From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH v4.15-rc9] sched, cgroup: Don't reject lower cpu.max on ancestors Date: Tue, 30 Jan 2018 06:56:39 -0800 Message-ID: <20180130145639.GD1121507@devbig577.frc2.facebook.com> References: <20180122192618.GA1771050@devbig577.frc2.facebook.com> <20180130102156.GS2249@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=jE4un1YQvFyyNrXjA4HtlOUYbWBNhzPJull+C6KKWIU=; b=uCEOmcfNjCP8jgx5q2mffxTkut16lW9bO3rmigEv/jzH+J+1U8EGZpypGsyNZcFp8I ixA0iBAU+/KLLxWONpaXyTmOeMClVXbabYIUJS+FLJcSVneU2FmCPd0XUP2WSIrsgk0J j6s3W1FKxni4A/l8bj4acmLtZoMyaPfjSb3Vcd+LBz1YKNrpiHv5I3UZoBOoQv/9LMeX 2bI9R6Ond7ZOUh7kplN6dCIeZmGAanlC7psJgIHKLPHgqPN40RV7oNKIgu5O5Fjo5jKI Q65weW57Xiof3xxBnEiasNyheHrTRKetL2hpSETv4B66ggAnJkIPTuIsOBG9l2Dvgmd1 +4pA== Content-Disposition: inline In-Reply-To: <20180130102156.GS2249@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Li Zefan , Johannes Weiner 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). 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. Thanks. -- tejun