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Message-ID: <1437863509.3298.71.camel@stgolabs.net>
Subject: Re: [PATCH v3 1/7] locking/pvqspinlock: Unconditional PV kick with
 _Q_SLOW_VAL
From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, 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>
Date: Sat, 25 Jul 2015 15:31:49 -0700
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On Wed, 2015-07-22 at 16:12 -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.

Although I guess if SPIN_THRESHOLD is ever enlarged, the chances of
spurious wakeups would be greater.

> Signed-off-by: Waiman Long <Waiman.Long@hp.com>

Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>