From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751594Ab3ESQSv (ORCPT ); Sun, 19 May 2013 12:18:51 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:38241 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751102Ab3ESQSt (ORCPT ); Sun, 19 May 2013 12:18:49 -0400 Date: Sun, 19 May 2013 09:18:43 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Peter Zijlstra , Don Zickus , Frederic Weisbecker , Ingo Molnar , LKML , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" Subject: Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled Message-ID: <20130519161843.GI4006@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1368547372-21011-2-git-send-email-fweisbec@gmail.com> <20130515083729.GC10510@laptop.programming.kicks-ass.net> <20130515150652.GP23604@redhat.com> <1368631622.6828.69.camel@gandalf.local.home> <20130515165915.GE13916@laptop.home> <1368637441.6828.70.camel@gandalf.local.home> <20130516081027.GD19669@dyad.programming.kicks-ass.net> <20130516150706.GY4442@linux.vnet.ibm.com> <20130516175602.GL19669@dyad.programming.kicks-ass.net> <1368729178.6828.105.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368729178.6828.105.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13051916-3620-0000-0000-000002919952 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 16, 2013 at 02:32:58PM -0400, Steven Rostedt wrote: > On Thu, 2013-05-16 at 19:56 +0200, Peter Zijlstra wrote: > > > I suppose the fundamental question was: will receiving NMIs negate NO_HZ_FULL's > > functionality? That is, will the getting of NMIs make us drop out of NO_HZ_FULL > > and re-enable all sorts of things? > > It shouldn't. The nmi_enter() notifies RCU that it can no longer ignore > this CPU, where as nmi_enter() tells it that it can ignore it, as it has > re-entered user space. > > > > > Because clearly RCU needs to exit from EQS, which might (or might not) mean > > leaving NO_HZ_FULL. > > Yep, but the two are pretty much agnostic from each other. > > We only need to leave NO_HZ_FULL if RCU (or anything for that matter) > required having a tick again. But as Paul said, getting an NMI in idle > wont restart the tick, so there's no need to restart it here either. > > Now if an NMI were to do a call_rcu() then it would require a tick. But > NMIs doing call_rcu() has much bigger issues to worry about ;-) Someone invoking call_rcu() from an NMI handler will get what they deserve, good and hard! ;-) Thanx, Paul > -- Steve > > > > > I'm not entirely up-to-date on those details. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >