From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id 5EDF76B0036 for ; Tue, 19 Nov 2013 17:59:46 -0500 (EST) Received: by mail-pa0-f47.google.com with SMTP id kq14so4494402pab.34 for ; Tue, 19 Nov 2013 14:59:46 -0800 (PST) Received: from psmtp.com ([74.125.245.184]) by mx.google.com with SMTP id n8si12647576pax.218.2013.11.19.14.59.44 for ; Tue, 19 Nov 2013 14:59:45 -0800 (PST) Subject: Re: [PATCH v5 2/4] MCS Lock: optimizations and extra comments From: Tim Chen In-Reply-To: <20131119191310.GO4138@linux.vnet.ibm.com> References: <1383940325.11046.415.camel@schen9-DESK> <20131119191310.GO4138@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Nov 2013 14:57:41 -0800 Message-ID: <1384901861.11046.449.camel@schen9-DESK> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: paulmck@linux.vnet.ibm.com 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, 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. Tim > and if the issues that I called out in patch #1 are resolved: > > Reviewed-by: Paul E. McKenney > > > return; > > /* Wait until the next pointer is set */ > > while (!(next = ACCESS_ONCE(node->next))) > > -- 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