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 4CDBEC001B1 for ; Thu, 3 Dec 2020 14:12:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1005F20709 for ; Thu, 3 Dec 2020 14:12:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436567AbgLCOMU (ORCPT ); Thu, 3 Dec 2020 09:12:20 -0500 Received: from outbound-smtp25.blacknight.com ([81.17.249.193]:58408 "EHLO outbound-smtp25.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727358AbgLCOMS (ORCPT ); Thu, 3 Dec 2020 09:12:18 -0500 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp25.blacknight.com (Postfix) with ESMTPS id 92AC3CABC6 for ; Thu, 3 Dec 2020 14:11:25 +0000 (GMT) Received: (qmail 22748 invoked from network); 3 Dec 2020 14:11:25 -0000 Received: from unknown (HELO stampy.112glenside.lan) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPA; 3 Dec 2020 14:11:25 -0000 From: Mel Gorman To: LKML Cc: Aubrey Li , Barry Song , Ingo Molnar , Peter Ziljstra , Juri Lelli , Vincent Guittot , Valentin Schneider , Linux-ARM , Mel Gorman Subject: [PATCH 04/10] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Date: Thu, 3 Dec 2020 14:11:18 +0000 Message-Id: <20201203141124.7391-5-mgorman@techsingularity.net> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201203141124.7391-1-mgorman@techsingularity.net> References: <20201203141124.7391-1-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org select_idle_core is called when SMT is active and there is likely a free core available. It may find idle CPUs but this information is simply discarded and the scan starts over again with select_idle_cpu. This patch caches information on idle CPUs found during the search for a core and uses one if no core is found. This is a tradeoff. There may be a slight impact when utilisation is low and an idle core can be found quickly. It provides improvements as the number of busy CPUs approaches 50% of the domain size when SMT is enabled. With tbench on a 2-socket CascadeLake machine, 80 logical CPUs, HT enabled 5.10.0-rc6 5.10.0-rc6 schedstat idlecandidate Hmean 1 500.06 ( 0.00%) 505.67 * 1.12%* Hmean 2 975.90 ( 0.00%) 974.06 * -0.19%* Hmean 4 1902.95 ( 0.00%) 1904.43 * 0.08%* Hmean 8 3761.73 ( 0.00%) 3721.02 * -1.08%* Hmean 16 6713.93 ( 0.00%) 6769.17 * 0.82%* Hmean 32 10435.31 ( 0.00%) 10312.58 * -1.18%* Hmean 64 12325.51 ( 0.00%) 13792.01 * 11.90%* Hmean 128 21225.21 ( 0.00%) 20963.44 * -1.23%* Hmean 256 20532.83 ( 0.00%) 20335.62 * -0.96%* Hmean 320 20334.81 ( 0.00%) 20147.25 * -0.92%* In this particular test, the cost/benefit is marginal except for 64 which was a point where the machine was over 50% busy but not fully utilised. Signed-off-by: Mel Gorman --- kernel/sched/fair.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fc48cc99b03d..845bc0cd9158 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6066,6 +6066,7 @@ void __update_idle_core(struct rq *rq) */ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target) { + int idle_candidate = -1; struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); int core, cpu; @@ -6084,7 +6085,13 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int schedstat_inc(this_rq()->sis_scanned); if (!available_idle_cpu(cpu)) { idle = false; - break; + if (idle_candidate != -1) + break; + } + + if (idle_candidate == -1 && + cpumask_test_cpu(cpu, p->cpus_ptr)) { + idle_candidate = cpu; } } @@ -6099,7 +6106,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int */ set_idle_cores(target, 0); - return -1; + return idle_candidate; } /* -- 2.26.2