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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 1437CCA9EC3 for ; Thu, 31 Oct 2019 10:19:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E02E52086D for ; Thu, 31 Oct 2019 10:19:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727141AbfJaKTK (ORCPT ); Thu, 31 Oct 2019 06:19:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:46124 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726864AbfJaKTK (ORCPT ); Thu, 31 Oct 2019 06:19:10 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id D9028B12E; Thu, 31 Oct 2019 10:19:08 +0000 (UTC) Date: Thu, 31 Oct 2019 10:19:04 +0000 From: Mel Gorman To: Viresh Kumar Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Linux Kernel Mailing List Subject: Re: [PATCH] sched/fair: Make sched-idle cpu selection consistent throughout Message-ID: <20191031101904.GI28938@suse.de> References: <5eba2fb4af9ebc7396101bb9bd6c8aa9c8af0710.1571899508.git.viresh.kumar@linaro.org> <20191030164714.GH28938@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 31, 2019 at 02:42:03PM +0530, Viresh Kumar wrote: > On Wed, 30 Oct 2019 at 22:17, Mel Gorman wrote: > > > As the patch stands, I think a fork-intensive workload where each > > process is doing small amounts of work will suffer from overloading > > domains and have variable performance depending on how quickly the load > > balancer reacts. > > Just wanted to clarify this slightly in case it is confusing. Once a > newly forked > (non SCHED_IDLE) task gets placed on a sched-idle CPU, it won't remain > sched-idle anymore and we will again start looking for a fully idle CPU. So, > we won't put everything on a small set of CPUs, but just one SCHED_NORMAL > task on a CPU unless we are out of idle CPUs. > > Do you have some specific test in mind which I can run to test this ? > Nothing in particular. git test suite for the basic fork-intensive case (mmtests config workload-shellscripts), something fork-intensive but relatively short-lived like a kernel build scaling the number of build jobs (mmtests config config-workload-kerndevel), something fairly basic that scales number of running jobs and relatively long-lived like tbench (mmtests config config-network-tbench). The ideal of course is that you wrote the patch based on an observed problem that you decided to fix. -- Mel Gorman SUSE Labs