my $size = 10000;
my $cpus = MCE::Util->get_ncpu() || 4;
MCE::Loop::init { max_workers => $cpus, chunk_size => $size };
our $max = scalar keys %barcode_hash;
sub haukex {
    our %barcode_hash;
    our $barcode_pair_35;
    our $max;
    for ( 1.. $max ) {
        1 if $barcode_hash{$_}[2] eq $barcode_pair_35;
    }
}

sub karl {
    our %barcode_hash;
    our $barcode_pair_35;
    our $max;
    mce_loop {
        my ( $mce, $chunk_ref, $chunk_id ) = @_;
        for (@$chunk_ref) {
            1 if ( $barcode_hash{$_}[2] eq $barcode_pair_35 );
        }
    }
    1..$max;
}

haukex 2.29/s     --   -38%
karl   3.67/s    60%     --