From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757490Ab3ETQCP (ORCPT ); Mon, 20 May 2013 12:02:15 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:64197 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756903Ab3ETQCJ (ORCPT ); Mon, 20 May 2013 12:02:09 -0400 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Steven Rostedt , "Paul E. McKenney" , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Li Zhong , Don Zickus Subject: [PATCH 3/8] watchdog: Boot-disable by default on full dynticks Date: Mon, 20 May 2013 18:01:51 +0200 Message-Id: <1369065716-22801-4-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1369065716-22801-1-git-send-email-fweisbec@gmail.com> References: <1369065716-22801-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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