fib.p6

sub fib($n) {
    $n <= 1 ?? 1 !! fib($n - 2) + fib($n - 1)
}

for 1..10 -> $degree {
    my $start = now;
    my @fibs = await (start { fib(25) }) xx $degree;
    say "$degree: {now - $start}";
    die "Oops!" unless [==] @fibs;
}

results

1: 1.0476326        # baseline cost
2: 1.1106408
3: 1.2746614
4: 1.30716571       # number of physical cores
5: 1.4821886
6: 1.6322063
7: 1.6427082
8: 1.9857531        # number of virtual cores
9: 3.262914
10: 3.3859285