From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753790AbcHRKYj (ORCPT ); Thu, 18 Aug 2016 06:24:39 -0400 Received: from foss.arm.com ([217.140.101.70]:57207 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752441AbcHRKYi (ORCPT ); Thu, 18 Aug 2016 06:24:38 -0400 Date: Thu, 18 Aug 2016 11:24:39 +0100 From: Morten Rasmussen To: Peter Zijlstra Cc: mingo@redhat.com, dietmar.eggemann@arm.com, yuyang.du@intel.com, vincent.guittot@linaro.org, mgalbraith@suse.de, sgurrappadi@nvidia.com, freedom.tan@mediatek.com, keita.kobayashi.ym@renesas.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 10/13] sched/fair: Compute task/cpu utilization at wake-up more correctly Message-ID: <20160818102438.GA27873@e105550-lin.cambridge.arm.com> References: <1469453670-2660-1-git-send-email-morten.rasmussen@arm.com> <1469453670-2660-11-git-send-email-morten.rasmussen@arm.com> <20160815142342.GV6879@twins.programming.kicks-ass.net> <20160815154237.GE3391@e105550-lin.cambridge.arm.com> <20160818084053.GG3391@e105550-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160818084053.GG3391@e105550-lin.cambridge.arm.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 Thu, Aug 18, 2016 at 09:40:55AM +0100, Morten Rasmussen wrote: > On Mon, Aug 15, 2016 at 04:42:37PM +0100, Morten Rasmussen wrote: > > On Mon, Aug 15, 2016 at 04:23:42PM +0200, Peter Zijlstra wrote: > > > But unlike that function, it doesn't actually use __update_load_avg(). > > > Why not? > > > > Fair question :) > > > > We currently exploit the fact that the task utilization is _not_ updated > > in wake-up balancing to make sure we don't under-estimate the capacity > > requirements for tasks that have slept for a while. If we update it, we > > loose the non-decayed 'peak' utilization, but I guess we could just > > store it somewhere when we do the wake-up decay. > > > > I thought there was a better reason when I wrote the patch, but I don't > > recall right now. I will look into it again and see if we can use > > __update_load_avg() to do a proper update instead of doing things twice. > > AFAICT, we should be able to synchronize the task utilization to the > previous rq utilization using __update_load_avg() as you suggest. The > patch below is should work as a replacement without any changes to > subsequent patches. It doesn't solve the under-estimation issue, but I > have another patch for that. And here is a possible solution to the under-estimation issue. The patch would have to go at the end of this set. ---8<--- >>From 5bc918995c6c589b833ba1f189a8b92fa22202ae Mon Sep 17 00:00:00 2001 From: Morten Rasmussen Date: Wed, 17 Aug 2016 15:30:43 +0100 Subject: [PATCH] sched/fair: Track peak per-entity utilization When using PELT (per-entity load tracking) utilization to place tasks at wake-up using the decayed utilization (due to sleep) leads to under-estimation of true utilization of the task. This could mean putting the task on a cpu with less available capacity than is actually needed. This issue can be mitigated by using 'peak' utilization instead of the decayed utilization for placement decisions, e.g. at task wake-up. The 'peak' utilization metric, util_peak, tracks util_avg when the task is running and retains its previous value while the task is blocked/waiting on the rq. It is instantly updated to track util_avg again as soon as the task running again. cc: Ingo Molnar cc: Peter Zijlstra Signed-off-by: Morten Rasmussen --- include/linux/sched.h | 2 +- kernel/sched/fair.c | 18 ++++++++++++++---- 2 files changed, 15 insertions(+), 5 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 4e0c47af9b05..40e427d1d378 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1281,7 +1281,7 @@ struct load_weight { struct sched_avg { u64 last_update_time, load_sum; u32 util_sum, period_contrib; - unsigned long load_avg, util_avg; + unsigned long load_avg, util_avg, util_peak; }; #ifdef CONFIG_SCHEDSTATS diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 11b250531ed4..8462a3d455ff 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -692,6 +692,7 @@ void init_entity_runnable_average(struct sched_entity *se) * At this point, util_avg won't be used in select_task_rq_fair anyway */ sa->util_avg = 0; + sa->util_peak = 0; sa->util_sum = 0; /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */ } @@ -744,6 +745,7 @@ void post_init_entity_util_avg(struct sched_entity *se) } else { sa->util_avg = cap; } + sa->util_peak = sa->util_avg; sa->util_sum = sa->util_avg * LOAD_AVG_MAX; } @@ -2806,6 +2808,9 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, sa->util_avg = sa->util_sum / LOAD_AVG_MAX; } + if (running || sa->util_avg > sa->util_peak) + sa->util_peak = sa->util_avg; + return decayed; } @@ -5174,7 +5179,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, return 1; } -static inline int task_util(struct task_struct *p); +static inline int task_util_peak(struct task_struct *p); static int cpu_util_wake(int cpu, struct task_struct *p); static unsigned long capacity_spare_wake(int cpu, struct task_struct *p) @@ -5257,10 +5262,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, } while (group = group->next, group != sd->groups); /* Found a significant amount of spare capacity. */ - if (this_spare > task_util(p) / 2 && + if (this_spare > task_util_peak(p) / 2 && imbalance*this_spare > 100*most_spare) return NULL; - else if (most_spare > task_util(p) / 2) + else if (most_spare > task_util_peak(p) / 2) return most_spare_sg; if (!idlest || 100*this_load < imbalance*min_load) @@ -5423,6 +5428,11 @@ static inline int task_util(struct task_struct *p) return p->se.avg.util_avg; } +static inline int task_util_peak(struct task_struct *p) +{ + return p->se.avg.util_peak; +} + /* * cpu_util_wake: Compute cpu utilization with any contributions from * the waking task p removed. @@ -5455,7 +5465,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) /* Bring task utilization in sync with prev_cpu */ sync_entity_load_avg(&p->se); - return min_cap * 1024 < task_util(p) * capacity_margin; + return min_cap * 1024 < task_util_peak(p) * capacity_margin; } /* -- 1.9.1