From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753973AbcHRLqr (ORCPT ); Thu, 18 Aug 2016 07:46:47 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36093 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752520AbcHRLqq (ORCPT ); Thu, 18 Aug 2016 07:46:46 -0400 MIME-Version: 1.0 In-Reply-To: <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> <20160818102438.GA27873@e105550-lin.cambridge.arm.com> From: Wanpeng Li Date: Thu, 18 Aug 2016 19:46:44 +0800 Message-ID: Subject: Re: [PATCH v3 10/13] sched/fair: Compute task/cpu utilization at wake-up more correctly To: Morten Rasmussen Cc: Peter Zijlstra , Ingo Molnar , Dietmar Eggemann , Yuyang Du , Vincent Guittot , Mike Galbraith , sgurrappadi@nvidia.com, Koan-Sin Tan , =?UTF-8?B?5bCP5p6X5pWs5aSq?= , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2016-08-18 18:24 GMT+08:00 Morten Rasmussen : > 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. Maybe this will lead to disable wake affine due to a spike peak value for a low average load task. Regards, Wanpeng Li > > 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 > -- Regards, Wanpeng Li