Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755311AbcCPMpX (ORCPT ); Wed, 16 Mar 2016 08:45:23 -0400 Received: from mail-lb0-f193.google.com ([209.85.217.193]:36160 "EHLO mail-lb0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755109AbcCPMpP (ORCPT ); Wed, 16 Mar 2016 08:45:15 -0400 MIME-Version: 1.0 In-Reply-To: <20160316080503.GS6344@twins.programming.kicks-ass.net> References: <1457932932-28444-1-git-send-email-mturquette+renesas@baylibre.com> <1457932932-28444-5-git-send-email-mturquette+renesas@baylibre.com> <20160315212047.GE6344@twins.programming.kicks-ass.net> <20160315214043.30639.75507@quark.deferred.io> <20160315214821.GM6344@twins.programming.kicks-ass.net> <20160315223701.30639.43127@quark.deferred.io> <56E8D4D9.1060202@linaro.org> <20160316080503.GS6344@twins.programming.kicks-ass.net> Date: Wed, 16 Mar 2016 13:45:12 +0100 X-Google-Sender-Auth: Xc78rfb05GMRktuPfvZo4pWd-9A Message-ID: Subject: Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable From: "Rafael J. Wysocki" To: Peter Zijlstra Cc: Steve Muckle , Michael Turquette , "Rafael J. Wysocki" , Linux Kernel Mailing List , "linux-pm@vger.kernel.org" , Juri Lelli , Morten Rasmussen , Dietmar Eggemann , Vincent Guittot , Michael Turquette , Patrick Bellasi Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1250 Lines: 25 On Wed, Mar 16, 2016 at 9:05 AM, Peter Zijlstra wrote: > On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote: >> > Then again, maybe this knob will be part of the mythical >> > power-vs-performance slider? >> >> Patrick Bellasi's schedtune series [0] (which I think is the referenced >> mythical slider) aims to provide a more sophisticated interface for >> tuning scheduler-driven frequency selection. In addition to a global >> boost value it includes a cgroup controller as well for per-task tuning. >> >> I would definitely expect the margin/boost value to be modified at >> runtime, for example if the battery is running low, or the user wants >> 100% performance for a while, or the userspace framework wants to >> temporarily tailor the performance level for a particular set of tasks, etc. > > OK, so how about we start with it as a debug knob, and once we have > experience and feel like it is indeed a useful runtime knob, we upgrade > it to ABI. > > The problem with starting out as ABI is that its hard to take away > again. Agreed, plus it is quite hard to get ABI right from the outset. Even if we decide on a sysfs knob, it still is unclear what exactly should be represented by it in what units etc.