multithread/concurrency/parallel methods and performance

[SrMordred]

I´m experimenting with threads and related recently.
(i´m just started so may be some terrrible mistakes here)

With this base work:

foreach(i ; 0 .. SIZE)
{
     results[i] = values1[i] * values2[i];
}

and then with this 3 others methods: parallel, spawn and Threads.

this was my results:

_base : 456 ms and 479 us
_parallel : 331 ms, 324 us, and 4 hnsecs
_concurrency : 367 ms, 348 us, and 2 hnsecs
_thread : 369 ms, 565 us, and 3 hnsecs

(code here : https://run.dlang.io/is/2pdmmk )

All methods have minor speedup gains.  I was expecting a lot more.
Since I have 7 cores I expected like below 100ms.

I´m not seeing false sharing in this case. or i'm wrong?

If someone can expand on this, i'll be grateful.

Thanks!