my %do_it_tcarmeli;
    foreach my $i ( 0 .. $limit ) {
        $do_it_tcarmeli{$i} = 1;
    }
    return;
}

my %do_it_liverpole;

sub do_it_liverpole {
    foreach my $i ( 0 .. $limit ) {
        $do_it_liverpole{$i} = 1;
    }
    return;
}

cmpthese(
    -10,
    {
        do_it_tcarmeli  => \&do_it_tcarmeli,
        do_it_liverpole => \&do_it_liverpole,
    }
);
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