Commit 940be35a authored Jun 07, 2013 by Frederic Weisbecker

watchdog: Boot-disable by default on full dynticks



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 <rostedt@goodmis.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Anish Singh <anish198519851985@gmail.com>

parent 3c00ea82

kernel/watchdog.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -553,6 +553,14 @@ void __init lockup_detector_init(void)
		{
		set_sample_period();

		#ifdef CONFIG_NO_HZ_FULL
		if (watchdog_user_enabled) {
		watchdog_user_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_user_enabled)
		watchdog_enable_all_cpus();
		}

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