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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 ED31AFA372A for ; Thu, 17 Oct 2019 09:59:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9B2421D7D for ; Thu, 17 Oct 2019 09:59:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405778AbfJQJ7H (ORCPT ); Thu, 17 Oct 2019 05:59:07 -0400 Received: from [217.140.110.172] ([217.140.110.172]:37694 "EHLO foss.arm.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S2405688AbfJQJ7G (ORCPT ); Thu, 17 Oct 2019 05:59:06 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 52E201B4B; Thu, 17 Oct 2019 02:58:40 -0700 (PDT) Received: from [192.168.0.9] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 838423F718; Thu, 17 Oct 2019 02:58:38 -0700 (PDT) Subject: Re: [RFC PATCH v3 1/6] PM: Introduce em_pd_get_higher_freq() To: Douglas RAILLARD , linux-kernel@vger.kernel.org Cc: linux-pm@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, rjw@rjwysocki.net, viresh.kumar@linaro.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, qperret@qperret.net, patrick.bellasi@matbug.net, dh.han@samsung.com References: <20191011134500.235736-1-douglas.raillard@arm.com> <20191011134500.235736-2-douglas.raillard@arm.com> From: Dietmar Eggemann Message-ID: <5aa79534-7059-09e7-00b8-752f6699f9d4@arm.com> Date: Thu, 17 Oct 2019 11:58:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191011134500.235736-2-douglas.raillard@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 11/10/2019 15:44, Douglas RAILLARD wrote: [...] > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h > index d249b88a4d5a..dd6a35f099ea 100644 > --- a/include/linux/energy_model.h > +++ b/include/linux/energy_model.h > @@ -159,6 +159,53 @@ static inline int em_pd_nr_cap_states(struct em_perf_domain *pd) > return pd->nr_cap_states; > } > > +#define EM_COST_MARGIN_SCALE 1024U > + > +/** > + * 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, on the > + * EM_COST_MARGIN_SCALE scale. > + * > + * 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) / EM_COST_MARGIN_SCALE; Maybe you could mention in the header that this is the place where the algorithm could be tuned. (even though it doesn't offer any tuning interface, which is a good thing). > + break; > + } > + } > + > + /* Find the highest frequency that will not exceed the cost margin */ > + for (i = pd->nr_cap_states-1; i >= 0; i--) { > + cs = &pd->table[i]; > + if (cs->cost <= max_cost) > + return cs->frequency; > + } > + > + /* > + * We should normally never reach here, unless min_freq was higher than > + * the highest available frequency, which is not expected to happen. > + */ Maybe add a WARN_ONCE(1, "foobar"); here to indicate this unlikely event (CPUfreq and EM framwork out of sync)? [...]