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Date: Tue, 13 Oct 2015 14:24:04 +0100
From: Will Deacon <will.deacon@arm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Waiman Long <waiman.long@hp.com>, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v3 6/6] powerpc: atomic: Implement cmpxchg{,64}_* and
 atomic{,64}_cmpxchg_* variants
Message-ID: <20151013132404.GI21550@arm.com>
References: <1444659246-24769-1-git-send-email-boqun.feng@gmail.com>
 <1444659246-24769-7-git-send-email-boqun.feng@gmail.com>
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On Mon, Oct 12, 2015 at 10:14:06PM +0800, Boqun Feng wrote:
> Implement cmpxchg{,64}_relaxed and atomic{,64}_cmpxchg_relaxed, based on
> which _release variants can be built.
> 
> To avoid superfluous barriers in _acquire variants, we implement these
> operations with assembly code rather use __atomic_op_acquire() to build
> them automatically.

The "superfluous barriers" are for the case where the cmpxchg fails, right?
And you don't do the same thing for release, because you want to avoid a
barrier in the middle of the critical section?

(just checking I understand your reasoning).

Will