linux-kernel - Re: [PATCH 4/5] futex: Avoid taking hb lock if nothing to wakeup

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Message-ID: <20131125173811.GD10022@twins.programming.kicks-ass.net>
Date:	Mon, 25 Nov 2013 18:38:11 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mike Galbraith <efault@....de>, Jeff Mahoney <jeffm@...e.com>,
	"Norton, Scott J" <scott.norton@...com>, tom.vaden@...com,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	Waiman Long <Waiman.Long@...com>,
	Jason Low <jason.low2@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 4/5] futex: Avoid taking hb lock if nothing to wakeup

On Mon, Nov 25, 2013 at 06:32:55PM +0100, Thomas Gleixner wrote:
> In that context it would also be helpful to measure the overhead on
> x86 for the !empty case.

Yes, because mfence is by no means a cheap instruction on x86.
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