use Benchmark qw( timethese cmpthese );
use List::Util qw( shuffle );

for my $max (qw( 100 200 500 1000 2000 5000 )) {
    print "results for $max elems\n";

    my @big_list = shuffle 1 .. $max;

    cmpthese(
        -1,
        {   plain_sort => sub {
                my @local = sort { $b <=> $a } @big_list;
            },
            reversed => sub {
                my @local = reverse sort { $a <=> $b } @big_list;
            },
        }
    );

    print "\n";
}

exit 0;

__END__
results for 100 elems
              Rate plain_sort   reversed
plain_sort 46849/s         --        -8%
reversed   50717/s         8%         --

results for 200 elems
              Rate plain_sort   reversed
plain_sort 20676/s         --       -12%
reversed   23424/s        13%         --

results for 500 elems
             Rate plain_sort   reversed
plain_sort 7657/s         --        -9%
reversed   8374/s         9%         --

results for 1000 elems
             Rate plain_sort   reversed
plain_sort 3490/s         --        -8%
reversed   3794/s         9%         --

results for 2000 elems
             Rate plain_sort   reversed
plain_sort 1599/s         --        -9%
reversed   1756/s        10%         --

results for 5000 elems
            Rate plain_sort   reversed
plain_sort 553/s         --       -10%
reversed   613/s        11%         --