From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A8EDFC6778A for ; Tue, 24 Jul 2018 09:56:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BF7D20874 for ; Tue, 24 Jul 2018 09:56:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5BF7D20874 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388359AbeGXLCJ (ORCPT ); Tue, 24 Jul 2018 07:02:09 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46900 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388222AbeGXLCJ (ORCPT ); Tue, 24 Jul 2018 07:02:09 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9C9017A9; Tue, 24 Jul 2018 02:56:26 -0700 (PDT) Received: from e110439-lin (e110439-lin.emea.arm.com [10.4.12.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F2E683F237; Tue, 24 Jul 2018 02:56:23 -0700 (PDT) Date: Tue, 24 Jul 2018 10:56:18 +0100 From: Patrick Bellasi To: Suren Baghdasaryan Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle Subject: Re: [PATCH v2 10/12] sched/core: uclamp: use TG's clamps to restrict Task's clamps Message-ID: <20180724095550.GA3162@e110439-lin> References: <20180716082906.6061-1-patrick.bellasi@arm.com> <20180716082906.6061-11-patrick.bellasi@arm.com> <20180723154025.GF2683@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Archived-At: List-Archive: List-Post: On 23-Jul 10:11, Suren Baghdasaryan wrote: > On Mon, Jul 23, 2018 at 8:40 AM, Patrick Bellasi > wrote: > > On 21-Jul 20:05, Suren Baghdasaryan wrote: > >> On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi [...] > >> So to satisfy both TG and syscall requirements I think you would > >> need to choose the largest value for UCLAMP_MIN and the smallest one > >> for UCLAMP_MAX, meaning the most boosted and most clamped range. > >> Current implementation choses the least boosted value, so > >> effectively one of the UCLAMP_MIN requirements (either from TG or > >> from syscall) are being ignored... Could you please clarify why > >> this choice is made? > > > > The TG values are always used to specify a _restriction_ on > > task-specific values. > > > > Thus, if you look or example at the CPU mask for a task, you can have > > a task with affinity to CPUs 0-1, currently running on a cgroup with > > cpuset.cpus=0... then the task can run only on CPU 0 (althought its > > affinity includes CPU1 too). > > > > Same we do here: if a task has util_min=10, but it's running in a > > cgroup with cpu.util_min=0, then it will not be boosted. > > > > IOW, this allows to implement a "nice" policy at task level, where a > > task (via syscall) can decide to be less boosted with respect to its > > group but never more boosted. The same task can also decide to be more > > clamped, but not less clamped then its current group. > > > > The fact that boost means "at least this much" to me seems like we can > safely choose higher CPU bandwidth (as long as it's lower than > UCLAMP_MAX) I understand your view point, which actually is matching my first implementation for util_min aggregation: https://lore.kernel.org/lkml/20180409165615.2326-5-patrick.bellasi@arm.com/ > but from your description sounds like TG's UCLAMP_MIN means "at most > this much boost" and it's not safe to use CPU bandwidth higher than > TG's UCLAMP_MIN. Indeed, after this discussion with Tejun: https://lore.kernel.org/lkml/20180409222417.GK3126663@devbig577.frc2.facebook.com/ I've convinced myself that for the cgroup interface we have to got for a "restrictive" interface where a parent value must set the upper bound for all its descendants values. AFAIU, that's one of the basic principles of the "delegation model" implemented by cgroups and the common behavior implemented by all controllers. > So instead of specifying min CPU bandwidth for a task it specifies > the max allowed boost. Seems like a discrepancy to me but maybe > there are compelling usecases when this behavior is necessary? I don't think it's strictly related to use-cases, you can always describe a give use-case in one model or the other. It all depends on how you configure your hierarchy and where you place your tasks. For our Android use cases, we are still happy to say that all tasks of a CGroup can be boosted up to a certain value and then we can either: - don't configure tasks: and thus get the CG defined boost - configure a task: and explicitly give back what we don't need This model works quite well with containers, where the parent want to precisely control how much resources are (eventually) usable by a given container. > In that case would be good to spell them out to explain why this > choice is made. Yes, well... if I understand it correctly is really just the recommended way cgroups must be used to re-partition resources. I'll try to better explain this behavior in the changelog for this patch. [...] Best, Patrick -- #include Patrick Bellasi