From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oa0-f50.google.com (mail-oa0-f50.google.com [209.85.219.50]) by kanga.kvack.org (Postfix) with ESMTP id 52B186B0031 for ; Thu, 21 Nov 2013 08:17:03 -0500 (EST) Received: by mail-oa0-f50.google.com with SMTP id n16so2215438oag.23 for ; Thu, 21 Nov 2013 05:17:02 -0800 (PST) Received: from e32.co.us.ibm.com (e32.co.us.ibm.com. [32.97.110.150]) by mx.google.com with ESMTPS id u2si19417228oem.62.2013.11.21.05.17.01 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 21 Nov 2013 05:17:02 -0800 (PST) Received: from /spool/local by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 21 Nov 2013 06:17:01 -0700 Received: from b03cxnp08028.gho.boulder.ibm.com (b03cxnp08028.gho.boulder.ibm.com [9.17.130.20]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id D7CD71FF0021 for ; Thu, 21 Nov 2013 06:16:39 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp08028.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id rALBFBSk7667918 for ; Thu, 21 Nov 2013 12:15:11 +0100 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id rALDJobV020366 for ; Thu, 21 Nov 2013 06:19:52 -0700 Date: Thu, 21 Nov 2013 05:16:54 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections Message-ID: <20131121131654.GP4138@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20131120153123.GF4138@linux.vnet.ibm.com> <20131120154643.GG19352@mudshark.cambridge.arm.com> <20131120171400.GI4138@linux.vnet.ibm.com> <1384973026.11046.465.camel@schen9-DESK> <20131120190616.GL4138@linux.vnet.ibm.com> <1384979767.11046.489.camel@schen9-DESK> <20131120214402.GM4138@linux.vnet.ibm.com> <1384991514.11046.504.camel@schen9-DESK> <20131121045333.GO4138@linux.vnet.ibm.com> <20131121101736.GA13067@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131121101736.GA13067@mudshark.cambridge.arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Will Deacon Cc: Tim Chen , Ingo Molnar , Andrew Morton , Thomas Gleixner , "linux-kernel@vger.kernel.org" , linux-mm , "linux-arch@vger.kernel.org" , Linus Torvalds , Waiman Long , Andrea Arcangeli , Alex Shi , Andi Kleen , Michel Lespinasse , Davidlohr Bueso , Matthew R Wilcox , Dave Hansen , Peter Zijlstra , Rik van Riel , Peter Hurley , Raghavendra K T , George Spelvin , "H. Peter Anvin" , Arnd Bergmann , Aswin Chandramouleeswaran , Scott J Norton , "Figo.zhang" On Thu, Nov 21, 2013 at 10:17:36AM +0000, Will Deacon wrote: > On Thu, Nov 21, 2013 at 04:53:33AM +0000, Paul E. McKenney wrote: > > On Wed, Nov 20, 2013 at 03:51:54PM -0800, Tim Chen wrote: > > > If we intend to use smp_load_acquire and smp_store_release extensively > > > for locks, making RCsc semantics the default will simply things a lot. > > > > The other option is to weaken lock semantics so that unlock-lock no > > longer implies a full barrier, but I believe that we would regret taking > > that path. (It would be OK by me, I would just add a few smp_mb() > > calls on various slowpaths in RCU. But...) > > Unsurprisingly, my vote is for RCsc semantics. That was in fact my guess. ;-) > One major advantage (in my opinion) of the acquire/release accessors is that > they feel intuitive in an area where intuition is hardly rife. I believe > that the additional reordering permitted by RCpc detracts from the relative > simplicity of what is currently being proposed. Fair point! Let's see what others (both hackers and architectures) say. Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org