opal/fifo: fix 128-bit atomic fifo on Power9 #5374
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@jsquyres Turns out that Power 9 can support 128-bit compare-exchange. It has LL/SC instructions for reading/writing quad words. |
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FYI @gpaulsen. Targeted for v3.0.x and v3.1.x. |
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Our CI is power8, but I think Josh disabled make-check. |
This commit updates the atomic fifo code to fix a consistency issue observed on Power9 systems when builtin atomics are used. The cause was two things: 1) a missing write memory barrier in fifo push, and 2) a read ordering issue when reading the fifo head non-atomically. This commit fixes both issues and appears to correct then inconsistency. Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
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@gpaulsen Any news? 😄 |
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I'll give it a go. |
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Build and runs fine on power8 and power9, both with RHEL 7.5 and gcc 4.8.5 'make check' reported all PASSES (including opal_fifo). NOTE: mpool_memkind was skipped because configure was not able to build it (no memkind.h at configure time). I assume this is not related to this opal_fifo change. Thanks again @hjelmn |
gpaulsen
approved these changes
Jul 10, 2018
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This commit updates the atomic fifo code to fix a consistency issue
observed on Power9 systems when builtin atomics are used. The cause
was two things: 1) a missing write memory barrier in fifo push, and 2)
a read ordering issue when reading the fifo head non-atomically. This
commit fixes both issues and appears to correct then inconsistency.
Signed-off-by: Nathan Hjelm hjelmn@lanl.gov