Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932428Ab3EOIht (ORCPT ); Wed, 15 May 2013 04:37:49 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:52412 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757466Ab3EOIhr (ORCPT ); Wed, 15 May 2013 04:37:47 -0400 Date: Wed, 15 May 2013 10:37:29 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Steven Rostedt , "Paul E. McKenney" , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" , dzickus@redhat.com Subject: Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled Message-ID: <20130515083729.GC10510@laptop.programming.kicks-ass.net> References: <1368547372-21011-1-git-send-email-fweisbec@gmail.com> <1368547372-21011-2-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368547372-21011-2-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1378 Lines: 33 On Tue, May 14, 2013 at 06:02:51PM +0200, Frederic Weisbecker wrote: > From: Steven Rostedt > > Trying to test the nohz_full code, I was not able to get it to work. > Finally I enabled the tick_stop tracepoint and it showed: > > tick_stop: success=no msg=perf events running > > I talked to Frederic Weisbecker about this and he informed me that > perf is used by the lockup detector. I checked the code, and sure > enough it is. > > As perf is always running when LOCKUP_DETECTOR is enabled, which > will always disable nohz_full from working, instead of confusing > users, disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled. > > When perf is changed such that it does not prevent nohz_full from > working, then we can and should remove this constraint. That's a bit contradictory in function, you want the NMI watchdog to cover all code, so disabling whilst entering NO_HZ state is going to make it not cover some code - *fail*. Rather I would suggest disabling the NMI watchdog's runtime default; so you can still enable it with something like: echo 1 > /proc/sys/kernel/nmi_watchdog -- 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/