Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757578Ab3ETRxR (ORCPT ); Mon, 20 May 2013 13:53:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59945 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753342Ab3ETRxQ (ORCPT ); Mon, 20 May 2013 13:53:16 -0400 Date: Mon, 20 May 2013 13:52:29 -0400 From: Don Zickus To: Frederic Weisbecker Cc: LKML , Steven Rostedt , "Paul E. McKenney" , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Li Zhong Subject: Re: [PATCH 3/8] watchdog: Boot-disable by default on full dynticks Message-ID: <20130520175229.GI133453@redhat.com> References: <1369065716-22801-1-git-send-email-fweisbec@gmail.com> <1369065716-22801-4-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1369065716-22801-4-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: 2195 Lines: 61 On Mon, May 20, 2013 at 06:01:51PM +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 Peter committed a patch to perf so that this isn't needed any more? 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 > --- > kernel/watchdog.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 05039e3..7e1a021 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -543,6 +543,12 @@ static struct smp_hotplug_thread watchdog_threads = { > > void __init lockup_detector_init(void) > { > +#ifdef CONFIG_NO_HZ_FULL > + watchdog_enabled = 0; > + watchdog_disabled = 1; > + pr_warning("Disabled lockup detectors by default because of full dynticks\n"); > + pr_warning("You can overwrite that with 'sysctl -w kernel.watchdog=1'\n"); > +#endif > set_sample_period(); > if (smpboot_register_percpu_thread(&watchdog_threads)) { > pr_err("Failed to create watchdog threads, disabled\n"); > -- > 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/