From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755570AbeEaQJT (ORCPT ); Thu, 31 May 2018 12:09:19 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:52824 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755456AbeEaQJQ (ORCPT ); Thu, 31 May 2018 12:09:16 -0400 Date: Thu, 31 May 2018 18:08:57 +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 , Patrick Bellasi , Thomas Gleixner Subject: Re: [PATCH v9 3/7] cpuset: Add cpuset.sched.load_balance flag to v2 Message-ID: <20180531160857.GM12180@hirez.programming.kicks-ass.net> References: <1527601294-3444-1-git-send-email-longman@redhat.com> <1527601294-3444-4-git-send-email-longman@redhat.com> <20180531122638.GJ12180@hirez.programming.kicks-ass.net> <42cc1f44-2355-1c0c-b575-49c863303c42@redhat.com> <20180531152050.GK12180@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 31, 2018 at 11:36:39AM -0400, Waiman Long wrote: > > I'm on the fence myself; the only thing I'm fairly sure of is that tying > > this particular behaviour to the load-balance knob seems off. > > The main reason for doing it this way is that I don't want to have > load-balanced partition with no cpu in it. How about we just don't allow > consume-all at all. Each partition must have at least 1 cpu. I suspect that might be sufficient. It certainly is for the use-cases I'm aware of. You always want a system/control set which runs the regular busy work of running a system. Then you have one (or more) partitions to run your 'important' work. > > I also think we should not mix the 'consume all' thing with the > > 'fully-partitioned' thing, as they are otherwise unrelated. > > The "consume all" and "fully-partitioned" look the same to me. Are you > talking about allocating all the CPUs in a partition to sub-partitions > so that there is no CPU left in the parent partition? Not sure what you're asking. "consume all" is allowing sub-partitions to allocate all CPUs of the parent, such that there are none left. "fully-partitioned" is N cpus but no load-balancing, also equivalent to N 1 CPU parititions. They are distinct things. Disabling load-balancing should not affect how many CPUs can be allocated to sub-partitions, the moment you hit 1 CPU the load balancing is effectively off already. Going down to 0 CPUs isn't a problem for the load-balancer, it wasn't doing anything anyway. So the question is if someone really needs the one partition without balancing over N separate paritions.