From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754596AbcDVRNz (ORCPT ); Fri, 22 Apr 2016 13:13:55 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:34759 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754474AbcDVRNy (ORCPT ); Fri, 22 Apr 2016 13:13:54 -0400 X-IBM-Helo: d03dlp01.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Fri, 22 Apr 2016 10:14:22 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Will Deacon , linux-kernel@vger.kernel.org Subject: Re: [PATCH] documentation: ACQUIRE applies to loads, RELEASE applies to stores Message-ID: <20160422171422.GF3756@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1461321709-16619-1-git-send-email-will.deacon@arm.com> <20160422143222.GU3430@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160422143222.GU3430@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16042217-8236-0000-0000-0000268E1FFD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 22, 2016 at 04:32:22PM +0200, Peter Zijlstra wrote: > On Fri, Apr 22, 2016 at 11:41:49AM +0100, Will Deacon wrote: > > For compound atomics performing both a load and a store operation, make > > it clear that _acquire and _release variants refer only to the load and > > store portions of compound atomic. For example, xchg_acquire is an xchg > > operation where the load takes on ACQUIRE semantics. > > > > Cc: Paul E. McKenney > > Thanks! > > Acked-by: Peter Zijlstra (Intel) Queued, thank you both! Thanx, Paul > > Signed-off-by: Will Deacon > > --- > > Documentation/memory-barriers.txt | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > > index 3729cbe60e41..05f8011011be 100644 > > --- a/Documentation/memory-barriers.txt > > +++ b/Documentation/memory-barriers.txt > > @@ -464,6 +464,11 @@ And a couple of implicit varieties: > > This means that ACQUIRE acts as a minimal "acquire" operation and > > RELEASE acts as a minimal "release" operation. > > > > +A subset of the atomic operations described in atomic_ops.txt have ACQUIRE > > +and RELEASE variants in addition to fully-ordered and relaxed (no barrier > > +semantics) definitions. For compound atomics performing both a load and a > > +store, ACQUIRE semantics apply only to the load and RELEASE semantics apply > > +only to the store portion of the operation. > > > > Memory barriers are only required where there's a possibility of interaction > > between two CPUs or between a CPU and a device. If it can be guaranteed that > > -- > > 2.1.4 > > >