linux-kernel - Re: [PATCH 3/3] softlockup: fix watchdog task wakeup frequency

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Date:	Sat, 28 Jun 2008 02:45:42 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 3/3] softlockup: fix watchdog task wakeup frequency

Hi,

Johannes Weiner <hannes@...urebad.de> writes:

> From: Johannes Weiner <hannes@...urebad.de>
> Subject: [PATCH 3/3] softlockup: wake up watchdog twice per threshold timespan
>
> Updating the timestamp more often is pointless as we print the warnings
> only if we exceed the threshold.  And the check for hung tasks relies on
> the last timestamp, so it will keep working correctly, too.
>
> Signed-off-by: Johannes Weiner <hannes@...urebad.de>
> ---
>  kernel/softlockup.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> --- a/kernel/softlockup.c
> +++ b/kernel/softlockup.c
> @@ -107,8 +107,11 @@ void softlockup_tick(void)
>  
>  	now = get_timestamp(this_cpu);
>  
> -	/* Wake up the high-prio watchdog task every second: */
> -	if (now > (touch_timestamp + 1))
> +	/*
> +	 * Wake up the high-prio watchdog task twice per
> +	 * threshold timespan.
> +	 */
> +	if (now > touch_timestamp + softlockup_thresh/2)
>  		wake_up_process(per_cpu(watchdog_task, this_cpu));

That defeats patch 1/3 and I think it can be dropped (#1).

	Hannes
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