[PATCH] D71775: [ThreadPool] On Windows, extend usage to all CPU sockets and all NUMA groups

[Nico Weber via Phabricator via cfe-commits]

thakis added a comment.

https://bugs.chromium.org/p/chromium/issues/detail?id=1051578#c12 :

"""
FYI for those building on AMD Bulldozer family of processors and its various iterations after this commit:

https://reviews.llvm.org/D71775

Building with ThinLTO on Bulldozer and similar appears to now be capped to how Windows reports cores versus logical processors, thus now halving the number of LTO threads available when building. Manually setting /opt:lldltojobs= for LLD does not override it, as that only sets an upper limit.

Found out as I locally build on a 32-core Opteron system. Windows treats it as 16 cores and 32 logical processors, but it is not a SMT setup like Intel HyperTreading. In particular:

"A module consists of a coupling of two "conventional" x86 out of order processing cores. The processing core shares the early pipeline stages (e.g. L1i, fetch, decode), the FPUs, and the L2 cache with the rest of the module."

https://en.wikipedia.org/wiki/Bulldozer_(microarchitecture)

Naturally, build times have increased dramatically. YMMV.
"""

Sounds like this patch might have some drawbacks.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71775/new/

https://reviews.llvm.org/D71775