On Wed, Jun 12, 2013 at 04:02:36PM +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 we had a conversation awhile ago, where we agreed this was going
to be fixed for 3.11? Didn't Peter find the patch and apply it to his
tree? I am confused why this is still needed?
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>
> Cc: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
> Cc: Anish Singh <anish198519851...@gmail.com>
> ---
> kernel/watchdog.c | 8 ++++++++
> 1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 52c9a9b..277d713 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -553,6 +553,14 @@ void __init lockup_detector_init(void)
> {
> set_sample_period();
>
> +#ifdef CONFIG_NO_HZ_FULL
> + if (watchdog_enabled) {
> + watchdog_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_enabled)
> watchdog_enable_all_cpus();
> }
> --
> 1.7.5.4
>
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