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Subject: Re: [tip:sched/urgent] Sched: fix skip_clock_update optimization
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
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        yong.zhang0@gmail.com, mingo@elte.hu
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References: <1291802742.1417.9.camel@marge.simson.net>
	 <tip-f26f9aff6aaf67e9a430d16c266f91b13a5bff64@git.kernel.org>
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Date: Thu, 09 Dec 2010 16:32:53 +0100
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On Wed, 2010-12-08 at 20:40 +0000, tip-bot for Mike Galbraith wrote:
> @@ -4063,6 +4062,8 @@ need_resched_nonpreemptible:
>  
>         put_prev_task(rq, prev);
>         next = pick_next_task(rq);
> +       clear_tsk_need_resched(prev);
> +       rq->skip_clock_update = 0;
>  
>         if (likely(prev != next)) {
>                 sched_info_switch(prev, next);
> @@ -4071,6 +4072,7 @@ need_resched_nonpreemptible:
>                 rq->nr_switches++;
>                 rq->curr = next;
>                 ++*switch_count;
> +               WARN_ON_ONCE(test_tsk_need_resched(next)); 

I just managed to trigger this one.. will try and reproduce to find out
wth happened.