linux-kernel - Re: [RFC PATCH 03/15] Provide atomic_t functions implemented with ISO-C++11 atomics

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Message-ID: <20160518173112.GD3206@twins.programming.kicks-ass.net>
Date:	Wed, 18 May 2016 19:31:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-arch@...r.kernel.org, x86@...nel.org, will.deacon@....com,
	linux-kernel@...r.kernel.org, ramana.radhakrishnan@....com,
	paulmck@...ux.vnet.ibm.com, dwmw2@...radead.org
Subject: Re: [RFC PATCH 03/15] Provide atomic_t functions implemented with
 ISO-C++11 atomics

On Wed, May 18, 2016 at 04:10:59PM +0100, David Howells wrote:
>      (b) An ISYNC instruction is emitted as the Acquire barrier with
>      	 __ATOMIC_SEQ_CST, but I'm not sure this is strong enough.
> 
>      (c) An LWSYNC instruction is emitted as the Release barrier with
>      	 __ATOMIC_ACQ_REL or __ATOMIC_RELEASE.  Is this strong enough that
>      	 we could use these memorders instead?

Our atomic acquire/release operations are RCpc, so yes. Our locks would
like to be RCsc but currently powerpc is an RCpc holdout there as well.