Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757293Ab3FLREX (ORCPT ); Wed, 12 Jun 2013 13:04:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32771 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755695Ab3FLREW (ORCPT ); Wed, 12 Jun 2013 13:04:22 -0400 Date: Wed, 12 Jun 2013 13:03:16 -0400 From: Don Zickus To: Frederic Weisbecker Cc: LKML , Steven Rostedt , "Paul E. McKenney" , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Li Zhong , "Srivatsa S. Bhat" , Anish Singh Subject: Re: [PATCH 4/6] watchdog: Boot-disable by default on full dynticks Message-ID: <20130612170316.GO133453@redhat.com> References: <1371045758-5296-1-git-send-email-fweisbec@gmail.com> <1371045758-5296-5-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1371045758-5296-5-git-send-email-fweisbec@gmail.com> 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: 2308 Lines: 66 On Wed, Jun 12, 2013 at 04:02:36PM +0200, Frederic Weisbecker wrote: > When the watchdog runs, it prevents the full dynticks > CPUs from stopping their tick because the hard lockup > detector uses perf events internally, which in turn > rely on the periodic tick. > > Since this is a rather confusing behaviour that is not > easy to track down and identify for those who want to > test CONFIG_NO_HZ_FULL, let's default disable the > watchdog on boot time when full dynticks is enabled. > > The user can still enable it later on runtime using > proc or sysctl. I thought we had a conversation awhile ago, where we agreed this was going to be fixed for 3.11? Didn't Peter find the patch and apply it to his tree? I am confused why this is still needed? Cheers, Don > > Reported-by: Steven Rostedt > Suggested-by: Peter Zijlstra > Signed-off-by: Frederic Weisbecker > Cc: Steven Rostedt > Cc: Paul E. McKenney > Cc: Ingo Molnar > Cc: Andrew Morton > Cc: Thomas Gleixner > Cc: Peter Zijlstra > Cc: Li Zhong > Cc: Don Zickus > Cc: Srivatsa S. Bhat > Cc: Anish Singh > --- > kernel/watchdog.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 52c9a9b..277d713 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -553,6 +553,14 @@ void __init lockup_detector_init(void) > { > set_sample_period(); > > +#ifdef CONFIG_NO_HZ_FULL > + if (watchdog_enabled) { > + watchdog_enabled = 0; > + pr_warning("Disabled lockup detectors by default for full dynticks\n"); > + pr_warning("You can reactivate it with 'sysctl -w kernel.watchdog=1'\n"); > + } > +#endif > + > if (watchdog_enabled) > watchdog_enable_all_cpus(); > } > -- > 1.7.5.4 > -- 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/