Re: [PATCH v4 1/6] sched/fair: Fix reschedule which is generated on throttled cfs_rq

[Wanpeng Li]

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 ÐÑ, 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@xxxxxxxxxxxxx>
> > > ---
> > >    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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