linux-kernel - Re: [PATCH 2/2] sched: Fix "divide error: 0000" in find_busiest

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Date:	Tue, 19 Jul 2011 23:18:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Terry Loftin <terry.loftin@...com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Bob Montgomery <bob.montgomery@...com>
Subject: Re: [PATCH 2/2] sched: Fix "divide error: 0000" in
 find_busiest_group

On Tue, 2011-07-19 at 14:58 -0600, Terry Loftin wrote:
> Add a check to sched_avg_update() to detect and reset age_stamp if the
> clock value has wrapped.  Because __cycles_2_ns() includes an offset
> to account for start up time, the clock may not wrap to zero, so use
> the current clock value instead.

So you're running on a platform (unspecified) where we use a raw
sched_clock() that is buggy. Again, you're fixing symptoms not causes. 

> Signed-off-by: Terry Loftin <terry.loftin@...com>
> Signed-off-by: Bob Montgomery <bob.montgomery@...com>
> ---
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 18d38e4..b39cae1 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1256,6 +1256,8 @@ static void sched_avg_update(struct rq *rq)
>  {
>  	s64 period = sched_avg_period();
> 
> +	if (unlikely(rq->age_stamp > rq->clock))
> +		rq->age_stamp = rq->clock;
>  	while ((s64)(rq->clock - rq->age_stamp) > period) {
>  		/*
>  		 * Inline assembly required to prevent the compiler



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