Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935173AbcCPSgM (ORCPT ); Wed, 16 Mar 2016 14:36:12 -0400 Received: from casper.infradead.org ([85.118.1.10]:38642 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934328AbcCPSgK (ORCPT ); Wed, 16 Mar 2016 14:36:10 -0400 Date: Wed, 16 Mar 2016 19:36:07 +0100 From: Peter Zijlstra To: Steve Muckle Cc: Michael Turquette , rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Juri.Lelli@arm.com, morten.rasmussen@arm.com, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, Michael Turquette Subject: Re: [PATCH 6/8] cpufreq/schedutil: sum per-sched class utilization Message-ID: <20160316183607.GI6344@twins.programming.kicks-ass.net> References: <1457932932-28444-1-git-send-email-mturquette+renesas@baylibre.com> <1457932932-28444-7-git-send-email-mturquette+renesas@baylibre.com> <20160315212926.GG6344@twins.programming.kicks-ass.net> <20160315220951.30639.12872@quark.deferred.io> <20160316073850.GO6344@twins.programming.kicks-ass.net> <56E9A3FD.9050309@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56E9A3FD.9050309@linaro.org> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1083 Lines: 24 On Wed, Mar 16, 2016 at 11:20:45AM -0700, Steve Muckle wrote: > On 03/16/2016 12:38 AM, Peter Zijlstra wrote: > > Somewhere in the giant discussions I mentioned that we should be looking > > at a CPPC like interface and pass {min,max} tuples to the cpufreq > > selection thingy. > > > > In that same discussion I also mentioned that we must compute min as the > > hard dl reservation, but that for max we can actually use the avg dl + > > avg rt + avg cfs. > > > > That way there is far more room for selecting a sensible frequency. > > Doesn't the above min/max policy mean that the platform will likely > underserve the task load? If avg dl+rt+cfs represents our best estimate > of the work to be done, I would think that should be the min. Can't be the min, avg_dl might (and typically will be) must lower than the worst case utilization estimates. However if we use that as our min, peaks in DL utilization will not complete, because we run at too low a frequency. Therefore, the min must be given by our worst case utilization reservation, not by the actual avg consumed.