Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756500AbcJNNmS (ORCPT ); Fri, 14 Oct 2016 09:42:18 -0400 Received: from foss.arm.com ([217.140.101.70]:37702 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756429AbcJNNmQ (ORCPT ); Fri, 14 Oct 2016 09:42:16 -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 4/6] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Date: Fri, 14 Oct 2016 14:41:10 +0100 Message-Id: <1476452472-24740-5-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: 2088 Lines: 62 For asymmetric cpu capacity systems it is counter-productive for throughput if low capacity cpus are pulling tasks from non-overloaded cpus with higher capacity. The assumption is that higher cpu capacity is preferred over running alone in a group with lower cpu capacity. This patch rejects higher cpu capacity groups with one or less task per cpu as potential busiest group which could otherwise lead to a series of failing load-balancing attempts leading to a force-migration. cc: Ingo Molnar cc: Peter Zijlstra Signed-off-by: Morten Rasmussen --- kernel/sched/fair.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 28e42cb41d7b..a5efafda23ef 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7069,6 +7069,17 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs) return false; } +/* + * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller + * per-cpu capacity than sched_group ref. + */ +static inline bool +group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref) +{ + return sg->sgc->min_capacity * capacity_margin < + ref->sgc->min_capacity * 1024; +} + static inline enum group_type group_classify(struct sched_group *group, struct sg_lb_stats *sgs) @@ -7172,6 +7183,20 @@ static bool update_sd_pick_busiest(struct lb_env *env, if (sgs->avg_load <= busiest->avg_load) return false; + if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) + goto asym_packing; + + /* + * Candidate sg has no more than one task per cpu and + * has higher per-cpu capacity. Migrating tasks to less + * capable cpus may harm throughput. Maximize throughput, + * power/energy consequences are not considered. + */ + if (sgs->sum_nr_running <= sgs->group_weight && + group_smaller_cpu_capacity(sds->local, sg)) + return false; + +asym_packing: /* This is the busiest node in its class. */ if (!(env->sd->flags & SD_ASYM_PACKING)) return true; -- 2.7.4