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 80089C432BE for ; Tue, 10 Aug 2021 14:42:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6805060EB5 for ; Tue, 10 Aug 2021 14:42:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241358AbhHJOmY (ORCPT ); Tue, 10 Aug 2021 10:42:24 -0400 Received: from mga06.intel.com ([134.134.136.31]:43641 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241191AbhHJOmI (ORCPT ); Tue, 10 Aug 2021 10:42:08 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10072"; a="275950409" X-IronPort-AV: E=Sophos;i="5.84,310,1620716400"; d="scan'208";a="275950409" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Aug 2021 07:41:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,310,1620716400"; d="scan'208";a="526170599" Received: from ranerica-svr.sc.intel.com ([172.25.110.23]) by fmsmga002.fm.intel.com with ESMTP; 10 Aug 2021 07:41:45 -0700 From: Ricardo Neri To: "Peter Zijlstra (Intel)" , Ingo Molnar , Juri Lelli , Vincent Guittot Cc: Srikar Dronamraju , Nicholas Piggin , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Len Brown , Srinivas Pandruvada , Tim Chen , Aubrey Li , "Ravi V. Shankar" , Ricardo Neri , "Rafael J. Wysocki" , Quentin Perret , "Joel Fernandes (Google)" , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Ricardo Neri , Aubrey Li , Daniel Bristot de Oliveira Subject: [PATCH v4 6/6] sched/fair: Consider SMT in ASYM_PACKING load balance Date: Tue, 10 Aug 2021 07:41:45 -0700 Message-Id: <20210810144145.18776-7-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210810144145.18776-1-ricardo.neri-calderon@linux.intel.com> References: <20210810144145.18776-1-ricardo.neri-calderon@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When deciding to pull tasks in ASYM_PACKING, it is necessary not only to check for the idle state of the destination CPU, dst_cpu, but also of its SMT siblings. If dst_cpu is idle but its SMT siblings are busy, performance suffers if it pulls tasks from a medium priority CPU that does not have SMT siblings. Implement asym_smt_can_pull_tasks() to inspect the state of the SMT siblings of both dst_cpu and the CPUs in the candidate busiest group. Cc: Aubrey Li Cc: Ben Segall Cc: Daniel Bristot de Oliveira Cc: Dietmar Eggemann Cc: Mel Gorman Cc: Quentin Perret Cc: Rafael J. Wysocki Cc: Srinivas Pandruvada Cc: Steven Rostedt Cc: Tim Chen Reviewed-by: Joel Fernandes (Google) Reviewed-by: Len Brown Signed-off-by: Ricardo Neri --- Changes since v3: * Removed the arch_asym_check_smt_siblings() hook. Discussions with the powerpc folks showed that this patch should not impact them. Also, more recent powerpc processor no longer use asym_packing. (PeterZ) * Removed unnecessary local variable in asym_can_pull_tasks(). (Dietmar) * Removed unnecessary check for local CPUs when the local group has zero utilization. (Joel) * Renamed asym_can_pull_tasks() as asym_smt_can_pull_tasks() to reflect the fact that it deals with SMT cases. * Made asym_smt_can_pull_tasks() return false for !CONFIG_SCHED_SMT so that callers can deal with non-SMT cases. Changes since v2: * Reworded the commit message to reflect updates in code. * Corrected misrepresentation of dst_cpu as the CPU doing the load balancing. (PeterZ) * Removed call to arch_asym_check_smt_siblings() as it is now called in sched_asym(). Changes since v1: * Don't bailout in update_sd_pick_busiest() if dst_cpu cannot pull tasks. Instead, reclassify the candidate busiest group, as it may still be selected. (PeterZ) * Avoid an expensive and unnecessary call to cpumask_weight() when determining if a sched_group is comprised of SMT siblings. (PeterZ). --- kernel/sched/fair.c | 95 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index dd411cefb63f..8a1a2a43732c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8531,10 +8531,99 @@ group_type group_classify(unsigned int imbalance_pct, return group_has_spare; } +/** + * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks + * @dst_cpu: Destination CPU of the load balancing + * @sds: Load-balancing data with statistics of the local group + * @sgs: Load-balancing statistics of the candidate busiest group + * @sg: The candidate busiet group + * + * Check the state of the SMT siblings of both @sds::local and @sg and decide + * if @dst_cpu can pull tasks. If @dst_cpu does not have SMT siblings, it can + * pull tasks if two or more of the SMT siblings of @sg are busy. If only one + * CPU in @sg is busy, pull tasks only if @dst_cpu has higher priority. + * + * If both @dst_cpu and @sg have SMT siblings, even the number of idle CPUs + * between @sds::local and @sg. Thus, pull tasks from @sg if the difference + * between the number of busy CPUs is 2 or more. If the difference is of 1, + * only pull if @dst_cpu has higher priority. If @sg does not have SMT siblings + * only pull tasks if all of the SMT siblings of @dst_cpu are idle and @sg + * has lower priority. + */ +static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds, + struct sg_lb_stats *sgs, + struct sched_group *sg) +{ +#ifdef CONFIG_SCHED_SMT + bool local_is_smt, sg_is_smt; + int sg_busy_cpus; + + local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY; + sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY; + + sg_busy_cpus = sgs->group_weight - sgs->idle_cpus; + + if (!local_is_smt) { + /* + * If we are here, @dst_cpu is idle and does not have SMT + * siblings. Pull tasks if candidate group has two or more + * busy CPUs. + */ + if (sg_is_smt && sg_busy_cpus >= 2) + return true; + + /* + * @dst_cpu does not have SMT siblings. @sg may have SMT + * siblings and only one is busy. In such case, @dst_cpu + * can help if it has higher priority and is idle. + */ + return !sds->local_stat.group_util && + sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); + } + + /* @dst_cpu has SMT siblings. */ + + if (sg_is_smt) { + int local_busy_cpus = sds->local->group_weight - + sds->local_stat.idle_cpus; + int busy_cpus_delta = sg_busy_cpus - local_busy_cpus; + + /* Local can always help to even the number busy CPUs. */ + if (busy_cpus_delta >= 2) + return true; + + if (busy_cpus_delta == 1) + return sched_asym_prefer(dst_cpu, + sg->asym_prefer_cpu); + + return false; + } + + /* + * @sg does not have SMT siblings. Ensure that @sds::local does not end + * up with more than one busy SMT sibling and only pull tasks if there + * are not busy CPUs. As CPUs move in and out of idle state frequently, + * also check the group utilization to smoother the decision. + */ + if (!sds->local_stat.group_util) + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); + + return false; +#else + /* Always return false so that callers deal with non-SMT cases. */ + return false; +#endif +} + static inline bool sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs, struct sched_group *group) { + /* Only do SMT checks if either local or candidate have SMT siblings */ + if ((sds->local->flags & SD_SHARE_CPUCAPACITY) || + (group->flags & SD_SHARE_CPUCAPACITY)) + return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group); + return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu); } @@ -9540,6 +9629,12 @@ static struct rq *find_busiest_queue(struct lb_env *env, nr_running == 1) continue; + /* Make sure we only pull tasks from a CPU of lower priority */ + if ((env->sd->flags & SD_ASYM_PACKING) && + sched_asym_prefer(i, env->dst_cpu) && + nr_running == 1) + continue; + switch (env->migration_type) { case migrate_load: /* -- 2.17.1