From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qe0-f54.google.com (mail-qe0-f54.google.com [209.85.128.54]) by kanga.kvack.org (Postfix) with ESMTP id 387066B00D8 for ; Mon, 25 Nov 2013 12:54:22 -0500 (EST) Received: by mail-qe0-f54.google.com with SMTP id cy11so2553321qeb.13 for ; Mon, 25 Nov 2013 09:54:22 -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 q6si8434878qag.88.2013.11.25.09.54.20 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 25 Nov 2013 09:54:21 -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 ; Mon, 25 Nov 2013 10:54:20 -0700 Received: from b03cxnp07027.gho.boulder.ibm.com (b03cxnp07027.gho.boulder.ibm.com [9.17.130.14]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id C0C6D19D8041 for ; Mon, 25 Nov 2013 10:54:12 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp07027.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id rAPFqHM28257950 for ; Mon, 25 Nov 2013 16:52:17 +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 rAPHvBvS014784 for ; Mon, 25 Nov 2013 10:57:14 -0700 Date: Mon, 25 Nov 2013 09:54:12 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections Message-ID: <20131125175412.GP4138@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20131122203738.GC4138@linux.vnet.ibm.com> <20131122215208.GD4138@linux.vnet.ibm.com> <20131123002542.GF4138@linux.vnet.ibm.com> <20131123013654.GG4138@linux.vnet.ibm.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: Ingo Molnar , Tim Chen , Will Deacon , Ingo Molnar , Andrew Morton , Thomas Gleixner , "linux-kernel@vger.kernel.org" , linux-mm , "linux-arch@vger.kernel.org" , 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 Sat, Nov 23, 2013 at 12:39:53PM -0800, Linus Torvalds wrote: > On Sat, Nov 23, 2013 at 12:21 PM, Linus Torvalds > wrote: > > > > And as far as I can tell, the above gives you: A < B < C < D < E < F < > > A. Which doesn't look possible. > > Hmm.. I guess technically all of those cases aren't "strictly > precedes" as much as "cannot have happened in the opposite order". So > the "<" might be "<=". Which I guess *is* possible: "it all happened > at the same time". And then the difference between your suggested > "lwsync" and "sync" in the unlock path on CPU0 basically approximating > the difference between "A <= B" and "A < B".. > > Ho humm. Indeed, the difference between "<" and "<=" does not matter here. 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