Messages in this thread | | | Date | Tue, 26 Nov 2013 13:34:37 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake() |
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On Tue, 26 Nov 2013, Peter Zijlstra wrote:
> On Tue, Nov 26, 2013 at 12:21:40PM +0100, Ingo Molnar wrote: > > I'm somewhat reluctant to chalk it up to a single mfence - maybe > > timings/behavior changed in some substantial way? > > Ah indeed! We also changed the case where an enqueueing futex sees the > uval change and bails. It is now far more expensive due to having to > both queue and unqueue, whereas before it wouldn't queue at all. > > I suppose the idea was to offset that by not requiring locking on the > wake side.
Aside of that I really would be interrested in an explanation for the STDDEV going up by factor 5. That's a clear indicator for fishyness.
Thanks,
tglx
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