From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752702AbeBAQt6 (ORCPT ); Thu, 1 Feb 2018 11:49:58 -0500 Received: from merlin.infradead.org ([205.233.59.134]:55874 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751800AbeBAQtx (ORCPT ); Thu, 1 Feb 2018 11:49:53 -0500 Date: Thu, 1 Feb 2018 17:49:42 +0100 From: Peter Zijlstra To: Tejun Heo Cc: Ingo Molnar , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Li Zefan , Johannes Weiner Subject: Re: [PATCH v4.15-rc9] sched, cgroup: Don't reject lower cpu.max on ancestors Message-ID: <20180201164942.GC2249@hirez.programming.kicks-ass.net> References: <20180122192618.GA1771050@devbig577.frc2.facebook.com> <20180130102156.GS2249@hirez.programming.kicks-ass.net> <20180130145639.GD1121507@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180130145639.GD1121507@devbig577.frc2.facebook.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 Tue, Jan 30, 2018 at 06:56:39AM -0800, Tejun Heo wrote: > Hello, > > On Tue, Jan 30, 2018 at 11:21:56AM +0100, Peter Zijlstra wrote: > > afaiu the existing code does exactly the opposite, it forces the > > descendants to configure less than the parent allows. > > > > You're taking out an error condition and silently allowing descentant > > misconfiguration. How does that make sense? > > Well, they're upper limits, not strict allocations. The current > behavior implemented by cpu isn't either a strict allocation or upper > limits. It disallows a child from having a value higher than the > parent (allocation-ish) but the sum of the children is allowed to > exceed the parent's (limit-ish). True; but its still weird to have the parent 'promise' something and then retract that 'promise' later. > The combination is rather arbitrary and makes it impossible to > delegate safely (a delegatee can block the delegator from reducing the > amount resource allocated to the delegatee) while not really > protecting against overcommit from descendants either. > > We had this sort of input validations in different controllers all in > their own ways. In most cases, these aren't well thought out and we > can't support things like delegation without aligning controller > behaviors. I suppose.. Acked-by: Peter Zijlstra (Intel)