Poor and inconsistent parallel performance scaling on Linux.

[Mysticial]

Parallel performance scaling is inconsistent on Linux. It does fairly well on 8-core Ryzen, but terribly on 10-core Skylake X.

While unconfirmed, it seems possible that the non-power-of-two cores doesn't play well with Linux.

It's a fact that y-cruncher has load balancing issues when the number of cores is not a power-of-two. But this isn't too much of an issue on Windows since the scheduler seems to do a fairly good job of time-slicing up the inbalances.

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Benchmarks: y-cruncher v0.7.4.9478

Single-threaded benchmarks are included as a baseline. The 1-2% difference between Windows and Linux for the single-threaded benchmarks is expected since different compilers were used. The important part is the parallel speedup.

Core i9 7900X (10 cores, 20 threads) @ 3.8 GHz AVX512, 3.0 GHz cache, 3800 MT/s memory

OS	Framework	Seconds	CPU Utilization	Speedup
Windows 10 (14393)	Single Threaded	295.773	5.00%	-
Windows 10 (14393)	Push Pool	32.598	87.05%	9.07x
Windows 10 (14393)	Cilk Plus	36.874	72.68%	8.02x
Ubuntu 17.04	Single Threaded	300.900	5.00%	-
Ubuntu 17.04	Push Pool	38.511	77.44%	7.81x
Ubuntu 17.04	Cilk Plus	34.923	86.25%	8.62x

Ryzen 7 1800X (8 cores, 16 threads) @ 3.8 GHz, 2666 MT/s memory

OS	Framework	Seconds	CPU Utilization	Speedup
Windows 10 (14393)	Single Threaded	671.752	6.25%	-
Windows 10 (14393)	Push Pool	85.321	93.64%	7.87x
Windows 10 (14393)	Cilk Plus	93.344	84.92%	7.20x
Ubuntu 17.04	Single Threaded	677.497	6.24%	-
Ubuntu 17.04	Push Pool	87.291	92.26%	7.76x
Ubuntu 17.04	Cilk Plus	89.820	94.68%	7.54x