Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756642AbcJNNm1 (ORCPT ); Fri, 14 Oct 2016 09:42:27 -0400 Received: from foss.arm.com ([217.140.101.70]:37732 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756454AbcJNNmS (ORCPT ); Fri, 14 Oct 2016 09:42:18 -0400 From: Morten Rasmussen To: peterz@infradead.org, mingo@redhat.com Cc: 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, Morten Rasmussen Subject: [PATCH v5 5/6] sched/fair: Track peak per-entity utilization Date: Fri, 14 Oct 2016 14:41:11 +0100 Message-Id: <1476452472-24740-6-git-send-email-morten.rasmussen@arm.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1476452472-24740-1-git-send-email-morten.rasmussen@arm.com> References: <1476452472-24740-1-git-send-email-morten.rasmussen@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4157 Lines: 117 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 | 23 +++++++++++++++++------ 2 files changed, 18 insertions(+), 7 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index ad51978ff15e..988d7f48604e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1294,7 +1294,7 @@ 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 a5efafda23ef..e0abff77764f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -696,6 +696,7 @@ 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 */ } @@ -747,6 +748,7 @@ 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; } @@ -3515,6 +3517,10 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) */ if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE) update_min_vruntime(cfs_rq); + + /* Save peak PELT utilization for task to help wake-up decisions */ + if (flags & DEQUEUE_SLEEP && entity_is_task(se)) + se->avg.util_peak = se->avg.util_avg; } /* @@ -5203,7 +5209,7 @@ 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) @@ -5286,14 +5292,14 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, /* * The cross-over point between using spare capacity or least load * is too conservative for high utilization tasks on partially - * utilized systems if we require spare_capacity > task_util(p), + * utilized systems if we require spare_capacity > task_util_peak(p), * so we allow for some task stuffing by using - * spare_capacity > task_util(p)/2. + * spare_capacity > task_util_peak(p)/2. */ - 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) @@ -5628,6 +5634,11 @@ 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. @@ -5667,7 +5678,7 @@ 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; } /* -- 2.7.4