From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966320AbeEXPRE (ORCPT ); Thu, 24 May 2018 11:17:04 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:52073 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966258AbeEXPRB (ORCPT ); Thu, 24 May 2018 11:17:01 -0400 X-Google-Smtp-Source: AB8JxZrc/RP/+OVSz8XnpEBM5HOnYpzC9KL5xypbJYAa6HFyY3EzPr5G1h4N1P07g/q20HoU9QRRuw== Date: Thu, 24 May 2018 17:16:56 +0200 From: Juri Lelli To: Waiman Long Cc: Tejun Heo , Li Zefan , Johannes Weiner , Peter Zijlstra , Ingo Molnar , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@fb.com, pjt@google.com, luto@amacapital.net, Mike Galbraith , torvalds@linux-foundation.org, Roman Gushchin Subject: Re: [PATCH v8 3/6] cpuset: Add cpuset.sched.load_balance flag to v2 Message-ID: <20180524151656.GD3948@localhost.localdomain> References: <1526590545-3350-1-git-send-email-longman@redhat.com> <1526590545-3350-4-git-send-email-longman@redhat.com> <20180524143614.GC3948@localhost.localdomain> <4bd31510-4f73-e263-8dc1-5edb0fe63b59@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4bd31510-4f73-e263-8dc1-5edb0fe63b59@redhat.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/05/18 11:09, Waiman Long wrote: > On 05/24/2018 10:36 AM, Juri Lelli wrote: > > On 17/05/18 16:55, Waiman Long wrote: > > > > [...] > > > >> + A parent cgroup cannot distribute all its CPUs to child > >> + scheduling domain cgroups unless its load balancing flag is > >> + turned off. > >> + > >> + cpuset.sched.load_balance > >> + A read-write single value file which exists on non-root > >> + cpuset-enabled cgroups. It is a binary value flag that accepts > >> + either "0" (off) or a non-zero value (on). This flag is set > >> + by the parent and is not delegatable. > >> + > >> + When it is on, tasks within this cpuset will be load-balanced > >> + by the kernel scheduler. Tasks will be moved from CPUs with > >> + high load to other CPUs within the same cpuset with less load > >> + periodically. > >> + > >> + When it is off, there will be no load balancing among CPUs on > >> + this cgroup. Tasks will stay in the CPUs they are running on > >> + and will not be moved to other CPUs. > >> + > >> + The initial value of this flag is "1". This flag is then > >> + inherited by child cgroups with cpuset enabled. Its state > >> + can only be changed on a scheduling domain cgroup with no > >> + cpuset-enabled children. > > [...] > > > >> + /* > >> + * On default hierachy, a load balance flag change is only allowed > >> + * in a scheduling domain with no child cpuset. > >> + */ > >> + if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) && balance_flag_changed && > >> + (!is_sched_domain(cs) || css_has_online_children(&cs->css))) { > >> + err = -EINVAL; > >> + goto out; > >> + } > > The rule is actually > > > > - no child cpuset > > - and it must be a scheduling domain > > > > Right? > > Yes, because it doesn't make sense to have a cpu in one cpuset that has > loading balance off while, at the same time, in another cpuset with load > balancing turned on. This restriction is there to make sure that the > above condition will not happen. I may be wrong if there is a realistic > use case where the above condition is desired. Yep, makes sense to me. Maybe add the second condition to the comment and documentation.