Comment 81 for bug 1640518
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| William J. Schmidt (wschmidt-g) wrote | #81 |
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bbfa235
(Get the code!)
Hi Andrew,
This is a POWER-specific "optimization" that dates to last December (so it in fact wouldn't show up in Ubuntu 15.04 or 15.10, it appears). The decrement used to be attached to the lock rather than the unlock and it was apparently moved to the present location because it showed a good performance improvement. Aaron is running some experiments with moving it ahead of the unlock rather than following it, which we believe will remove the problem. That may or may not be the final version of the fix, but it looks like the simplest solution.
The only reason for you to test on a Skylake machine would be for your own peace of mind, in case any TLE-specific issues are hiding in the x86 implementation. This specific problem, at least, is a POWER issue.