linux-kernel - Re: [PATCH 4/7] sched/deadline: reschedule if stop task slip in after pull operations

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Message-ID: <553608B5.8030404@arm.com>
Date:	Tue, 21 Apr 2015 09:22:13 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] sched/deadline: reschedule if stop task slip in after
 pull operations

On 21/04/15 00:02, Wanpeng Li wrote:
> On Tue, Apr 21, 2015 at 06:59:02AM +0800, Wanpeng Li wrote:
>> Hi Juri,
>> On Mon, Apr 20, 2015 at 11:27:22AM +0100, Juri Lelli wrote:
>>> Hi,
>>>
>>> On 06/04/2015 09:53, Wanpeng Li wrote:
>>>> pull_dl_task can drop (and re-acquire) rq->lock, this means a stop task 
>>>> can slip in, in which case we need to reschedule. This patch add the 
>>>> reschedule when the scenario occurs.
>>>>
>>>
>>> Ok, I guess it can happen. Doesn't RT have the same problem? It seems that
>>> it also has to deal with DL tasks slipping in, right?
>>
>> Yeah, I will send another patch to handle RT class in the v2 patchset. :)
> 
> Oh, I just find I have already done them in patch 7/7.
>

Oh, right! That one ended up in another bucket. Sorry about that.

Best,

- Juri

> Regards,
> Wanpeng Li 
> 
>>
>> Regards,
>> Wanpeng Li 
>>
>>>
>>> Thanks,
>>>
>>> - Juri
>>>
>>>> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
>>>> ---
>>>>  kernel/sched/deadline.c | 16 +++++++++++++++-
>>>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>>>> index b8b9355..844da0f 100644
>>>> --- a/kernel/sched/deadline.c
>>>> +++ b/kernel/sched/deadline.c
>>>> @@ -1739,7 +1739,13 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
>>>>  	if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
>>>>  		return;
>>>>  
>>>> -	if (pull_dl_task(rq))
>>>> +	/*
>>>> +	 * pull_dl_task() can drop (and re-acquire) rq->lock; this
>>>> +	 * means a stop task can slip in, in which case we need to
>>>> +	 * reschedule.
>>>> +	 */
>>>> +	if (pull_dl_task(rq) ||
>>>> +		(rq->stop && task_on_rq_queued(rq->stop)))
>>>>  		resched_curr(rq);
>>>>  }
>>>>  
>>>> @@ -1786,6 +1792,14 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
>>>>  			pull_dl_task(rq);
>>>>  
>>>>  		/*
>>>> +		 * pull_dl_task() can drop (and re-acquire) rq->lock; this
>>>> +		 * means a stop task can slip in, in which case we need to
>>>> +		 * reschedule.
>>>> +		 */
>>>> +		if (rq->stop && task_on_rq_queued(rq->stop))
>>>> +			resched_curr(rq);
>>>> +
>>>> +		/*
>>>>  		 * If we now have a earlier deadline task than p,
>>>>  		 * then reschedule, provided p is still on this
>>>>  		 * runqueue.
>>>>
> 

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