linux-kernel - Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq

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Date:	Tue, 4 Nov 2014 22:19:33 +0800
From:	"pang.xunlei" <pang.xunlei@...aro.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq_dl() for non-DL
 curr task

On 4 November 2014 19:24, Wanpeng Li <kernellwp@...il.com> wrote:
>
> On 14/11/4 下午7:13, pang.xunlei wrote:
>>
>> When selecting the cpu for a waking DL task, if curr is a non-DL
>> task which is bound only on this cpu, then we can give it a chance
>> to select a different cpu for this DL task to avoid curr starving.
>>
>> Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
>> ---
>>   kernel/sched/deadline.c |   14 ++++++++++----
>>   1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 7b0b2d2..1f64d4a 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -954,6 +954,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int
>> sd_flag, int flags)
>>         struct task_struct *curr;
>>         struct rq *rq;
>>   +     if (p->nr_cpus_allowed == 1)
>> +               goto out;
>> +
>>         if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
>>                 goto out;
>
>
> I don't think you use right branch of tip tree.
Hi Wanpeng, I'm using linux-3.18-rc3 as the base, does this have
something wrong? please point me out if any.
Thanks!
>
> Regards,
> Wanpeng Li
>
>>   @@ -970,11 +973,14 @@ select_task_rq_dl(struct task_struct *p, int cpu,
>> int sd_flag, int flags)
>>          * can!) we prefer to send it somewhere else. On the
>>          * other hand, if it has a shorter deadline, we
>>          * try to make it stay here, it might be important.
>> +        *
>> +        * If the current task on @p's runqueue is a non-DL task,
>> +        * and this task is bound on current runqueue, then try to
>> +        * see if we can wake this DL task up on a different runqueue,
>>          */
>> -       if (unlikely(dl_task(curr)) &&
>> -           (curr->nr_cpus_allowed < 2 ||
>> -            !dl_entity_preempt(&p->dl, &curr->dl)) &&
>> -           (p->nr_cpus_allowed > 1)) {
>> +       if (unlikely(curr->nr_cpus_allowed < 2) ||
>> +               unlikely(dl_task(curr) &&
>> +                               !dl_entity_preempt(&p->dl, &curr->dl))) {
>>                 int target = find_later_rq(p);
>>                 if (target != -1)
>
>
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