From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f172.google.com (mail-ob0-f172.google.com [209.85.214.172]) by kanga.kvack.org (Postfix) with ESMTP id 149DF6B0036 for ; Thu, 21 Nov 2013 08:18:15 -0500 (EST) Received: by mail-ob0-f172.google.com with SMTP id gq1so6721645obb.17 for ; Thu, 21 Nov 2013 05:18:14 -0800 (PST) Received: from e31.co.us.ibm.com (e31.co.us.ibm.com. [32.97.110.149]) by mx.google.com with ESMTPS id n6si19383728oeq.134.2013.11.21.05.18.13 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 21 Nov 2013 05:18:14 -0800 (PST) Received: from /spool/local by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 21 Nov 2013 06:18:13 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id 88F1D3E40040 for ; Thu, 21 Nov 2013 06:18:10 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp08027.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id rALBGNnH27983922 for ; Thu, 21 Nov 2013 12:16:23 +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 rALDL3xd024706 for ; Thu, 21 Nov 2013 06:21:04 -0700 Date: Thu, 21 Nov 2013 05:18:06 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections Message-ID: <20131121131806.GQ4138@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> <20131121104503.GB10022@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131121104503.GB10022@twins.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Tim Chen , Will Deacon , 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 , 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 11:45:03AM +0100, Peter Zijlstra wrote: > On Wed, Nov 20, 2013 at 08:53:33PM -0800, Paul E. McKenney wrote: > > 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...) > > Please no, I know we rely on it in a number of places, I just can't > remember where all those were :/ ;-) ;-) ;-) Yeah, I would also have to overprovision smp_mb()s in a number of places. Then again, I know that I don't rely on this on any of RCU's fastpaths. 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