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

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Date:	Wed, 05 Nov 2014 07:30:40 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	"pang.xunlei" <pang.xunlei@...aro.org>
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

Hi Xunlei,

On 14/11/4 下午10:19, pang.xunlei wrote:
> 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.

I have already do this, my patch merged in tip tree, you can check it.

Regards,
Wanpeng Li

> 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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