linux-kernel - Re: [RFC PATCH v3] sched/deadline: support dl task migration during cpu hotplug

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Date:	Tue, 11 Nov 2014 19:55:19 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@....com>,
	Kirill Tkhai <ktkhai@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3] sched/deadline: support dl task migration during
 cpu hotplug

Hi Peter,
On 14/11/11 下午7:33, Peter Zijlstra wrote:
> On Thu, Nov 06, 2014 at 10:40:49AM +0800, Wanpeng Li wrote:
>> @@ -538,6 +539,46 @@ again:
>>   	update_rq_clock(rq);
>>   	dl_se->dl_throttled = 0;
>>   	dl_se->dl_yielded = 0;
>> +
>> +	/*
>> +	 * So if we find that the rq the task was on is no longer
>> +	 * available, we need to select a new rq.
>> +	 */
>> +	if (!rq->online) {
>> +		struct rq *later_rq = NULL;
>> +
>> +		raw_spin_unlock(&rq->lock);
>> +
>> +		later_rq = find_lock_later_rq(p, rq);
>> +
>> +		if (!later_rq) {
>> +			int cpu;
>> +
>> +			/*
>> +			 * If cannot preempt any rq, fallback to pick any
>> +			 * online cpu.
>> +			 */
>> +			for_each_cpu(cpu, &p->cpus_allowed)
>> +				if (cpu_online(cpu))
>> +					later_rq = cpu_rq(cpu);
> 			cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p));
> 			if (cpu >= nr_cpu_ids)
> 				/* fail */
>
> 			later_rq = cpu_rq(cpu);

Ok.

>> +			if (!later_rq) {
>> +				pr_warn("fail to find any online and task
>> +						will never come back to us\n");
>> +				goto out;
>> +			}
>> +		}
>> +
>> +		deactivate_task(rq, p, 0);
>> +		set_task_cpu(p, later_rq->cpu);
>> +		activate_task(later_rq, p, 0);
>> +
>> +		resched_curr(later_rq);
>> +
>> +		double_unlock_balance(rq, later_rq);
>> +
>> +		goto out;
>> +	}
>> +
>>   	if (task_on_rq_queued(p)) {
>>   		enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
>>   		if (dl_task(rq->curr))
>> @@ -555,7 +596,7 @@ again:
>>   	}
>>   unlock:
>>   	raw_spin_unlock(&rq->lock);
>> -
>> +out:
>>   	return HRTIMER_NORESTART;
>>   }
>>   
>> @@ -1185,8 +1226,12 @@ 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);
>> +	if (likely(task_rq(task)->online)) {
>> +		cpumask_copy(later_mask, task_rq(task)->rd->span);
>> +		cpumask_and(later_mask, later_mask, cpu_active_mask);
>> +	} else
>> +		/* for offline cpus we have a singleton rd */
>> +		cpumask_copy(later_mask, cpu_active_mask);
>>   	cpumask_and(later_mask, later_mask, &task->cpus_allowed);
>>   	best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
>>   			task, later_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);
>
> Is the same, right and less lines.

Thanks for your great help! I will fold these to my patch and send out a 
newer version tomorrow. ;-)

Regards,
Wanpeng Li

>
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