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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 4EB5DC04AAF for ; Thu, 16 May 2019 13:06:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BD0A20833 for ; Thu, 16 May 2019 13:06:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726623AbfEPNGM (ORCPT ); Thu, 16 May 2019 09:06:12 -0400 Received: from foss.arm.com ([217.140.101.70]:45086 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726618AbfEPNGM (ORCPT ); Thu, 16 May 2019 09:06:12 -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 1668D1715; Thu, 16 May 2019 06:06:12 -0700 (PDT) Received: from [10.1.195.43] (e107049-lin.cambridge.arm.com [10.1.195.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 865633F703; Thu, 16 May 2019 06:06:10 -0700 (PDT) Subject: Re: [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq() To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, quentin.perret@arm.com, dietmar.eggemann@arm.com, rjw@rjwysocki.net, Viresh Kumar References: <20190508174301.4828-1-douglas.raillard@arm.com> <20190508174301.4828-2-douglas.raillard@arm.com> <20190516124200.opxczohjelhvrzmo@e110439-lin> From: Douglas Raillard Organization: ARM Message-ID: <046bfab7-bf28-bbfe-2bff-09881d537fb1@arm.com> Date: Thu, 16 May 2019 14:06:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190516124200.opxczohjelhvrzmo@e110439-lin> Content-Type: text/plain; charset="UTF-8"; format="flowed" Content-Language: en-GB-large Content-Transfer-Encoding: 7bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Message-ID: <20190516130608.yGeCuFC3T9i2BNlpuLV9-grUHaZOnKc8Sv1TIyKaGUQ@z> Hi Patrick, On 5/16/19 1:42 PM, Patrick Bellasi wrote: > On 08-May 18:42, douglas.raillard@arm.com wrote: >> From: Douglas RAILLARD >> >> em_pd_get_higher_freq() returns a frequency greater or equal to the >> provided one while taking into account a given cost margin. It also >> skips inefficient OPPs that have a higher cost than another one with a >> higher frequency. > > It's worth to add a small description and definition of what we mean by > "OPP efficiency". Despite being just an RFC, it could help to better > understand what we are after. Right, here efficiency=capacity/power. > > [...] > >> +/** + * em_pd_get_higher_freq() - Get the highest frequency that >> does not exceed the >> + * given cost margin compared to min_freq >> + * @pd : performance domain for which this must be done >> + * @min_freq : minimum frequency to return >> + * @cost_margin : allowed margin compared to min_freq, as a per-1024 value. > ^^^^^^^^ > here... > >> + * >> + * Return: the chosen frequency, guaranteed to be at least as high as min_freq. >> + */ >> +static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd, >> + unsigned long min_freq, unsigned long cost_margin) >> +{ >> + unsigned long max_cost = 0; >> + struct em_cap_state *cs; >> + int i; >> + >> + if (!pd) >> + return min_freq; >> + >> + /* Compute the maximum allowed cost */ >> + for (i = 0; i < pd->nr_cap_states; i++) { >> + cs = &pd->table[i]; >> + if (cs->frequency >= min_freq) { >> + max_cost = cs->cost + (cs->cost * cost_margin) / 1024; > ^^^^ > ... end here we should probably better use SCHED_CAPACITY_SCALE > instead of hard-coding in values, isn't it? "cs->cost*cost_margin/1024" is not a capacity, it's a cost as defined here: https://elixir.bootlin.com/linux/latest/source/include/linux/energy_model.h#L17 Actually, it's in milliwatts, but it's not better the better way to look at it to understand it IMHO. The margin is expressed as a "per-1024" value just like we use percents' in everyday life, so it has no unit. If we want to avoid hard-coded values here, I can introduce an ENERGY_COST_MARGIN_SCALE macro. >> + break; >> + } >> + } >> + > > [...] > > Best, > Patrick Thanks, Douglas