[PATCH] D85531: [SystemZ/ZOS] Add support for getHostNumPhysicalCores()

Mon Aug 10 07:56:26 PDT 2020

aganea added inline comments.

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Comment at: llvm/lib/Support/Host.cpp:1334
+      static_cast<uintptr_t>(reinterpret_cast<unsigned int &>(CVT[CVTCSD])));
+  return reinterpret_cast<int &>(CSD[CSD_NUMBER_ONLINE_STANDARD_CPS]);
+}
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hubert.reinterpretcast wrote:
> Kai wrote:
> > MaskRay wrote:
> > > If z/OS supports something similar to `taskset -c 0-3 $program`, make sure the function returns a number less than or equal to 4. 
> > Thanks for the hint. This kind of command is not supported on z/OS.
> > The reason is the fault tolerance available in z/OS: if a defect in a CP is detected, then this CP can go offline and a spare CP can continue to run the code exactly at the point where the former CP went offline. This does not work if the process is tied to a certain set of CPs, and therefore it's not supported.
> @MaskRay, I think the test you propose imposes an additional restriction that I am not sure the existing implementations of the function adhere to. Namely, I believe the test that you proposed indicates that the intent is to return a number that is one greater than the highest processor index number on the system. I think this might differ from the count of available processors. My understanding is that the function is meant to return the latter.
@hubert.reinterpretcast Actually both the Linux & Windows implementations return the restricted set of CPUs/processors that are usable within the process (ie. CPUs represented by the affinity mask).
https://github.com/llvm/llvm-project/blob/62a933b72c5b060bcb2c7332d05082f002d6c65a/llvm/lib/Support/Host.cpp#L1234

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https://reviews.llvm.org/D85531