From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751670AbdGYSMa (ORCPT ); Tue, 25 Jul 2017 14:12:30 -0400 Received: from smtprelay0028.hostedemail.com ([216.40.44.28]:58449 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751210AbdGYSM3 (ORCPT ); Tue, 25 Jul 2017 14:12:29 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2198:2199:2393:2553:2559:2562:2693:2731:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3874:4321:5007:6119:6261:6742:7875:8957:9010:9389:10004:10400:10848:10967:11232:11658:11914:12740:12760:12895:13069:13255:13311:13357:13439:14040:14096:14097:14181:14659:14721:21080:21433:21627:30012:30054:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: door51_321db4bc6733c X-Filterd-Recvd-Size: 2473 Date: Tue, 25 Jul 2017 14:12:20 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH tip/core/rcu 02/15] rcu: Use timer as backstop for NOCB deferred wakeups Message-ID: <20170725141220.4d2d968e@vmware.local.home> In-Reply-To: <1500932684-10469-2-git-send-email-paulmck@linux.vnet.ibm.com> References: <20170724214425.GA9665@linux.vnet.ibm.com> <1500932684-10469-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.15.0-dirty (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 24 Jul 2017 14:44:31 -0700 "Paul E. McKenney" wrote: > The handling of RCU's no-CBs CPUs has a maintenance headache, namely > that if call_rcu() is invoked with interrupts disabled, the rcuo kthread > wakeup must be defered to a point where we can be sure that scheduler > locks are not held. Of course, there are a lot of code paths leading > from an interrupts-disabled invocation of call_rcu(), and missing any > one of these can result in excessive callback-invocation latency, and > potentially even system hangs. What about using irq_work? That's what perf and ftrace use for such a case. -- Steve > > This commit therefore uses a timer to guarantee that the wakeup will > eventually occur. If one of the deferred-wakeup points kicks in, then > the timer is simply cancelled. > > This commit also fixes up an incomplete removal of commits that were > intended to plug remaining exit paths, which should have the added > benefit of reducing the overhead of RCU's context-switch hooks. In > addition, it simplifies leader-to-follower callback-list handoff by > introducing locking. The call_rcu()-to-leader handoff continues to > use atomic operations in order to maintain good real-time latency for > common-case use of call_rcu(). >