From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753149AbbG0KVI (ORCPT ); Mon, 27 Jul 2015 06:21:08 -0400 Received: from foss.arm.com ([217.140.101.70]:52150 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752103AbbG0KVF (ORCPT ); Mon, 27 Jul 2015 06:21:05 -0400 Date: Mon, 27 Jul 2015 11:21:07 +0100 From: Will Deacon To: Peter Zijlstra Cc: "linux-arch@vger.kernel.org" , "Waiman.Long@hp.com" , "linux-kernel@vger.kernel.org" , "paulmck@linux.vnet.ibm.com" Subject: Re: [PATCH v3 1/8] atomics: add acquire/release/relaxed variants of some atomic operations 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 Content-Disposition: inline In-Reply-To: <20150727091430.GP19282@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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