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Message-ID: <1428894155.16668.6.camel@stgolabs.net>
Subject: Re: [PATCH 2/3 v2] futex: avoid double wake up in futex_wake() on
 -RT
From: Davidlohr Bueso <dave@stgolabs.net>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Darren Hart <darren@dvhart.com>, Steven Rostedt <rostedt@goodmis.org>,
        fredrik.markstrom@windriver.com,
        Manfred Spraul <manfred@colorfullife.com>
Date: Sun, 12 Apr 2015 20:02:35 -0700
In-Reply-To: <20150410161135.GF3057@linutronix.de>
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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