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=-16.8 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 4B865C433B4 for ; Wed, 7 Apr 2021 22:06:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0058F61205 for ; Wed, 7 Apr 2021 22:06:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230307AbhDGWG5 (ORCPT ); Wed, 7 Apr 2021 18:06:57 -0400 Received: from foss.arm.com ([217.140.110.172]:35784 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230142AbhDGWGx (ORCPT ); Wed, 7 Apr 2021 18:06:53 -0400 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 57CDE1474; Wed, 7 Apr 2021 15:06:43 -0700 (PDT) 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 C64843F792; Wed, 7 Apr 2021 15:06:41 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Qais Yousef , Vincent Guittot , Dietmar Eggemann , Lingutla Chandrasekhar , Peter Zijlstra , Ingo Molnar , Morten Rasmussen , Quentin Perret , Pavan Kondeti , Rik van Riel Subject: [PATCH v5 3/3] sched/fair: Introduce a CPU capacity comparison helper Date: Wed, 7 Apr 2021 23:06:28 +0100 Message-Id: <20210407220628.3798191-4-valentin.schneider@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210407220628.3798191-1-valentin.schneider@arm.com> References: <20210407220628.3798191-1-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. Also note that comparing capacity extrema of local and source sched_group's doesn't make much sense when at the day of the day the imbalance will be pulled by a known env->dst_cpu, whose capacity can be anywhere within the local group's capacity extrema. While at it, replace group_smaller_{min, max}_cpu_capacity() with comparisons of the source group's min/max capacity and the destination CPU's capacity. Signed-off-by: Valentin Schneider Reviewed-by: Qais Yousef Reviewed-by: Vincent Guittot Reviewed-by: Dietmar Eggemann Tested-by: Lingutla Chandrasekhar --- kernel/sched/fair.c | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d8077f82a380..c9c5c2697998 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 'cap1' noticeably greater than 'cap2' + * + * (default: ~5%) + */ +#define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078) #endif #ifdef CONFIG_CFS_BANDWIDTH @@ -8364,26 +8371,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs) return false; } -/* - * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller - * per-CPU capacity than sched_group ref. - */ -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); -} - -/* - * group_smaller_max_cpu_capacity: Returns true if sched_group sg has smaller - * per-CPU capacity_orig than 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); -} - static inline enum group_type group_classify(unsigned int imbalance_pct, struct sched_group *group, @@ -8539,7 +8526,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, * internally or be covered by avg_load imbalance (eventually). */ if (sgs->group_type == group_misfit_task && - (!group_smaller_max_cpu_capacity(sg, sds->local) || + (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || sds->local_stat.group_type != group_has_spare)) return false; @@ -8623,7 +8610,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, */ if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && (sgs->group_type <= group_fully_busy) && - (group_smaller_min_cpu_capacity(sds->local, sg))) + (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) return false; return true; @@ -9423,7 +9410,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, * average load. */ if (env->sd->flags & SD_ASYM_CPUCAPACITY && - capacity_of(env->dst_cpu) < capacity && + !capacity_greater(capacity_of(env->dst_cpu), capacity) && nr_running == 1) continue; -- 2.25.1