Re: [RFC PATCH v4 08/12] sched: Add over-utilization/tipping point indicator

[Peter Zijlstra]

On Fri, Jul 06, 2018 at 02:20:57PM +0100, Quentin Perret wrote:
> On Friday 06 Jul 2018 at 13:32:08 (+0200), Peter Zijlstra wrote:
> > On Thu, Jun 28, 2018 at 12:40:39PM +0100, Quentin Perret wrote:
> > > @@ -5384,6 +5402,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> > >  {
> > >  	struct cfs_rq *cfs_rq;
> > >  	struct sched_entity *se = &p->se;
> > > +	int task_new = !(flags & ENQUEUE_WAKEUP);
> > >  
> > >  	/*
> > >  	 * The code below (indirectly) updates schedutil which looks at
> > > @@ -5431,8 +5450,12 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> > >  		update_cfs_group(se);
> > >  	}
> > >  
> > > -	if (!se)
> > > +	if (!se) {
> > >  		add_nr_running(rq, 1);
> > > +		if (!task_new)
> > > +			update_overutilized_status(rq);
> > 
> > I'm confused... why only for !ENQUEUE_WAKEUP
> 
> So, what we try to do here is to _not_ set the overutilized flag based
> on the utilization of a new task, because its utilization is 'wrong'.
> That should help avoiding spurious transitions above the overutilized
> threshold.

That most certainly deserves a comment, also didn't util_est fix some of
that wrong-ness?