[Kailee71]

HP Z840, 2x Xeon E5-2637v4, 2x4 cores, 3.5GHz, 128Gb 2400Mhz in 8x16Gb, single rank.

Threads   Mesh    Speedup Runtime Speedup It/s
1         1581    1       1048.83 1.00    0.1
2         1042    1.52    525.38  1.99    0.19
4         570     2.77    224.17  4.68    0.45
6         400     3.95    159.36  6.58    0.63
8         332     4.76    133.11  7.88    0.75

Does someone have an explanation for the super-linear speedups on the runtimes?


Those cpus still have 4 memory channels, which usually form the bottleneck but might be underused by 1 thread/memory channel, so just out of curiosity...

Threads   Mesh    Speedup Runtime Speedup It/s
10        449     3.52    157.40  6.66    .64
12        376     4.20    146.59  7.15    .68
14        354     4.47    130.91  8.01    .76
16        337     4.69    125.14  8.38    .80

... Interesting ... But still not worth using threads vs. cores.

K.