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=-15.2 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_SANE_1 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 E5070C433C1 for ; Thu, 3 Dec 2020 14:20:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 91D5E20793 for ; Thu, 3 Dec 2020 14:20:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730925AbgLCOUa (ORCPT ); Thu, 3 Dec 2020 09:20:30 -0500 Received: from outbound-smtp38.blacknight.com ([46.22.139.221]:45653 "EHLO outbound-smtp38.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728814AbgLCOUa (ORCPT ); Thu, 3 Dec 2020 09:20:30 -0500 Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp38.blacknight.com (Postfix) with ESMTPS id 2C2C9179F for ; Thu, 3 Dec 2020 14:19:38 +0000 (GMT) Received: (qmail 9227 invoked from network); 3 Dec 2020 14:19:38 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 3 Dec 2020 14:19:37 -0000 Date: Thu, 3 Dec 2020 14:19:36 +0000 From: Mel Gorman To: LKML Cc: Aubrey Li , Barry Song , Ingo Molnar , Peter Ziljstra , Juri Lelli , Vincent Guittot , Valentin Schneider , Linux-ARM Subject: [PATCH 09/10] sched/fair: Limit the search for an idle core Message-ID: <20201203141936.GV3371@techsingularity.net> References: <20201203141124.7391-1-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20201203141124.7391-1-mgorman@techsingularity.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Note: This is a bad idea, it's for illustration only to show how the search space can be filtered at each stage. Searching an idle_cpu_mask would be a potential option. select_idle_core() would be left alone as it has its own throttling mechanism select_idle_core() may search a full domain for an idle core even if idle CPUs exist result in an excessive search. This patch partially limits the search for an idle core similar to select_idle_cpu() once an idle candidate is found. Note that this patch can *increase* the number of runqueues considered. Any searching done by select_idle_core() is duplicated by select_idle_cpu() if an idle candidate is not found. If there is an idle CPU then aborting select_idle_core() can have a negative impact. This is addressed in the next patch. Signed-off-by: Mel Gorman --- kernel/sched/fair.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 33ce65b67381..cd95daf9f53e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6095,7 +6095,8 @@ void __update_idle_core(struct rq *rq) * there are no idle cores left in the system; tracked through * sd_llc->shared->has_idle_cores and enabled through update_idle_core() above. */ -static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target) +static int select_idle_core(struct task_struct *p, struct sched_domain *sd, + int target, int nr) { int idle_candidate = -1; struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); @@ -6115,6 +6116,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int for_each_cpu(cpu, cpu_smt_mask(core)) { schedstat_inc(this_rq()->sis_scanned); + + /* Apply limits if there is an idle candidate */ + if (idle_candidate != -1) + nr--; + if (!available_idle_cpu(cpu)) { idle = false; if (idle_candidate != -1) @@ -6130,6 +6136,9 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int if (idle) return core; + if (!nr) + break; + cpumask_andnot(cpus, cpus, cpu_smt_mask(core)); } @@ -6165,7 +6174,8 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t #else /* CONFIG_SCHED_SMT */ -static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target) +static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, + int target, int nr) { return -1; } @@ -6349,7 +6359,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) depth = sis_search_depth(sd, this_sd); schedstat_inc(this_rq()->sis_domain_search); - i = select_idle_core(p, sd, target); + i = select_idle_core(p, sd, target, depth); if ((unsigned)i < nr_cpumask_bits) return i; -- 2.26.2