linux-kernel - Re: [tip:sched/urgent] Sched: fix skip_clock

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Message-ID: <AANLkTi=z3kQJfRqpA5iw91CWyGKnuAC1+qWdao_mS5+4@mail.gmail.com>
Date:	Fri, 10 Dec 2010 10:33:31 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, bbb.lst@...il.com, tglx@...utronix.de,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/urgent] Sched: fix skip_clock_update optimization

On Thu, Dec 9, 2010 at 11:32 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 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.
>

I don't see it on my side.
Then just show some info(don't know if it's helpful):
wake_up_idle_cpu() can set TIF_RESCHED locklessly.

So does
WARN_ON_ONCE(next != rq->idle && test_tsk_need_resched(next));
help?

Thanks,
Yong


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