Add Windows support for CPU affinity for >64 CPUs. #817
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On supported Windows platforms (Win11 or Server 2022), use newer APIs to set CPU affinity correctly when there are more than 64 logical CPUs. Fixes /Disservin#816.
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Note I built the Windows binary using: And the toolchain was installed from the msys2 shell using: I'm not sure if the current Github workflow is configured correctly to use the UCRT. If building with a toolchain targeting an older Windows C runtime, the changes may fail to compile due to If a maintainer approves the workflow run, I guess we will see. |
Disservin
reviewed
Mar 16, 2025
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Wow! Thanks a lot for diagnosing this and fixing it :D |
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thanks! |
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On supported Windows platforms (Win11 or Server 2022), use newer APIs to set CPU affinity correctly when there are more than 64 logical CPUs.
Resolves #816, at least for those newer Windows platforms.
With this change, running concurrency 64 on a 7980X (64 cores, 128 SMT threads) on Windows 11 and enabling CPU affinity now results in the expected CPU utilization:
As you can see, the first logical CPU of each of the 64 physical cores is now being utilized. This results in better and more consistent performance.
I've also validated that the app still works on Windows 10 (where
SetProcessDefaultCpuSetMasksis not available), both with and without setting CPU affinity. Note that the Windows 10 system is a 4 core / 8 thread machine. I don't think testing on a >64 thread Windows 10 system is required.