From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756301Ab3LECgN (ORCPT ); Wed, 4 Dec 2013 21:36:13 -0500 Received: from smtprelay0251.hostedemail.com ([216.40.44.251]:54957 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752401Ab3LECgK (ORCPT ); Wed, 4 Dec 2013 21:36:10 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::,RULES_HIT:41:355:379:541:599:988:989:1260:1261:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1540:1593:1594:1711:1714:1730:1747:1777:1792:2393:2559:2562:2828:3138:3139:3140:3141:3142:3351:3622:3653:3865:3866:3871:3872:4321:4605:5007:7652:7904:8957:10004:10400:10848:11026:11232:11473:11658:11914:12043:12296:12517:12519:12740:13069:13311:13357,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: scent92_8ccba6daf960a X-Filterd-Recvd-Size: 1966 Message-ID: <1386210965.30493.84.camel@joe-AO722> Subject: Re: lots of brief rcu stalls. From: Joe Perches To: Eric Dumazet Cc: paulmck@linux.vnet.ibm.com, Dave Jones , Linux Kernel , Josh Triplett , Ingo Molnar , Peter Zijlstra Date: Wed, 04 Dec 2013 18:36:05 -0800 In-Reply-To: <1386209910.30495.146.camel@edumazet-glaptop2.roam.corp.google.com> References: <20131204232838.GA25592@redhat.com> <20131205001614.GI15492@linux.vnet.ibm.com> <1386209910.30495.146.camel@edumazet-glaptop2.roam.corp.google.com> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.8.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-12-04 at 18:18 -0800, Eric Dumazet wrote: > On Wed, 2013-12-04 at 16:16 -0800, Paul E. McKenney wrote: > > + ULONG_CMP_GE(ACCESS_ONCE(jiffies), rdp->rsp->jiffies_resched)) { perhaps time_before_eq > jiffies should not need ACCESS_ONCE(), right ? > > It is one of the few variables marked with volatile keyword. It does seem redundant $ git grep -n "ACCESS_ONCE(jiffies)" kernel/rcu/torture.c:1354: jiffies_snap = ACCESS_ONCE(jiffies); kernel/rcu/torture.c:1363: jiffies_snap = ACCESS_ONCE(jiffies); kernel/rcu/tree.c:820: unsigned long j = ACCESS_ONCE(jiffies); kernel/rcu/tree.c:975: j = ACCESS_ONCE(jiffies); kernel/sched/core.c:2324: unsigned long next, now = ACCESS_ONCE(jiffies); kernel/sched/proc.c:536: unsigned long curr_jiffies = ACCESS_ONCE(jiffies); kernel/sched/proc.c:558: unsigned long curr_jiffies = ACCESS_ONCE(jiffies);