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

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Message-ID: <20180706132428.GY2476@hirez.programming.kicks-ass.net>
Date:   Fri, 6 Jul 2018 15:24:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v4 08/12] sched: Add over-utilization/tipping point
 indicator

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?