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Sebastian Andrzej Siewior
9a57c37731
Chris Mason reported a performance regression on big iron. Reports of this kind were usually reported as part of a micro benchmark but Chris' test did mimic his real workload. This makes it a real regression. The root cause is rcuref_get() which is invoked during each futex operation. If all threads of an application do this simultaneously then it leads to cache line bouncing and the performance drops. Disable FUTEX_PRIVATE_HASH entirely for this cycle. The performance regression will be addressed in the following cycle enabling the option again. Closes: https://lore.kernel.org/all/[email protected]/ Reported-by: Chris Mason <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Link: https://lkml.kernel.org/r/[email protected]