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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 076FFC07E9B for ; Wed, 7 Jul 2021 10:11:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC1D0619A5 for ; Wed, 7 Jul 2021 10:11:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231236AbhGGKOW (ORCPT ); Wed, 7 Jul 2021 06:14:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39264 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229949AbhGGKOV (ORCPT ); Wed, 7 Jul 2021 06:14:21 -0400 Received: from mail-lj1-x230.google.com (mail-lj1-x230.google.com [IPv6:2a00:1450:4864:20::230]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27E7BC06175F for ; Wed, 7 Jul 2021 03:11:41 -0700 (PDT) Received: by mail-lj1-x230.google.com with SMTP id u25so1970593ljj.11 for ; Wed, 07 Jul 2021 03:11:41 -0700 (PDT) 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=ZuEZ3jVwrZtFCL3Zmrw9iRdslo4LWzfGrwGrKzCDfNM=; b=AAdlg8dWvWETI7yrZa9aa6Hdro1l4MMrDxlZvCQPrdjBC6Lu8L5XpdJ8kF5j24k5y4 Y5k9ZiS9AhCI3B+YaLG3W0oohu90Vkdido2p8x/H1GJAMDXVMdk+eqpNknpqulTNZPUp iFDT45h0qeyqGVewt3oXb7mNoi8U5l9D/xqB6N5ZUc3F1WdoLxBqkq31e+I4LvDmv9P5 YtYG4rsvQm4ySrLFLX7oBWpYMaTKeYZFWRs4c1lt2bnfiAgW1TjOKhUlzQ3Hr7Nloat2 dG+EDQJWtWEuOkhjrWP3stTaGex5ZK7ShYH+yo5peV1Gp4O3/YemPXWuW/xCpsiIvp6f RHqQ== 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=ZuEZ3jVwrZtFCL3Zmrw9iRdslo4LWzfGrwGrKzCDfNM=; b=SHNaTMxg1FJlPXQQGyeDqm8/dGpCIxNJ37wp1eNta4QitXY39bT/TNjG19VghglfEv q/NWkLTIw8ecrIxivHYduV9Nw7z6VKyTMACNiw4+6jxzxyjLAjlfCH3ptCd7MCft33kQ CHWi7Ehi5FYnq0OvPXbNjMuO6r4E6ne+g3eGbhGDLRmhRt0I33pPrULQ3TEXE5AXekGq I/znAmG9uf46XsiDdcdxQG063pqm6C4KCmEBbgiDvEZai3Xzq+NyIK21CrPyw0oe2kD4 VxjNp8/3arPs09aXU9QSzkCS24fLer/vaV5fVCPLJwhb4HoWEFEGYqcVXK3FBpm+SXUb 0nrQ== X-Gm-Message-State: AOAM5326WW1c3ctI0+M353ORmrXv5Px6XAPxqwdZ8YUBNRk5HyfX8J2n k91SWC3l/9mKyD0JXeizMWgn5LQaMcWyRl7coJ8SOw== X-Google-Smtp-Source: ABdhPJzgZG6YjG/0gLEf7Rrqwsbi9ls6vUnvFowYrhuar9Mwt4w6AamkBtUmy3LIlciesWPf1pZWoMLm9/LjXjMn0q4= X-Received: by 2002:a2e:8941:: with SMTP id b1mr19097509ljk.284.1625652699360; Wed, 07 Jul 2021 03:11:39 -0700 (PDT) MIME-Version: 1.0 References: <20210625152603.25960-1-lukasz.luba@arm.com> <20210625152603.25960-2-lukasz.luba@arm.com> <2f43b211-da86-9d48-4e41-1c63359865bb@arm.com> <297df159-1681-f0a7-843d-f34d86e51d4c@arm.com> <27916860-33b1-f0a0-acff-4722a733c81b@arm.com> In-Reply-To: <27916860-33b1-f0a0-acff-4722a733c81b@arm.com> From: Vincent Guittot Date: Wed, 7 Jul 2021 12:11:28 +0200 Message-ID: Subject: Re: [PATCH 1/3] sched/fair: Prepare variables for increased precision of EAS estimated energy To: Lukasz Luba Cc: linux-kernel , Chris Redpath , Dietmar Eggemann , Morten Rasmussen , Quentin Perret , "open list:THERMAL" , Peter Zijlstra , "Rafael J. Wysocki" , Viresh Kumar , Ingo Molnar , Juri Lelli , Steven Rostedt , segall@google.com, Mel Gorman , Daniel Bristot de Oliveira , CCj.Yeh@mediatek.