use Benchmark qw( timethese );
my @files = glob "/bin/*";
timethese( -2, {
    Ordinary => sub {
        () = sort { -M $a <=> -M $b } @files
    },
    Schwartzian => sub {
        () = 
            map $_->[0],
            sort { $a->[1] <=> $b->[1] }
            map [ $_, -M ],
            @files;
        },
    },
);