Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751843AbdH1SXM (ORCPT ); Mon, 28 Aug 2017 14:23:12 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:34380 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751306AbdH1SXI (ORCPT ); Mon, 28 Aug 2017 14:23:08 -0400 Date: Mon, 28 Aug 2017 11:23:03 -0700 From: Tejun Heo To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , "Rafael J . Wysocki" , Paul Turner , Vincent Guittot , John Stultz , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Tim Murray , Todd Kjos , Andres Oportus , Joel Fernandes , Viresh Kumar Subject: Re: [RFCv4 1/6] sched/core: add utilization clamping to CPU controller Message-ID: <20170828182303.GZ491396@devbig577.frc2.facebook.com> References: <20170824180857.32103-1-patrick.bellasi@arm.com> <20170824180857.32103-2-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170824180857.32103-2-patrick.bellasi@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2899 Lines: 68 Hello, No idea whether this makes sense overall. I'll just comment on the cgroup interface part. On Thu, Aug 24, 2017 at 07:08:52PM +0100, Patrick Bellasi wrote: > This patch extends the CPU controller by adding a couple of new attributes, > util_min and util_max, which can be used to enforce frequency boosting and > capping. Specifically: > > - util_min: defines the minimum CPU utilization which should be considered, > e.g. when schedutil selects the frequency for a CPU while a > task in this group is RUNNABLE. > i.e. the task will run at least at a minimum frequency which > corresponds to the min_util utilization > > - util_max: defines the maximum CPU utilization which should be considered, > e.g. when schedutil selects the frequency for a CPU while a > task in this group is RUNNABLE. > i.e. the task will run up to a maximum frequency which > corresponds to the max_util utilization I'm not sure min/max are the right names here. min/low/high/max are used to designate guarantees and limits on resources and the above is more restricting the range of an attribute. I'll think more about what'd be better names here. > These attributes: > a) are tunable at all hierarchy levels, i.e. at root group level too, thus > allowing to defined minimum and maximum frequency constraints for all > otherwise non-classified tasks (e.g. autogroups) The problem with doing the above is two-fold. 1. The feature becomes inaccessible without cgroup even though it doesn't have much to do with cgroup at system level. 2. For the above and other historical reasons, most other features have a separate way to configure at the system level. I think it'd be better to keep the root level control outside cgorup. > b) allow to create subgroups of tasks which are not violating the > utilization constraints defined by the parent group. The problem with doing the above is that it ties the configs of a cgroup with its ancestors and that gets weird across delegation boundaries. Other resource knobs don't behave this way - a descendant cgroup can have any memory.low/high/max values and an ancestor changing config doesn't destory its descendants' configs. Please follow the same convention. > Tasks on a subgroup can only be more boosted and/or capped, which is > matching with the "limits" schema proposed by the "Resource Distribution > Model (RDM)" suggested by the CGroups v2 documentation: > Documentation/cgroup-v2.txt So, the guarantee side (min / low) shouldn't allow the descendants to have more. ie. if memory.low is 512M at the parent, its children can never have more than 512M of low protection. Given that "boosting" means more CPU consumption, I think it'd make more sense to follow such semantics - ie. a descendant cannot have higher boosting than the lowest of its ancestors. Thanks. -- tejun