use Benchmark 'cmpthese';
for $size (2, 200, 20_000) {
    $s = "." x $len;
    print "\nDATASIZE = $size\n";
    cmpthese -5,{
        chop2   => '$t = $s; chop $t; chop $t;',
        subs    => '($t = $s) =~ s/..\Z//s;',
        lsubstr => '$t = $s; substr($t, -2) = "";',
        rsubstr => '$t = substr($s, 0, length($s)-2);',
    };
}