std.parallelism unable to use more than 64 cores

[dlangBugzillaToGithub]

crayolist reported this on 2019-01-11T19:56:42Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=19577

Description

Currently std.parallelism.totalCPUs on Windows is implemented using the system call GetSystemInfo() which can return a maximum of 64 cores.
On a Xeon Phi 7250 system with 272 cores it is impossible to exploit all cores.

TBB (Threading building blocks) uses the Processor Groups to correctly identify all cores, like this;
https://github.com/01org/tbb/blob/314792356bf75f4a190277536aea543b9b6b310b/src/tbb/tbb_misc_ex.cpp#L241

A Xeon Phi 7250 which has 68 cores and 4 threads per core is reported as 5 Processor Groups; 4 x 64 cores + 1 x 16 cores.