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Date: Fri, 18 Sep 2015 17:59:02 +0100
From: Will Deacon <will.deacon@arm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.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>
Subject: Re: [RFC v2 3/7] powerpc: atomic: Implement
 atomic{,64}_{add,sub}_return_* variants
Message-ID: <20150918165902.GF12837@arm.com>
References: <1442418575-12297-1-git-send-email-boqun.feng@gmail.com>
 <1442418575-12297-4-git-send-email-boqun.feng@gmail.com>
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Thread-Topic: [RFC v2 3/7] powerpc: atomic: Implement
 atomic{,64}_{add,sub}_return_* variants
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On Wed, Sep 16, 2015 at 04:49:31PM +0100, Boqun Feng wrote:
> On powerpc, we don't need a general memory barrier to achieve acquire and
> release semantics, so __atomic_op_{acquire,release} can be implemented
> using "lwsync" and "isync".

I'm assuming isync+ctrl isn't transitive, so we need to get to the bottom
of the s390 thread you linked me to before we start spreading this
further:

  https://lkml.org/lkml/2015/9/15/836

Will