Message-ID: <55BBA9D9.9030302@hp.com>
Date: Fri, 31 Jul 2015 13:01:13 -0400
From: Waiman Long <waiman.long@hp.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v3 1/7] locking/pvqspinlock: Unconditional PV kick with
 _Q_SLOW_VAL
References: <1437595962-21472-1-git-send-email-Waiman.Long@hp.com> <1437595962-21472-2-git-send-email-Waiman.Long@hp.com> <20150731083920.GD19282@twins.programming.kicks-ass.net>
In-Reply-To: <20150731083920.GD19282@twins.programming.kicks-ass.net>
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On 07/31/2015 04:39 AM, Peter Zijlstra wrote:
> On Wed, Jul 22, 2015 at 04:12:36PM -0400, Waiman Long wrote:
>> The smp_store_release() is not a full barrier. In order to avoid missed
>> wakeup, we may need to add memory barrier around locked and cpu state
>> variables adding to complexity. As the chance of spurious wakeup is very
>> low, it is easier and safer to just do an unconditional kick at unlock
>> time.
> This needs to better spell out the race; my still sleeping brain doesn't
> want to co-operate and its generally better to spell out these things
> anyway.

Sure, I will add a comment to talk about the possible race.

Cheers,
Longman
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