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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 711B3C0044C for ; Wed, 7 Nov 2018 18:02:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3323A2081D for ; Wed, 7 Nov 2018 18:02:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="OlhO8Q/E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3323A2081D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727944AbeKHDdt (ORCPT ); Wed, 7 Nov 2018 22:33:49 -0500 Received: from mail-io1-f66.google.com ([209.85.166.66]:40398 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726858AbeKHDds (ORCPT ); Wed, 7 Nov 2018 22:33:48 -0500 Received: by mail-io1-f66.google.com with SMTP id a23-v6so12596374iod.7 for ; Wed, 07 Nov 2018 10:02:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Jrf3UjIRgZLX0qSwTeavz5cyKeknX1VS1z8QHfJ1ezc=; b=OlhO8Q/Ebfhe0wMnlZWTMX21Gx9/60heaWyJ8gHbSm/Wvylo3LerhWJqNlZSFrXz9o YovUaiGZ8k7fslADO36kJ9PKfpz1tJzdP9kbgYAo0YYzCfiXAMJ461z1irHHeSm0Tn9c YnbVQv+b/cB+IzfJiwH4Ioxzavx2UZxuP/sVY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Jrf3UjIRgZLX0qSwTeavz5cyKeknX1VS1z8QHfJ1ezc=; b=EhZ3jsRwHnuhxVdVCifVtA6ltzMrd6ybubBqXzYEHP6EihEpbrOE+LjBC6pa/AFFGJ inDtwIyGwPoAWjrEQoACQx7El2Pb21DMjW5rAIhspOJXbJRKKlYo/aFzDmLr+EXN8mdD JAY1BrAKH02XKHs3PKJTKQhZCi+hwO8A+63+jy3qLVH0x+af0D8QNdhmoz0dPhYFDiHo DUgTGFnYf97IQKixJTYUR3EasWSEybXcFIRjwoGyXxmSQDujJiGGdIjDFotGrI0gTXuw KNjpX6zXjapSEcvntuhMjYCv4CYIF5gxd0w1xvp+Fo3g+td8jMTlWGFO4mO3Sn+qWnBD mnPA== X-Gm-Message-State: AGRZ1gJ336R7/+Q/K4FUvIs0bW5AQyN8BFZG4vz6EnCdutn+cNEdRsOE O087kiirnd4GI6YgUbjWCirEe0QmVc3dd0KUa+fbew== X-Google-Smtp-Source: AJdET5euT1cIOuPJd5bfxbVcv92PYM0xDzfldWdV3oz2/YxPMo/tk8DG6zZkc39rDn9sUa1ArJabWCw46Typ5VpGb5I= X-Received: by 2002:a6b:244:: with SMTP id 65-v6mr986578ioc.183.1541613737918; Wed, 07 Nov 2018 10:02:17 -0800 (PST) MIME-Version: 1.0 References: <20181016101513.26919-1-quentin.perret@arm.com> <20181016101513.26919-4-quentin.perret@arm.com> <20181107170213.yapun7nk5rrjdf55@queper01-lin> In-Reply-To: <20181107170213.yapun7nk5rrjdf55@queper01-lin> From: Vincent Guittot Date: Wed, 7 Nov 2018 19:02:06 +0100 Message-ID: Subject: Re: [PATCH v8 03/15] PM: Introduce an Energy Model management framework To: Quentin Perret Cc: Peter Zijlstra , "Rafael J. Wysocki" , linux-kernel , "open list:THERMAL" , "gregkh@linuxfoundation.org" , Ingo Molnar , Dietmar Eggemann , Morten Rasmussen , Chris Redpath , Patrick Bellasi , Valentin Schneider , Thara Gopinath , viresh kumar , Todd Kjos , Joel Fernandes , "Cc: Steve Muckle" , adharmap@codeaurora.org, Saravana Kannan , pkondeti@codeaurora.org, Juri Lelli , Eduardo Valentin , Srinivas Pandruvada , currojerez@riseup.net, Javi Merino Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 Nov 2018 at 18:02, Quentin Perret wrote: > > Hi Vincent, > > On Wednesday 07 Nov 2018 at 17:32:32 (+0100), Vincent Guittot wrote: > > Hi Quentin, > > > > On Tue, 16 Oct 2018 at 12:15, Quentin Perret wrote: > > > > > > > > + > > > +/** > > > + * em_pd_energy() - Estimates the energy consumed by the CPUs of a perf. domain > > > + * @pd : performance domain for which energy has to be estimated > > > + * @max_util : highest utilization among CPUs of the domain > > > + * @sum_util : sum of the utilization of all CPUs in the domain > > > + * > > > + * Return: the sum of the energy consumed by the CPUs of the domain assuming > > > + * a capacity state satisfying the max utilization of the domain. > > > + */ > > > +static inline unsigned long em_pd_energy(struct em_perf_domain *pd, > > > + unsigned long max_util, unsigned long sum_util) > > > +{ > > > + unsigned long freq, scale_cpu; > > > + struct em_cap_state *cs; > > > + int i, cpu; > > > + > > > + /* > > > + * In order