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=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 04FABC433E0 for ; Tue, 26 Jan 2021 05:10:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C53F722B2C for ; Tue, 26 Jan 2021 05:10:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726672AbhAZFKI (ORCPT ); Tue, 26 Jan 2021 00:10:08 -0500 Received: from outbound-smtp48.blacknight.com ([46.22.136.219]:51375 "EHLO outbound-smtp48.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726686AbhAYJcb (ORCPT ); Mon, 25 Jan 2021 04:32:31 -0500 Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp48.blacknight.com (Postfix) with ESMTPS id 8236037A967 for ; Mon, 25 Jan 2021 08:59:10 +0000 (GMT) Received: (qmail 12078 invoked from network); 25 Jan 2021 08:59:10 -0000 Received: from unknown (HELO stampy.112glenside.lan) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPA; 25 Jan 2021 08:59:10 -0000 From: Mel Gorman To: Peter Zijlstra , Ingo Molnar Cc: Vincent Guittot , Li Aubrey , Qais Yousef , LKML , Mel Gorman Subject: [PATCH v4 0/4] Scan for an idle sibling in a single pass Date: Mon, 25 Jan 2021 08:59:05 +0000 Message-Id: <20210125085909.4600-1-mgorman@techsingularity.net> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Changelog since v3 o Drop scanning based on cores, SMT4 results showed problems Changelog since v2 o Remove unnecessary parameters o Update nr during scan only when scanning for cpus Changlog since v1 o Move extern declaration to header for coding style o Remove unnecessary parameter from __select_idle_cpu This series of 4 patches reposts three patches from Peter entitled "select_idle_sibling() wreckage". It only scans the runqueues in a single pass when searching for an idle sibling. Three patches from Peter were dropped. The first patch altered how scan depth was calculated. Scan depth deletion is a random number generator with two major limitations. The avg_idle time is based on the time between a CPU going idle and being woken up clamped approximately by 2*sysctl_sched_migration_cost. This is difficult to compare in a sensible fashion to avg_scan_cost. The second issue is that only the avg_scan_cost of scan failures is recorded and it does not decay. This requires deeper surgery that would justify a patch on its own although Peter notes that https://lkml.kernel.org/r/20180530143105.977759909@infradead.org is potentially useful for an alternative avg_idle metric. The second patch dropped scanned based on cores instead of CPUs as it rationalised the difference between core scanning and CPU scanning. Unfortunately, Vincent reported problems with SMT4 so it's dropped for now until depth searching can be fixed. The third patch dropped converted the idle core scan throttling mechanism to SIS_PROP. While this would unify the throttling of core and CPU scanning, it was not free of regressions and has_idle_cores is a fairly effective throttling mechanism with the caveat that it can have a lot of false positives for workloads like hackbench. Peter's series tried to solve three problems at once, this subset addresses one problem. losses but won more than it lost across a range of workloads and machines. kernel/sched/fair.c | 153 +++++++++++++++++++--------------------- kernel/sched/features.h | 1 - 2 files changed, 72 insertions(+), 82 deletions(-) -- 2.26.2