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Message-ID: <20160617142814.GT30154@twins.programming.kicks-ass.net>
Date: Fri, 17 Jun 2016 16:28:14 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Yuyang Du <yuyang.du@...el.com>, Ingo Molnar <mingo@...nel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Mike Galbraith <umgwanakikbuti@...il.com>,
Benjamin Segall <bsegall@...gle.com>,
Paul Turner <pjt@...gle.com>,
Morten Rasmussen <morten.rasmussen@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks
On Fri, Jun 17, 2016 at 04:09:01PM +0200, Vincent Guittot wrote:
> >
> > Scenario 1: switch to fair class
> >
> > p->sched_class = fair_class;
> > if (queued)
> > enqueue_task(p);
> > ...
> > enqueue_entity()
> > enqueue_entity_load_avg()
> > migrated = !sa->last_update_time (true)
> > if (migrated)
> > attach_entity_load_avg()
> > check_class_changed()
> > switched_from() (!fair)
> > switched_to() (fair)
> > switched_to_fair()
> > attach_entity_load_avg()
> > @@ -733,18 +737,21 @@ void post_init_entity_util_avg(struct sc
> > }
> > sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
> > }
> > +
> > + update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
> > + attach_entity_load_avg(cfs_rq, se);
>
> A new RT task will be attached and will contribute to the load until
> it decays to 0
> Should we detach it for non cfs task ? We just want to update
> last_update_time of RT task to something different from 0
Won't we open up that (scenario 1) hole again? Maybe we can initialize
!fair tasks to 0 load and have them ramp up once they get demoted back
to fair?
Blergh, I'll go ponder moar.
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