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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Davidlohr Bueso <davidlohr@hp.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Jason Low <jason.low2@hp.com>,
	Darren Hart <dvhart@linux.intel.com>,
	Mike Galbraith <efault@gmx.de>, Jeff Mahoney <jeffm@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Scott Norton <scott.norton@hp.com>, Tom Vaden <tom.vaden@hp.com>,
	Aswin Chandramouleeswaran <aswin@hp.com>,
	Waiman Long <Waiman.Long@hp.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake()
Date: Tue, 26 Nov 2013 13:34:37 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.02.1311261333101.30673@ionos.tec.linutronix.de> (raw)
In-Reply-To: <20131126115628.GK10022@twins.programming.kicks-ass.net>

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

  reply	other threads:[~2013-11-26 12:34 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-25 20:58 Thomas Gleixner
2013-11-25 20:58 ` [RFC patch 1/5] futex: Misc cleanups Thomas Gleixner
2013-11-25 20:58 ` [RFC patch 2/5] futex: Document ordering guarantees Thomas Gleixner
2013-11-25 20:58 ` [RFC patch 3/5] futex: Split out unlock from queue_me() Thomas Gleixner
2013-11-25 20:58 ` [RFC patch 4/5] futex: Enqueue waiter before user space check Thomas Gleixner
2013-11-26  0:20   ` Darren Hart
2013-11-25 20:58 ` [RFC patch 5/5] futex: Allow lockless empty check of hash bucket plist Thomas Gleixner
2013-11-26  8:12 ` [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake() Davidlohr Bueso
2013-11-26  8:52   ` Peter Zijlstra
2013-11-26 11:21     ` Ingo Molnar
2013-11-26 11:56       ` Peter Zijlstra
2013-11-26 12:34         ` Thomas Gleixner [this message]
2013-11-26 15:38           ` Davidlohr Bueso
2013-11-26 14:49         ` Davidlohr Bueso
2013-11-26 19:25     ` Davidlohr Bueso
2013-11-26 20:51       ` Davidlohr Bueso
2013-11-26 23:56         ` Thomas Gleixner
2013-11-28  7:44           ` Davidlohr Bueso
2013-11-28 11:58             ` Thomas Gleixner
2013-11-28 11:59             ` Peter Zijlstra
2013-11-28 14:23               ` Thomas Gleixner
2013-12-01  4:37               ` Davidlohr Bueso
2013-12-02 11:01                 ` Thomas Gleixner
2013-12-01 12:10               ` Ingo Molnar
2013-12-01 12:56                 ` Peter Zijlstra
2013-12-01 16:55                   ` Ingo Molnar
2013-12-01 18:58                     ` Linus Torvalds
2013-12-01 20:39                       ` Eric Dumazet
2013-12-01 21:46                         ` Linus Torvalds
2013-12-03 17:59                           ` Darren Hart
2013-12-02 12:35                       ` Ingo Molnar

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