From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932222AbcEXIF1 (ORCPT ); Tue, 24 May 2016 04:05:27 -0400 Received: from foss.arm.com ([217.140.101.70]:55251 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932126AbcEXIFU (ORCPT ); Tue, 24 May 2016 04:05:20 -0400 Date: Tue, 24 May 2016 09:05:58 +0100 From: Morten Rasmussen To: Mike Galbraith Cc: peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.com, yuyang.du@intel.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/16] sched/fair: Optimize find_idlest_cpu() when there is no choice Message-ID: <20160524080557.GD27946@e105550-lin.cambridge.arm.com> References: <1464001138-25063-1-git-send-email-morten.rasmussen@arm.com> <1464001138-25063-5-git-send-email-morten.rasmussen@arm.com> <1464071345.3743.22.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464071345.3743.22.camel@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > cc: Peter Zijlstra > > > > Signed-off-by: Morten Rasmussen > > --- > > 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?