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

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Date:	Tue, 21 Apr 2015 06:59:02 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Juri Lelli <juri.lelli@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH 4/7] sched/deadline: reschedule if stop task slip in
 after pull operations

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. :)

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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