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Forcibly split NUMA nodes on Windows

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split by processor groups due to Window's thread scheduler issues.

fixes #5551
closes https://github.com/official-stockfish/Stockfish/pull/5552

No functional change
This commit is contained in:
Tomasz Sobczyk
2024-08-26 15:22:22 +02:00
committed by Joost VandeVondele
parent 9fb58328e3
commit a0597b1281
1 changed files with 15 additions and 1 deletions
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16
src/numa.h
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@@ -582,7 +582,21 @@ class NumaConfig {
// still no way to set thread affinity spanning multiple processor groups.
// See https://learn.microsoft.com/en-us/windows/win32/procthread/numa-support
// We also do this is if need to force old API for some reason.
if (STARTUP_USE_OLD_AFFINITY_API)
//
// 2024-08-26: It appears that we need to actually always force this behaviour.
// While Windows allows this to work now, such assignments have bad interaction
// with the scheduler - in particular it still prefers scheduling on the thread's
// "primary" node, even if it means scheduling SMT processors first.
// See https://github.com/official-stockfish/Stockfish/issues/5551
// See https://learn.microsoft.com/en-us/windows/win32/procthread/processor-groups
//
// Each process is assigned a primary group at creation, and by default all
// of its threads' primary group is the same. Each thread's ideal processor
// is in the thread's primary group, so threads will preferentially be
// scheduled to processors on their primary group, but they are able to
// be scheduled to processors on any other group.
//
// used to be guarded by if (STARTUP_USE_OLD_AFFINITY_API)
{
NumaConfig splitCfg = empty();