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SubjectRe: [PATCH v4 1/6] sched/fair: Fix reschedule which is generated on throttled cfs_rq
Hi Kirill,
10/24/14, 2:01 PM, Kirill Tkhai:
> Hi, Wanpeng,
>
> the commit commentary confuses, I'm agree. Really it's just a cleanup.
>
> On Пт, 2014-10-24 at 07:27 +0800, Wanpeng Li wrote:
>> Hi Kirill,
>> 8/6/14, 4:06 PM, Kirill Tkhai:
>>> (sched_entity::on_rq == 1) does not guarantee the task is pickable;
>>> changes on throttled cfs_rq must not lead to reschedule.
>> Why (sched_entity::on_rq == 1) doesn't guarantee the task is pickable
>> since entity will be dequeued during throttling cfs_rq?
> Because one of task's (grand)parents in hierarhy may be throtthed and
> dequeued.
>
> But task_struct::on_rq check doesn't guarantee this too. So, just ignore
> commit commentary; the commentary is wrong.
>
>>> Check for task_struct::on_rq instead.
>> Do you mean task_struct::on_rq will be cleared during throttling cfs_rq?
>> I can't find codes do this.
> No, it not cleared. The commit commentary should be:
> "sched: Cleanup. Check task_struct::on_rq instead of sched_entity::on_rq,
> because it is the same for a task"

IIUR, for fair class, sched_entity::on_rq will be set/clear during
enqueue/dequeue, task_struct::on_rq will changed during task migration,
I'm not sure why they are the same.

Regards,
Wanpeng Li

>
>
>> Regards,
>> Wanpeng Li
>>
>>> Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
>>> ---
>>> kernel/sched/fair.c | 6 +++---
>>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index bfa3c86..6f0ce2b 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -7465,7 +7465,7 @@ static void task_fork_fair(struct task_struct *p)
>>> static void
>>> prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
>>> {
>>> - if (!p->se.on_rq)
>>> + if (!p->on_rq)
>>> return;
>>>
>>> /*
>>> @@ -7521,15 +7521,15 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
>>> */
>>> static void switched_to_fair(struct rq *rq, struct task_struct *p)
>>> {
>>> - struct sched_entity *se = &p->se;
>>> #ifdef CONFIG_FAIR_GROUP_SCHED
>>> + struct sched_entity *se = &p->se;
>>> /*
>>> * Since the real-depth could have been changed (only FAIR
>>> * class maintain depth value), reset depth properly.
>>> */
>>> se->depth = se->parent ? se->parent->depth + 1 : 0;
>>> #endif
>>> - if (!se->on_rq)
>>> + if (!p->on_rq)
>>> return;
>>>
>>> /*
>>>
>>>
>>>
>>> --
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