linux-kernel - Re:[PATCH v5] sched/deadline: support dl task migration during cpu hotplug

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Message-Id: <391401416243011@web3h.yandex.ru>
Date:	Mon, 17 Nov 2014 19:50:11 +0300
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
	Kirill Tkhai <ktkhai@...allels.com>
Subject: Re:[PATCH v5] sched/deadline: support dl task migration during cpu hotplug



> Hi Kirill,
> On Thu, Nov 13, 2014 at 01:21:31PM +0300, Kirill Tkhai wrote:
> 
>>>>>>> @@ -1185,8 +1223,9 @@ static int find_later_rq(struct task_struct *task)
>>>>>>> * We have to consider system topology and task affinity
>>>>>>> * first, then we can look for a suitable cpu.
>>>>>>> */
>>>>>>> - cpumask_copy(later_mask, task_rq(task)->rd->span);
>>>>>>> - cpumask_and(later_mask, later_mask, cpu_active_mask);
>>>>>>> + cpumask_copy(later_mask, cpu_active_mask);
>>>>>>> + if (likely(task_rq(task)->online))
>>>>>>> + cpumask_and(later_mask, later_mask, task_rq(task)->rd->span);
>>>>>>> cpumask_and(later_mask, later_mask, &task->cpus_allowed);
>>>>>>> best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
>>>>>>> task, later_mask);
>>>>
>>>> Also, we should think about the following situation.
>>>>
>>>> DL task is left on dead rq. In your scheme it will be moved by the timer.
>>>> But what will be if somebody changes the class of the task (before timer)?
>>>
>>> I think timer will be cancelled in switched_from_dl().
>>
>> Yeah, but nobody will move this task to alive rq.
>>
>>> Regards,
>>> Wanpeng Li
>>>
>>>> In this case the task still remains on dead rq.
>>>>
>>>> We should handle this situation in some way.
> 
> Your proposal is a great appreciated.

Sadly, I‘m travelling at the moment, I‘m not able to do something till december.

> Regards,
> Wanpeng Li
> 
>>>> Kirill
>>>>
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