From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v8 3/6] cpuset: Add cpuset.sched.load_balance flag to v2 Date: Thu, 24 May 2018 11:22:13 -0400 Message-ID: <5f409ed7-3850-f1ea-58cf-4326605d1570@redhat.com> 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> <20180524151656.GD3948@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180524151656.GD3948@localhost.localdomain> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Juri Lelli 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 On 05/24/2018 11:16 AM, Juri Lelli wrote: > 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. Sure. Will do. -Longman