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Fix Thread.GetCurrentProcessorId for > 64 CPUs on Windows. #581

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VSadov merged 1 commit into from
Dec 6, 2019
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Fix Thread.GetCurrentProcessorId for > 64 CPUs on Windows. #581

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6 changes: 6 additions & 0 deletions src/coreclr/src/vm/comsynchronizable.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1450,6 +1450,12 @@ FCIMPL0(INT32, ThreadNative::GetCurrentProcessorNumber)
{
FCALL_CONTRACT;

#ifndef FEATURE_PAL
PROCESSOR_NUMBER proc_no_cpu_group;
GetCurrentProcessorNumberEx(&proc_no_cpu_group);
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@sergiy-k sergiy-k Dec 5, 2019

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Is it OK if ThreadNative::GetCurrentProcessorNumber might return an index that is larger than total number of active processors on the system?

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@VSadov VSadov Dec 5, 2019 •
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Yes. What we return to the user is technically “ID correlated with last core we ran on”. We may even default to ThreadID if OS API is not functional. (PAL may return -1).

Are process groups contiguous? (1,2,3, ...)

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@VSadov VSadov Dec 5, 2019

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To answer my question - yes, OS "packs" cores into as few process groups as possible and considers topology when assigning.
https://docs.microsoft.com/en-us/windows/win32/procthread/processor-groups

return (proc_no_cpu_group.Group << 6) | proc_no_cpu_group.Number;
#else
return ::GetCurrentProcessorNumber();
#endif //!FEATURE_PAL
}
FCIMPLEND;