From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967962AbeEXPmb (ORCPT ); Thu, 24 May 2018 11:42:31 -0400 Received: from merlin.infradead.org ([205.233.59.134]:48984 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967710AbeEXPmV (ORCPT ); Thu, 24 May 2018 11:42:21 -0400 Date: Thu, 24 May 2018 17:41:56 +0200 From: Peter Zijlstra To: Waiman Long Cc: Tejun Heo , Li Zefan , Johannes Weiner , 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 , Juri Lelli Subject: Re: [PATCH v8 2/6] cpuset: Add new v2 cpuset.sched.domain flag Message-ID: <20180524154156.GI12198@hirez.programming.kicks-ass.net> References: <1526590545-3350-1-git-send-email-longman@redhat.com> <1526590545-3350-3-git-send-email-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1526590545-3350-3-git-send-email-longman@redhat.com> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 17, 2018 at 04:55:41PM -0400, Waiman Long wrote: > A new cpuset.sched.domain boolean flag is added to cpuset v2. This new > flag indicates that the CPUs in the current cpuset should be treated > as a separate scheduling domain. The traditional name for this is a partition. > This new flag is owned by the parent > and will cause the CPUs in the cpuset to be removed from the effective > CPUs of its parent. This is a significant departure from existing behaviour, but one I can appreciate. I don't immediately see something terribly wrong with it. > This is implemented internally by adding a new isolated_cpus mask that > holds the CPUs belonging to child scheduling domain cpusets so that: > > isolated_cpus | effective_cpus = cpus_allowed > isolated_cpus & effective_cpus = 0 > > This new flag can only be turned on in a cpuset if its parent is either > root or a scheduling domain itself with non-empty cpu list. The state > of this flag cannot be changed if the cpuset has children. > > Signed-off-by: Waiman Long > --- > Documentation/cgroup-v2.txt | 22 ++++ > kernel/cgroup/cpuset.c | 237 +++++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 256 insertions(+), 3 deletions(-) > > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt > index cf7bac6..54d9e22 100644 > --- a/Documentation/cgroup-v2.txt > +++ b/Documentation/cgroup-v2.txt > @@ -1514,6 +1514,28 @@ Cpuset Interface Files > it is a subset of "cpuset.mems". Its value will be affected > by memory nodes hotplug events. > > + cpuset.sched.domain > + 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). I would be conservative and only allow 0/1. > This flag is set > + by the parent and is not delegatable. > + > + If set, it indicates that the CPUs in the current cgroup will > + be the root of a scheduling domain. The root cgroup is always > + a scheduling domain. There are constraints on where this flag > + can be set. It can only be set in a cgroup if all the following > + conditions are true. > + > + 1) The parent cgroup is also a scheduling domain with a non-empty > + cpu list. Ah, so initially I was confused by the requirement for root to have it always set, but you'll allow child domains to steal _all_ CPUs, such that root ends up with an empty effective set? What about the (kernel) threads that cannot be moved out of the root group? > + 2) The list of CPUs are exclusive, i.e. they are not shared by > + any of its siblings. Right. > + 3) There is no child cgroups with cpuset enabled. > + > + Setting this flag will take the CPUs away from the effective > + CPUs of the parent cgroup. Once it is set, this flag cannot be > + cleared if there are any child cgroups with cpuset enabled. This I'm not clear on. Why?