From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qa0-f48.google.com (mail-qa0-f48.google.com [209.85.216.48]) by kanga.kvack.org (Postfix) with ESMTP id 536AF6B0035 for ; Sat, 30 Nov 2013 12:38:54 -0500 (EST) Received: by mail-qa0-f48.google.com with SMTP id w5so2883512qac.7 for ; Sat, 30 Nov 2013 09:38:54 -0800 (PST) Received: from e35.co.us.ibm.com (e35.co.us.ibm.com. [32.97.110.153]) by mx.google.com with ESMTPS id a4si11086786qar.172.2013.11.30.09.38.52 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Sat, 30 Nov 2013 09:38:53 -0800 (PST) Received: from /spool/local by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 30 Nov 2013 10:38:52 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id B18241FF0021 for ; Sat, 30 Nov 2013 10:38:29 -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 rAUFaxR341746476 for ; Sat, 30 Nov 2013 16:36:59 +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 rAUHfkmN007016 for ; Sat, 30 Nov 2013 10:41:48 -0700 Date: Sat, 30 Nov 2013 09:38:43 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections Message-ID: <20131130173843.GZ4137@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20131127101613.GC9032@mudshark.cambridge.arm.com> <20131127171143.GN4137@linux.vnet.ibm.com> <20131128114058.GC21354@mudshark.cambridge.arm.com> <20131128173853.GV4137@linux.vnet.ibm.com> <20131128180318.GE16203@mudshark.cambridge.arm.com> <20131128182712.GW4137@linux.vnet.ibm.com> <20131128185341.GG16203@mudshark.cambridge.arm.com> <20131128195039.GX4137@linux.vnet.ibm.com> <20131129161711.GG31000@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Will Deacon , Arnd Bergmann , "Figo. zhang" , Aswin Chandramouleeswaran , Rik van Riel , Waiman Long , "linux-kernel@vger.kernel.org" , Raghavendra K T , "linux-arch@vger.kernel.org" , Andi Kleen , George Spelvin , Tim Chen , Michel Lespinasse , Ingo Molnar , Peter Hurley , "H. Peter Anvin" , Andrew Morton , linux-mm , Alex Shi , Andrea Arcangeli , Scott J Norton , Thomas Gleixner , Dave Hansen , Peter Zijlstra , Matthew R Wilcox , Davidlohr Bueso On Fri, Nov 29, 2013 at 08:44:41AM -0800, Linus Torvalds wrote: > On Nov 29, 2013 8:18 AM, "Will Deacon" wrote: > > > > To get some sort of > > idea, I tried adding a dmb to the start of spin_unlock on ARMv7 and I saw > a > > 3% performance hit in hackbench on my dual-cluster board. > > Don't do a dmb. Just do a dummy release. You just said that on arm64 a > unlock+lock is a memory barrier, so just make the mb__before_spinlock() be > a dummy store with release to the stack.. > > That should be noticeably cheaper than a full dmb. Cute! I like it! ;-) 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