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 9FF1EC432C3 for ; Fri, 15 Nov 2019 18:48:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E0B02072D for ; Fri, 15 Nov 2019 18:48:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727016AbfKOSsz (ORCPT ); Fri, 15 Nov 2019 13:48:55 -0500 Received: from foss.arm.com ([217.140.110.172]:35346 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726661AbfKOSsy (ORCPT ); Fri, 15 Nov 2019 13:48:54 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DA4E930E; Fri, 15 Nov 2019 10:48:53 -0800 (PST) Received: from [10.0.2.15] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 028533F534; Fri, 15 Nov 2019 10:48:51 -0800 (PST) Subject: Re: [PATCH v2] sched/topology, cpuset: Account for housekeeping CPUs to avoid empty cpumasks To: =?UTF-8?Q?Michal_Koutn=c3=bd?= Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, lizefan@huawei.com, tj@kernel.org, hannes@cmpxchg.org, mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, Dietmar.Eggemann@arm.com, morten.rasmussen@arm.com, qperret@google.com References: <20191104003906.31476-1-valentin.schneider@arm.com> <20191115171807.GH19372@blackbody.suse.cz> From: Valentin Schneider Message-ID: Date: Fri, 15 Nov 2019 18:48:43 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191115171807.GH19372@blackbody.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/11/2019 17:18, Michal Koutný wrote: > Hello. > > On Thu, Nov 14, 2019 at 04:03:50PM +0000, Valentin Schneider wrote: >> Michal, could I nag you for a reviewed-by? I'd feel a bit more confident >> with any sort of approval from folks who actually do use cpusets. > TL;DR I played with the v5.4-rc6 _without_ this fixup and I conclude it > unnecessary (IOW my previous theoretical observation was wrong). > Thanks for going through the trouble of testing the thing. > > The original problem is non-issue with v2 cpuset controller, because > effective_cpus are never empty. isolcpus doesn't take out cpuset CPUs, > hotplug does. In the case, no online CPU remains in the cpuset, it > inherits ancestor's non-empty cpuset. > But we still take out the isolcpus from the domain span before handing it over to the scheduler: cpumask_or(dp, dp, b->effective_cpus); cpumask_and(dp, dp, housekeeping_cpumask(HK_FLAG_DOMAIN)); But... > I reproduced the problem with v1 (before your fix). However, in v1 > effective == allowed (we're destructive and overwrite allowed on > hotunplug) and we already check the emptiness of > > cpumask_intersects(cp->cpus_allowed, housekeeping_cpumask(HK_FLAG_DOMAIN) > > few lines higher. I.e. the fixup adds redundant check against the empty > sched domain production. > ...You're right, I've been misreading that as a '!is_sched_load_balance()' condition ever since. Duh. So this condition will always catch cpusets than only span outside the housekeeping domain, and my previous fixup will catch newly-empty cpusets (due to HP). Perhaps it would've been cleaner to merge the two, but as things stand this patch isn't needed (as you say). I tried this out to really be sure (8 CPU SMP aarch64 qemu target): cd /sys/fs/cgroup/cpuset mkdir cs1 echo 1 > cs1/cpuset.cpu_exclusive echo 0 > cs1/cpuset.mems echo 0-4 > cs1/cpuset.cpus mkdir cs2 echo 1 > cs2/cpuset.cpu_exclusive echo 0 > cs2/cpuset.mems echo 5-7 > cs2/cpuset.cpus echo 0 > cpuset.sched_load_balance booted with isolcpus=6-7 It seems that creating a cpuset with CPUs only outside the housekeeping domain is forbidden, so I'm creating cs2 with *one* CPU in the domain. When I hotplug it out, nothing dies horribly: echo 0 > /sys/devices/system/cpu/cpu5/online [ 24.688145] CPU5: shutdown [ 24.689438] psci: CPU5 killed. [ 24.714168] allowed=0-4 effective=0-4 housekeeping=0-5 [ 24.714642] allowed=6-7 effective=6-7 housekeeping=0-5 [ 24.715416] CPU5 attaching NULL sched-domain. > Sorry for the noise and HTH, Sure does, thanks! > Michal >