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

[Wanpeng Li]

Hi Juri,
On 11/17/14, 5:50 PM, Juri Lelli wrote:
> Hi,
>
> On 13/11/14 10:30, Wanpeng Li wrote:
> > 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.
> Oh, right, now it makes sense. Good catch! :)
>
> Could you please post a second version with a more explanatory changelog
> and maybe a comment just above the check?

Ok, I will do it and send out a new version tomorrow. ;-) Btw, could you 
review this patch? https://lkml.org/lkml/2014/11/13/51 The bug is 
introduced by deadline.

Regards,
Wanpeng Li

>   
> Thanks,
>
> - Juri
>
> > 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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