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Message-ID: <20160524080557.GD27946@e105550-lin.cambridge.arm.com> Date: Tue, 24 May 2016 09:05:58 +0100 From: Morten Rasmussen <morten.rasmussen@....com> To: Mike Galbraith <umgwanakikbuti@...il.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, May 24, 2016 at 08:29:05AM +0200, Mike Galbraith wrote: > On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen wrote: > > In the current find_idlest_group()/find_idlest_cpu() search we end up > > calling find_idlest_cpu() in a sched_group containing only one cpu in > > the end. Checking idle-states becomes pointless when there is no > > alternative, so bail out instead. > > > > cc: Ingo Molnar <mingo@...hat.com> > > cc: Peter Zijlstra <peterz@...radead.org> > > > > Signed-off-by: Morten Rasmussen <morten.rasmussen@....com> > > --- > > kernel/sched/fair.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 0fe3020..564215d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5155,6 +5155,11 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) > > > > int shallowest_idle_cpu = -1; > > > > int i; > > > > +> > /* 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?
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