linux-kernel - Re: [PATCH 2/3 v2] futex: avoid double wake up in futex

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Date:	Sun, 12 Apr 2015 20:02:35 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Darren Hart <darren@...art.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	fredrik.markstrom@...driver.com,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH 2/3 v2] futex: avoid double wake up in futex_wake() on
 -RT

On Fri, 2015-04-10 at 18:11 +0200, Sebastian Andrzej Siewior wrote:
> This patch delays the wakeup of the process untill
						^^^ until

>  the hb->lock is
> dropped to avoid boosting + context switch to obtain the lock.

Doing the wakeups while holding the lock is also a general performance
issue for futex_wake. The problem being dealing with spurious wakeups
(wacky drivers), which makes no difference wrt nr_wake.

Thanks,
Davidlohr

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