v4.1.x: gcc_builtin: fix performance regression on x86_64 #8623
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in order to work around a bug in older gcc versions on x86_64, __atomic_thread_fence (__ATOMIC_SEQ_CST) was replaced with __atomic_thread_fence (__ATOMIC_ACQUIRE) based on the asumption that this did not introduce performance regressions. It was recently found that this did introduce some performance regression, mainly at scale on fat nodes. So simply use an asm memory globber to both workaround older gcc bugs and fix the performance regression. Thanks S. Biplab Raut for bringing this issue to our attention. Refs. open-mpi#8603 Signed-off-by: Gilles Gouaillardet <[email protected]> (cherry picked from commit d7e3f87)
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Merge by proxy from the other release branches, and from discussion on the 16 Mar 2021 Webex.
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in order to work around a bug in older gcc versions on x86_64,
__atomic_thread_fence (__ATOMIC_SEQ_CST)
was replaced with
__atomic_thread_fence (__ATOMIC_ACQUIRE)
based on the asumption that this did not introduce performance regressions.
It was recently found that this did introduce some performance regression,
mainly at scale on fat nodes.
So simply use an asm memory globber to both workaround older gcc bugs
and fix the performance regression.
Thanks S. Biplab Raut for bringing this issue to our attention.
Refs. #8603
Signed-off-by: Gilles Gouaillardet [email protected]
(cherry picked from commit d7e3f87)