Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759169Ab3EOQIv (ORCPT ); Wed, 15 May 2013 12:08:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756602Ab3EOQIu (ORCPT ); Wed, 15 May 2013 12:08:50 -0400 Date: Wed, 15 May 2013 12:26:54 -0400 From: Don Zickus To: Steven Rostedt Cc: Peter Zijlstra , Frederic Weisbecker , Ingo Molnar , LKML , "Paul E. McKenney" , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" Subject: Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled Message-ID: <20130515162654.GR23604@redhat.com> References: <1368547372-21011-1-git-send-email-fweisbec@gmail.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368631622.6828.69.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1057 Lines: 22 On Wed, May 15, 2013 at 11:27:02AM -0400, Steven Rostedt wrote: > > Coming into the middle of the thread is always hard, but why/how does perf > > disable nohz_full? I didn't think the hardware events of perf would cause > > problems as they are no different than an irq. Curious. > > Right now perf requires a tick, not sure exactly why, but you can look > at the code in perf_event_task_tick(). Thus if NO_HZ_FULL sees that a > perf tick is pending, it won't disable ticks. Unfortunately, the > watchdogs, both NMI and soft lockup, use the perf infrastructure to > trigger NMIs or interrupts. This adds a perf element on the rotate list > and keeps NO_HZ_FULL from *ever* activating. Ok. Thanks. I don't know what the rotate list is for (nor what it does in general). But I'll poke around. Cheers, Don -- 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/