From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757776AbeD0Iar (ORCPT ); Fri, 27 Apr 2018 04:30:47 -0400 Received: from foss.arm.com ([217.140.101.70]:35722 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757755AbeD0Iap (ORCPT ); Fri, 27 Apr 2018 04:30:45 -0400 Subject: Re: [PATCH 2/2] sched/fair: Avoid calling sync_entity_load_avg() unnecessarily To: Viresh Kumar , Ingo Molnar , Peter Zijlstra Cc: Vincent Guittot , linux-kernel@vger.kernel.org References: <20831b8d237bf3a20e4e328286f678b425ff04c9.1524738578.git.viresh.kumar@linaro.org> From: Dietmar Eggemann Message-ID: Date: Fri, 27 Apr 2018 10:30:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Viresh, On 04/26/2018 12:30 PM, Viresh Kumar wrote: > Call sync_entity_load_avg() directly from find_idlest_cpu() instead of > select_task_rq_fair(), as that's where we need to use task's utilization > value. And call sync_entity_load_avg() only after making sure sched > domain spans over one of the allowed CPUs for the task. > > Signed-off-by: Viresh Kumar The patch looks correct to me but we want to have the waking task synced against its previous rq also for EAS, i.e. for find_energy_efficient_cpu() which will sit next to find_idlest_cpu(). https://marc.info/?l=linux-kernel&m=152302907327168&w=2 The comment on top of the if condition would have to be changed though. I would suggest we leave the call to sync_entity_load_avg() in the slow path of strf() so that we're not forced to call it in find_energy_efficient_cpu(). > --- > kernel/sched/fair.c | 16 +++++++--------- > 1 file changed, 7 insertions(+), 9 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 84fc74ddbd4b..5b1b4f91f132 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6199,6 +6199,13 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p > if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed)) > return prev_cpu; > > + /* > + * We need task's util for capacity_spare_wake, sync it up to prev_cpu's > + * last_update_time. > + */ > + if (!(sd_flag & SD_BALANCE_FORK)) > + sync_entity_load_avg(&p->se); > + > while (sd) { > struct sched_group *group; > struct sched_domain *tmp; > @@ -6651,15 +6658,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f > > if (unlikely(sd)) { > /* Slow path */ > - > - /* > - * We're going to need the task's util for capacity_spare_wake > - * in find_idlest_group. Sync it up to prev_cpu's > - * last_update_time. > - */ > - if (!(sd_flag & SD_BALANCE_FORK)) > - sync_entity_load_avg(&p->se); > - > new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag); > } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ > /* Fast path */ >