linux-kernel - Re: [PATCH 1/4] watchdog: fix rounding issues in get_sample

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Date:	Wed, 18 May 2011 09:53:02 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/4] watchdog: fix rounding issues in get_sample_period()

On Mon, May 16, 2011 at 04:34:58PM -0700, Mandeep Singh Baines wrote:
> In get_sample_period(), softlockup_thresh is integer divided by 5 before
> the multiplication by NSEC_PER_SEC. This results in softlockup_thresh
> being rounded down to the nearest integer multiple of 5.
> 
> For example, a softlockup_thresh of 4 rounds down to 0.

Mandeep,

Thanks for the patches.  Unfortunately, I am taking some time off so I'll
shephard these patches when I get back.  For the most part they look fine,
aside from Ingo's comments.

Cheers,
Don

> 
> Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
> Cc: Marcin Slusarz <marcin.slusarz@...il.com>
> Cc: Don Zickus <dzickus@...hat.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
>  kernel/watchdog.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 14733d4..a06972d 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -110,7 +110,7 @@ static unsigned long get_sample_period(void)
>  	 * increment before the hardlockup detector generates
>  	 * a warning
>  	 */
> -	return softlockup_thresh / 5 * NSEC_PER_SEC;
> +	return softlockup_thresh * (NSEC_PER_SEC / 5);
>  }
>  
>  /* Commands for resetting the watchdog */
> -- 
> 1.7.3.1
> 
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