From patchwork Thu Dec 3 14:11:18 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mel Gorman X-Patchwork-Id: 11948937 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=-18.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 D50A4C433C1 for ; Thu, 3 Dec 2020 14:13:01 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6B63720798 for ; Thu, 3 Dec 2020 14:13:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B63720798 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To:Message-Id:Date: Subject:To:From:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=oubLeose4pM/gNn7LXm0VDJd/XJx/Ct2QWRDrr4FwRE=; b=PdJPslWcwsfdP4rm7eTa1N3/W NgdgMNL0us+Uns2kL2S1Ypafm6lckgYhf4u5w4GoNkpEec+xuq699PAGswbqcRdCymq3TfP5PZivx DVN0Zb1i72w2Of06qM+kR2be9F2GG9EInXcIXPPF5ZSP8LZYWgCNF8d0m6Qot3ziQc/3jqYhJioSg W8w4OzF1wCWNTCtkVsMiEQhijyODpLHISJwLSIzsW1bRemVx6bqnzn/tdTDWeVvj9LiKRVSotqnX0 snb8EuodRdpzmwPATVLFXgYT0OagQpIJAkRLPaFYeH9NTTsOSKcNIeBmyiIA2dB6m7c5SnkRFZfsl v+6qBoXPw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkpKb-0003mM-RL; Thu, 03 Dec 2020 14:11:37 +0000 Received: from outbound-smtp19.blacknight.com ([46.22.139.246]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkpKS-0003gg-Ks for linux-arm-kernel@lists.infradead.org; Thu, 03 Dec 2020 14:11:30 +0000 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp19.blacknight.com (Postfix) with ESMTPS id 984681C373A 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201203_091128_827318_08395EDD X-CRM114-Status: GOOD ( 15.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Barry Song , Juri Lelli , Vincent Guittot , Peter Ziljstra , Aubrey Li , Ingo Molnar , Mel Gorman , Valentin Schneider , Linux-ARM Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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; } /*