From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED12EC433DB for ; Thu, 28 Jan 2021 18:35:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9F6464E47 for ; Thu, 28 Jan 2021 18:35:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232164AbhA1SfL (ORCPT ); Thu, 28 Jan 2021 13:35:11 -0500 Received: from foss.arm.com ([217.140.110.172]:37346 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232138AbhA1Sc4 (ORCPT ); Thu, 28 Jan 2021 13:32:56 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C3E101474; Thu, 28 Jan 2021 10:32:10 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 58F2F3F719; Thu, 28 Jan 2021 10:32:09 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Qais Yousef , Quentin Perret , Pavan Kondeti , Rik van Riel Subject: [PATCH 3/8] sched/fair: Tweak misfit-related capacity checks Date: Thu, 28 Jan 2021 18:31:36 +0000 Message-Id: <20210128183141.28097-4-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210128183141.28097-1-valentin.schneider@arm.com> References: <20210128183141.28097-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org During load-balance, groups classified as group_misfit_task are filtered out if they do not pass group_smaller_max_cpu_capacity(, ); which itself employs fits_capacity() to compare the sgc->max_capacity of both groups. Due to the underlying margin, fits_capacity(X, 1024) will return false for any X > 819. Tough luck, the capacity_orig's on e.g. the Pixel 4 are {261, 871, 1024}. If a CPU-bound task ends up on one of those "medium" CPUs, misfit migration will never intentionally upmigrate it to a CPU of higher capacity due to the aforementioned margin. One may argue the 20% margin of fits_capacity() is excessive in the advent of counter-enhanced load tracking (APERF/MPERF, AMUs), but one point here is that fits_capacity() is meant to compare a utilization value to a capacity value, whereas here it is being used to compare two capacity values. As CPU capacity and task utilization have different dynamics, a sensible approach here would be to add a new helper dedicated to comparing CPU capacities. Introduce capacity_greater(), which uses a 5% margin. Use it to replace the existing capacity checks. Note that check_cpu_capacity() uses yet another margin (sd->imbalance_pct), and is left alone for now. Signed-off-by: Valentin Schneider --- kernel/sched/fair.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7d01fa0bfc7e..58ce0b22fcb0 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -113,6 +113,13 @@ int __weak arch_asym_cpu_priority(int cpu) */ #define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024) +/* + * The margin used when comparing CPU capacities. + * is 'cap' noticeably greater than 'ref' + * + * (default: ~5%) + */ +#define capacity_greater(cap, ref) ((ref) * 1078 < (cap) * 1024) #endif #ifdef CONFIG_CFS_BANDWIDTH @@ -8253,7 +8260,7 @@ check_cpu_capacity(struct rq *rq, struct sched_domain *sd) static inline int check_misfit_status(struct rq *rq, struct sched_domain *sd) { return rq->misfit_task_load && - (rq->cpu_capacity_orig < rq->rd->max_cpu_capacity || + (capacity_greater(rq->rd->max_cpu_capacity, rq->cpu_capacity_orig) || check_cpu_capacity(rq, sd)); } @@ -8352,7 +8359,7 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs) static inline bool group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) { - return fits_capacity(sg->sgc->min_capacity, ref->sgc->min_capacity); + return capacity_greater(ref->sgc->min_capacity, sg->sgc->min_capacity); } /* @@ -8362,7 +8369,7 @@ group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) static inline bool group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref) { - return fits_capacity(sg->sgc->max_capacity, ref->sgc->max_capacity); + return capacity_greater(ref->sgc->max_capacity, sg->sgc->max_capacity); } static inline enum @@ -9421,7 +9428,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, * average load. */ if (sd_has_asym_cpucapacity(env->sd) && - capacity_of(env->dst_cpu) < capacity && + !capacity_greater(capacity_of(env->dst_cpu), capacity) && nr_running == 1) continue; -- 2.27.0