use strict;
use warnings;
use 5.010;
use threads;
use Time::HiRes qw(time);

my $data = 'x' x 500_000_000;
my $t    = time;
threads->create(
    sub {
        $data =~ tr/x/y/;
    }
)->join;
say time - $t;
__END__
1.29563307762146