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

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Date:	Mon, 17 Nov 2014 06:59:14 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org
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. 

Regards,
Wanpeng Li 

>> >
>> > Kirill
>> >
>> >
>> > --
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