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Date: Tue, 26 Nov 2013 06:49:59 -0800 From: Davidlohr Bueso <davidlohr@...com> To: Peter Zijlstra <peterz@...radead.org> Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>, Jason Low <jason.low2@...com>, Darren Hart <dvhart@...ux.intel.com>, Mike Galbraith <efault@....de>, Jeff Mahoney <jeffm@...e.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Scott Norton <scott.norton@...com>, Tom Vaden <tom.vaden@...com>, Aswin Chandramouleeswaran <aswin@...com>, Waiman Long <Waiman.Long@...com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake() On Tue, 2013-11-26 at 12:56 +0100, 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? That would be nthread mfence calls. > > 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. Right, but those particular numbers do not measure that path. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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