From patchwork Tue Dec 8 15:35:01 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mel Gorman X-Patchwork-Id: 11958815 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,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 CCF1CC4361B for ; Tue, 8 Dec 2020 15:37:07 +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 8CAD623A7B for ; Tue, 8 Dec 2020 15:37:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8CAD623A7B 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=b1Bfrjmw6QCI7pO6HJM5HGuc4F9ysSAAoA7JNMy+vys=; b=PPHRyded1salsqTspQ+2batzk q8pIHjpIYdr2Biyo3eCGP8VdXdOISVXrHhwgqX7REs75ETanvPpiGeievqEhKswUfcoXy0lYZ2b2M OMn1XEmi3zR1YpYKQ0s5ku+1Ir6pslf04+POcTEDNz7BqzRmv1abLXCBMIwF+mOmbkLecA622orsX GsdfYn78e1wegboGf3ziz4YLrDPxxC+VS2edw26b+KEV3p4lBb6F5b3DkaDP33X54eYol1R1GvdUf Dd0Lb82826kwIazlEH2knHDysUJ6QTemDgAbPnFFdIXNgPWryYY5I1VE8n9G/R3ffqGtVBAO6x4Xs Bj9aghMSw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmf1z-0006pQ-FV; Tue, 08 Dec 2020 15:35:59 +0000 Received: from outbound-smtp48.blacknight.com ([46.22.136.219]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmf1w-0006nx-11 for linux-arm-kernel@lists.infradead.org; Tue, 08 Dec 2020 15:35:57 +0000 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp48.blacknight.com (Postfix) with ESMTPS id 6634AFAC42 for ; Tue, 8 Dec 2020 15:35:54 +0000 (GMT) Received: (qmail 13670 invoked from network); 8 Dec 2020 15:35:54 -0000 Received: from unknown (HELO stampy.112glenside.lan) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPA; 8 Dec 2020 15:35:54 -0000 From: Mel Gorman To: Peter Ziljstra , Ingo Molnar , LKML Subject: [PATCH 4/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Date: Tue, 8 Dec 2020 15:35:01 +0000 Message-Id: <20201208153501.1467-5-mgorman@techsingularity.net> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201208153501.1467-1-mgorman@techsingularity.net> References: <20201208153501.1467-1-mgorman@techsingularity.net> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201208_103556_199022_539653C4 X-CRM114-Status: GOOD ( 15.40 ) 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 , Aubrey Li , 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%* Note that there is a significant corner case. As the SMT scan may be terminated early, not all CPUs have been visited and select_idle_cpu() is still called for a full scan. This case is handled in the next patch. Signed-off-by: Mel Gorman Reviewed-by: Vincent Guittot --- kernel/sched/fair.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 413d895bbbf8..ed6f45832d97 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; @@ -6085,6 +6086,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int idle = false; break; } + + if (idle_candidate == -1 && + cpumask_test_cpu(cpu, p->cpus_ptr)) { + idle_candidate = cpu; + } } if (idle) @@ -6098,7 +6104,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int */ set_idle_cores(target, 0); - return -1; + return idle_candidate; } /*