[libcxx-commits] [PATCH] D69314: Bug fix for PR#43703

Ryan Prichard via Phabricator via libcxx-commits libcxx-commits at lists.llvm.org
Fri Mar 27 21:28:17 PDT 2020

rprichard added a comment.

In D69314#1941495 <https://reviews.llvm.org/D69314#1941495>, @ldionne wrote:

> @rprichard  Thanks for testing this on Windows. Do you think it's possible to make that test program run for a shorter amount of time so that it can be added to our test suite (i.e. do you think the test would still be relevant if we made it run for a shorter amount of time)?

I suppose a test would only need to sleep for a second or two total to exercise the new part1-vs-part2 logic. I'm not sure how much of the existing test would still be relevant.

Can the computation be split out from the Query calls, though? If we had an internal (Freq, Counter) -> time_point function, we could test that quickly.

I think this function assumes that the performance counter frequency is less than about `2**63 / 10**9`, about 9.22GHz. It was 10MHz on the two targets I saw, but comments on the Internet suggest that it's sometimes 3MHz <https://answers.microsoft.com/en-us/windows/forum/all/queryperformancefrequency-qpc-is-10-mhz-since/d0fb399d-5dfd-4a7a-af5f-220751953ad0>. I think this assumption is OK.

  rCXX libc++



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