Re: [PATCH RFC] sched/deadline: Use the revised wakeup rule for suspending constrained dl tasks

[Peter Zijlstra]

On Thu, May 04, 2017 at 04:17:21PM +0200, Peter Zijlstra wrote:
> We use two difference CBS rules:
> 
>  1) the original CBS rule for implicit deadline tasks;
>  2) the revised CBS rule for constrained deadline tasks.

> > @@ -500,6 +550,14 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
> >  
> >  	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
> >  	    dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
> > +
> > +		if (unlikely(dl_is_constrained(dl_se) &&
> > +		    !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
> > +		    !dl_se->dl_boosted)){
> > +			update_dl_revised_wakeup(dl_se, rq);
> > +			return;
> > +		}
> > +
> >  		dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> >  		dl_se->runtime = pi_se->dl_runtime;
> >  	}

That comment above does not match the code. We can still use the
original CBS rule for constrained tasks.

We only use the revised CBS rule when the constrained task hasn't missed
its deadline yet.