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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 74E97C2BB3F for ; Mon, 7 Dec 2020 17:11:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47C212388C for ; Mon, 7 Dec 2020 17:11:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726890AbgLGRLQ (ORCPT ); Mon, 7 Dec 2020 12:11:16 -0500 Received: from outbound-smtp48.blacknight.com ([46.22.136.219]:47191 "EHLO outbound-smtp48.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725863AbgLGRLQ (ORCPT ); Mon, 7 Dec 2020 12:11:16 -0500 Received: from mail.blacknight.com (pemlinmail06.blacknight.ie [81.17.255.152]) by outbound-smtp48.blacknight.com (Postfix) with ESMTPS id 48CF3FA7DA for ; Mon, 7 Dec 2020 17:10:24 +0000 (GMT) Received: (qmail 9767 invoked from network); 7 Dec 2020 17:10:23 -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); 7 Dec 2020 17:10:23 -0000 Date: Mon, 7 Dec 2020 17:10:21 +0000 From: Mel Gorman To: Peter Zijlstra Cc: Aubrey Li , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, valentin.schneider@arm.com, qais.yousef@arm.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org, Mel Gorman , Jiang Biao Subject: Re: [RFC PATCH v5] sched/fair: select idle cpu from idle cpumask for task wakeup Message-ID: <20201207171021.GF3371@techsingularity.net> References: <20201118043113.53128-1-aubrey.li@linux.intel.com> <20201207155015.GQ3040@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20201207155015.GQ3040@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 04:50:15PM +0100, Peter Zijlstra wrote: > On Wed, Nov 18, 2020 at 12:31:13PM +0800, Aubrey Li wrote: > > Add idle cpumask to track idle cpus in sched domain. When a CPU > > enters idle, if the idle driver indicates to stop tick, this CPU > > is set in the idle cpumask to be a wakeup target. And if the CPU > > is not in idle, the CPU is cleared in idle cpumask during scheduler > > tick to ratelimit idle cpumask update. > > So this will only have SIS consider CPUs that have the tick stopped? > That might affect the facebook tail-latency workloads quite a bit. > This is the concern I had as well. That's why patch "sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling" was created. The intent was that a mask could be used as a hint about what runqueues to look at first but continue looking at other runqueues without examining the same runqueue twice. While the patch would not be merged on its own, it may still be relevant in the context of an idle CPU mask depending on how up to date it is. -- Mel Gorman SUSE Labs