to predict the capacity state, map the utilization of the > > > + * most utilized CPU of the performance domain to a requested frequency, > > > + * like schedutil. > > > + */ > > > + cpu = cpumask_first(to_cpumask(pd->cpus)); > > > + scale_cpu = arch_scale_cpu_capacity(NULL, cpu); > > > + cs = &pd->table[pd->nr_cap_states - 1]; > > > + freq = map_util_freq(max_util, cs->frequency, scale_cpu); > > > + > > > + /* > > > + * Find the lowest capacity state of the Energy Model above the > > > + * requested frequency. > > > + */ > > > + for (i = 0; i < pd->nr_cap_states; i++) { > > > + cs = &pd->table[i]; > > > + if (cs->frequency >= freq) > > > + break; > > > + } > > > + > > > + /* > > > + * The capacity of a CPU in the domain at that capacity state (cs) > > > + * can be computed as: > > > + * > > > + * cs->freq * scale_cpu > > > + * cs->cap = -------------------- (1) > > > + * cpu_max_freq > > > + * > > > + * So, ignoring the costs of idle states (which are not available in > > > + * the EM), the energy consumed by this CPU at that capacity state is > > > + * estimated as: > > > + * > > > + * cs->power * cpu_util > > > + * cpu_nrg = -------------------- (2) > > > + * cs->cap > > > + * > > > + * since 'cpu_util / cs->cap' represents its percentage of busy time. > > > + * > > > + * NOTE: Although the result of this computation actually is in > > > + * units of power, it can be manipulated as an energy value > > > + * over a scheduling period, since it is assumed to be > > > + * constant during that interval. > > > + * > > > + * By injecting (1) in (2), 'cpu_nrg' can be re-expressed as a product > > > + * of two terms: > > > + * > > > + * cs->power * cpu_max_freq cpu_util > > > + * cpu_nrg = ------------------------ * --------- (3) > > > + * cs->freq scale_cpu > > > + * > > > + * The first term is static, and is stored in the em_cap_state struct > > > + * as 'cs->cost'. > > > + * > > > + * Since all CPUs of the domain have the same micro-architecture, they > > > + * share the same 'cs->cost', and the same CPU capacity. Hence, the > > > + * total energy of the domain (which is the simple sum of the energy of > > > + * all of its CPUs) can be factorized as: > > > + * > > > + * cs->cost * \Sum cpu_util > > > + * pd_nrg = ------------------------ (4) > > > + * scale_cpu > > > + */ > > > + return cs->cost * sum_util / scale_cpu; > > > > Why do you need to keep scale_cpu outside the cs->cost ? do you expect > > arch_scale_cpu_capacity() to change at runtime ? > > Unfortunately yes, it can. It'll change at least during boot on arm64, > for example (see drivers/base/arch_topology.c). And also, userspace can > actually set that value via sysfs ... yes. I had this in mind too but we are also rebuilding sched_domain in this case and thought that everything could be changed at the same time > > > If the returned value of arch_scale_cpu_capacity() changes, we will > > have to rebuild several others things and we can include the update of > > cs->cost > > Yeah, that was the original approach I had actually. Some of the older > versions of this patch set were doing just that. The only issue is that, > in order to make the cs->cost updatable are run time, you need to > introduce some level of protection around that data structure (RCU or > something). And that would make it a bit harder for IPA (for example) to > access the data -- it doesn't need any kind of RCU to access it's EM at > the moment. > > We can probably do something a bit smarter and introduce RCU protection > only for the 'cost' field or something, but I was hoping that we could > keep things simple for now and do that kind of small optimization a bit > later :-) Thanks for the explanation > > Thanks, > Quentin