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

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Date:	Fri, 27 Jun 2008 14:43:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Johannes Weiner <hannes@...urebad.de>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 3/3] softlockup: fix watchdog task wakeup frequency


* Johannes Weiner <hannes@...urebad.de> wrote:

> Hm, it updates the timestamp, so it makes only sense if it runs at a 
> maximum every second (timestamp granularity) or even less.  The check 
> for hung tasks uses the cpu timestamp as well for comparison, so that 
> would be okay too.
> 
> Like this?
> 
> diff --git a/kernel/softlockup.c b/kernel/softlockup.c
> index c828c23..b884546 100644
> --- a/kernel/softlockup.c
> +++ b/kernel/softlockup.c
> @@ -106,8 +106,9 @@ 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));

yeah - but please use the best possible coding style. Two-line comments 
should be in the:

  /*
   * Here we ......................
   * ........................ come:
   */

... format. And the arithmetics should be:

	if (now > touch_timestamp + softlockup_thresh/2)

(the unnecessary paranthesis was a small style mistake in the original 
too)

	Ingo
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