From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v3 1/8] atomics: add acquire/release/relaxed variants of some atomic operations Date: Mon, 27 Jul 2015 11:21:07 +0100 Message-ID: <20150727102106.GD3358@arm.com> References: <1437746681-2809-1-git-send-email-will.deacon@arm.com> <1437746681-2809-2-git-send-email-will.deacon@arm.com> <20150727091430.GP19282@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150727091430.GP19282@twins.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: "linux-arch@vger.kernel.org" , "Waiman.Long@hp.com" , "linux-kernel@vger.kernel.org" , "paulmck@linux.vnet.ibm.com" List-Id: linux-arch.vger.kernel.org On Mon, Jul 27, 2015 at 10:14:30AM +0100, Peter Zijlstra wrote: > On Fri, Jul 24, 2015 at 03:04:34PM +0100, Will Deacon wrote: > > This patch introduces three new ordering semantics for these operations: > > > > - *_relaxed: No ordering guarantees. This is similar to what we have > > already for the non-return atomics (e.g. atomic_add). > > > > - *_acquire: ACQUIRE semantics, similar to smp_load_acquire. > > > > - *_release: RELEASE semantics, similar to smp_store_release. > > Do we want to further specify that for the RmW operations the Read/load > will provide the acquire and the Write/store the release? Yeah, that's not a bad idea, but if we add that then I probably need to re-iterate the cmpxchg strangeness since a failed cmpxchg_acquire would still not have barrier semantics with the current implementation even though it must have performed a Read/load access. Will