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 409EDC4361B for ; Tue, 8 Dec 2020 15:36:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09D0223A69 for ; Tue, 8 Dec 2020 15:36:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730046AbgLHPgQ (ORCPT ); Tue, 8 Dec 2020 10:36:16 -0500 Received: from outbound-smtp48.blacknight.com ([46.22.136.219]:35835 "EHLO outbound-smtp48.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729334AbgLHPgP (ORCPT ); Tue, 8 Dec 2020 10:36:15 -0500 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp48.blacknight.com (Postfix) with ESMTPS id E75BEFA902 for ; Tue, 8 Dec 2020 15:35:23 +0000 (GMT) Received: (qmail 10639 invoked from network); 8 Dec 2020 15:35:23 -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 15:35:23 -0000 From: Mel Gorman To: Peter Ziljstra , Ingo Molnar , LKML Cc: Aubrey Li , Barry Song , Juri Lelli , Vincent Guittot , Valentin Schneider , Linux-ARM , Mel Gorman Subject: [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Date: Tue, 8 Dec 2020 15:34:58 +0000 Message-Id: <20201208153501.1467-2-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 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org SIS_AVG_CPU was introduced as a means of avoiding a search when the average search cost indicated that the search would likely fail. It was a blunt instrument and disabled by 4c77b18cf8b7 ("sched/fair: Make select_idle_cpu() more aggressive") and later replaced with a proportional search depth by 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()"). While there are corner cases where SIS_AVG_CPU is better, it has now been disabled for almost three years. As the intent of SIS_PROP is to reduce the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus on SIS_PROP as a throttling mechanism. Signed-off-by: Mel Gorman --- kernel/sched/fair.c | 20 +++++++++----------- kernel/sched/features.h | 1 - 2 files changed, 9 insertions(+), 12 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 98075f9ea9a8..ac7b34e7372b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6145,7 +6145,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t { struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); struct sched_domain *this_sd; - u64 avg_cost, avg_idle; u64 time; int this = smp_processor_id(); int cpu, nr = INT_MAX; @@ -6154,18 +6153,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t if (!this_sd) return -1; - /* - * Due to large variance we need a large fuzz factor; hackbench in - * particularly is sensitive here. - */ - avg_idle = this_rq()->avg_idle / 512; - avg_cost = this_sd->avg_scan_cost + 1; + if (sched_feat(SIS_PROP)) { + u64 avg_cost, avg_idle, span_avg; - if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost) - return -1; + /* + * Due to large variance we need a large fuzz factor; + * hackbench in particularly is sensitive here. + */ + avg_idle = this_rq()->avg_idle / 512; + avg_cost = this_sd->avg_scan_cost + 1; - if (sched_feat(SIS_PROP)) { - u64 span_avg = sd->span_weight * avg_idle; + span_avg = sd->span_weight * avg_idle; if (span_avg > 4*avg_cost) nr = div_u64(span_avg, avg_cost); else diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 68d369cba9e4..e875eabb6600 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -54,7 +54,6 @@ SCHED_FEAT(TTWU_QUEUE, true) /* * When doing wakeups, attempt to limit superfluous scans of the LLC domain. */ -SCHED_FEAT(SIS_AVG_CPU, false) SCHED_FEAT(SIS_PROP, true) /* -- 2.26.2