linux-kernel - Re: [PATCH 04/16] sched/fair: Optimize find_idlest

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Date:	Tue, 24 May 2016 10:12:00 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	peterz@...radead.org, mingo@...hat.com, dietmar.eggemann@....com,
	yuyang.du@...el.com, vincent.guittot@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/16] sched/fair: Optimize find_idlest_cpu() when there
 is no choice

On Tue, 2016-05-24 at 09:05 +0100, Morten Rasmussen wrote:
> On Tue, May 24, 2016 at 08:29:05AM +0200, Mike Galbraith wrote:
> >  
> > > +> > > > 	> > > > /* Check if we have any choice */
> > > +> > > > 	> > > > if (group->group_weight == 1) {
> > > +> > > > 	> > > > > > > 	> > > > return cpumask_first(sched_group_cpus(group));
> > > +> > > > 	> > > > }
> > > +
> > 
> > Hm, if task isn't allowed there, too bad?
> 
> Is that possible for single-cpu groups? I thought we skipped groups with
> no cpus allowed in find_idlest_group():
> 
>                 /* Skip over this group if it has no CPUs allowed */
>                 if (!cpumask_intersects(sched_group_cpus(group),
>                                         tsk_cpus_allowed(p)))
>                         continue;
> 
> Since the group has at least one cpu allowed and only contains one cpu,
> that cpu must be allowed. No?

Yup, you're right, handled before we got there.

	-Mike