Re: [PATCH 2/2] sched/deadline: fix start high-res preemption tick for a non-running task

[Wanpeng Li]

Hi Juri,
On 11/13/14, 5:37 PM, Juri Lelli wrote:
> Hi,
>
> not sure I understand what the problem is here.
>
> On 11/11/14 01:52, Wanpeng Li wrote:
> > Queued ticks are scheduled to match the budget, which means the budget
> > is overall consumed and the dl task should be throttled.
> ... enforce the budget? It means that when the budget is consumed the
> task has to be throttled...

Agreed.

> > Dl task will
> > be replenished immediately if fail to start a dl timer.
> >
> > However, the curr maybe not the left most dl task in the rb tree any
> > more after this immediately replenished and reschedule is needed.
> > Start high-res preemption tick for this upcoming rescheduled dl task
> > is not correct.
> So, the task that is going to preempt curr is picked by
> pick_next_task_dl(), that correctly starts the hrtick for this new task.
>
> Maybe you can add more information about what you are seeing? A callpath
> maybe?

The parameter of task_tick_dl() queued == 1 means that hrtick is fired. 
hrtick() => task_tick_dl( , ,1), so p->dl.runtime should be <= 0 if 
queued == 1. What I see is queued == 1 && p->dl.runtime > 0 && p is not 
the left most task and hrtick is start for this task.

Regards,
Wanpeng Li

> Thanks,
>
> - Juri
>
> > This patch fix it by not starting high-res preemption tick for a
> > non-running dl task.
> >
> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
> > ---
> >   kernel/sched/deadline.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 56674f6..2a6a5bb 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -1090,7 +1090,8 @@ static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
> >   {
> >   	update_curr_dl(rq);
> >   
> > -	if (hrtick_enabled(rq) && queued && p->dl.runtime > 0)
> > +	if (hrtick_enabled(rq) && queued && p->dl.runtime > 0 &&
> > +	    is_leftmost(p, &rq->dl))
> >   		start_hrtick_dl(rq, p);
> >   }
> >   
> --
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