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watchdog: Boot-disable by default on full dynticks

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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 <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Li Zhong <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Srivatsa S. Bhat <[email protected]>
Cc: Anish Singh <[email protected]>
This commit is contained in:
Frederic Weisbecker 2013-06-07 13:35:42 +02:00
commit 940be35ac0
1 changed files with 8 additions and 0 deletions
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8
kernel/watchdog.c
View file

@ -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();
}