From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by kanga.kvack.org (Postfix) with ESMTP id E2E266B0039 for ; Tue, 19 Nov 2013 18:05:51 -0500 (EST) Received: by mail-pa0-f51.google.com with SMTP id fa1so150752pad.38 for ; Tue, 19 Nov 2013 15:05:51 -0800 (PST) Received: from psmtp.com ([74.125.245.188]) by mx.google.com with SMTP id yk3si12635505pac.302.2013.11.19.15.05.49 for ; Tue, 19 Nov 2013 15:05:50 -0800 (PST) Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 19 Nov 2013 16:05:48 -0700 Received: from b03cxnp07028.gho.boulder.ibm.com (b03cxnp07028.gho.boulder.ibm.com [9.17.130.15]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 9B4F219D8041 for ; Tue, 19 Nov 2013 16:05:40 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp07028.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id rAJL3lU19699728 for ; Tue, 19 Nov 2013 22:03:47 +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 rAJN8bTO026642 for ; Tue, 19 Nov 2013 16:08:39 -0700 Date: Tue, 19 Nov 2013 15:05:42 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v5 2/4] MCS Lock: optimizations and extra comments Message-ID: <20131119230542.GW4138@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1383940325.11046.415.camel@schen9-DESK> <20131119191310.GO4138@linux.vnet.ibm.com> <1384901861.11046.449.camel@schen9-DESK> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1384901861.11046.449.camel@schen9-DESK> Sender: owner-linux-mm@kvack.org List-ID: To: Tim Chen Cc: 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 , Will Deacon , "Figo.zhang" On Tue, Nov 19, 2013 at 02:57:41PM -0800, Tim Chen wrote: > On Tue, 2013-11-19 at 11:13 -0800, Paul E. McKenney wrote: > > On Fri, Nov 08, 2013 at 11:52:05AM -0800, Tim Chen wrote: > > > > > > +/* > > > + * Releases the lock. The caller should pass in the corresponding node that > > > + * was used to acquire the lock. > > > + */ > > > static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) > > > { > > > struct mcs_spinlock *next = ACCESS_ONCE(node->next); > > > @@ -51,7 +60,7 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod > > > /* > > > * Release the lock by setting it to NULL > > > */ > > > - if (cmpxchg(lock, node, NULL) == node) > > > + if (likely(cmpxchg(lock, node, NULL) == node)) > > > > Agreed here as well. Takes a narrow race to hit this. > > > > So, did your testing exercise this path? If the answer is "yes", > > > Paul, > > I did some instrumentation and confirmed that the path in question has > been exercised. So this patch should be okay. Very good! 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