linux-kernel - Re: [RFC v2 3/7] powerpc: atomic: Implement atomic{,64}_{add,sub}_return

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Message-ID: <20150918165902.GF12837@arm.com>
Date:	Fri, 18 Sep 2015 17:59:02 +0100
From:	Will Deacon <will.deacon@....com>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>
Subject: Re: [RFC v2 3/7] powerpc: atomic: Implement
 atomic{,64}_{add,sub}_return_* variants

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
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