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 <rost...@goodmis.org>
> Suggested-by: Peter Zijlstra <pet...@infradead.org>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Li Zhong <zh...@linux.vnet.ibm.com>
> Cc: Don Zickus <dzic...@redhat.com>
> ---
> 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
>
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