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 Jul 2021 at 12:06, Lukasz Luba wrote: > > > > On 7/7/21 10:56 AM, Vincent Guittot wrote: > > On Wed, 7 Jul 2021 at 11:48, Lukasz Luba wrote: > >> > >> > >> > >> On 7/7/21 10:37 AM, Vincent Guittot wrote: > >>> On Wed, 7 Jul 2021 at 10:23, Lukasz Luba wrote: > >>>> > >>>> > >>>> > >>>> On 7/7/21 9:00 AM, Vincent Guittot wrote: > >>>>> On Wed, 7 Jul 2021 at 09:49, Lukasz Luba wrote: > >>>>>> > >>>>>> > >>>>>> > >>>>>> On 7/7/21 8:07 AM, Vincent Guittot wrote: > >>>>>>> On Fri, 25 Jun 2021 at 17:26, Lukasz Luba wrote: > >>>>>>>> > >>>>>>>> The Energy Aware Scheduler (EAS) tries to find best CPU for a waking up > >>>>>>>> task. It probes many possibilities and compares the estimated energy values > >>>>>>>> for different scenarios. For calculating those energy values it relies on > >>>>>>>> Energy Model (EM) data and em_cpu_energy(). The precision which is used in > >>>>>>>> EM data is in milli-Watts (or abstract scale), which sometimes is not > >>>>>>>> sufficient. In some cases it might happen that two CPUs from different > >>>>>>>> Performance Domains (PDs) get the same calculated value for a given task > >>>>>>>> placement, but in more precised scale, they might differ. This rounding > >>>>>>>> error has to be addressed. This patch prepares EAS code for better > >>>>>>>> precision in the coming EM improvements. > >>>>>>> > >>>>>>> Could you explain why 32bits results are not enough and you need to > >>>>>>> move to 64bits ? > >>>>>>> > >>>>>>> Right now the result is in the range [0..2^32[ mW. If you need more > >>>>>>> precision and you want to return uW instead, you will have a result in > >>>>>>> the range [0..4kW[ which seems to be still enough > >>>>>>> > >>>>>> > >>>>>> Currently we have the max value limit for 'power' in EM which is > >>>>>> EM_MAX_POWER 0xffff (64k - 1). We allow to register such big power > >>>>>> values ~64k mW (~64Watts) for an OPP. Then based on 'power' we > >>>>>> pre-calculate 'cost' fields: > >>>>>> cost[i] = power[i] * freq_max / freq[i] > >>>>>> So, for max freq the cost == power. Let's use that in the example. > >>>>>> > >>>>>> Then the em_cpu_energy() calculates as follow: > >>>>>> cost * sum_util / scale_cpu > >>>>>> We are interested in the first part - the value of multiplication. > >>>>> > >>>>> But all these are internal computations of the energy model. At the > >>>>> end, the computed energy that is returned by compute_energy() and > >>>>> em_cpu_energy(), fits in a long > >>>> > >>>> Let's take a look at existing *10000 precision for x CPUs: > >>>> cost * sum_util / scale_cpu = > >>>> (64k *10000) * (x * 800) / 1024 > >>>> which is: > >>>> x * ~500mln > >>>> > >>>> So to be close to overflowing u32 the 'x' has to be > (?=) 8 > >>>> (depends on sum_util). > >>> > >>> Sorry but I don't get your point. > >>> This patch is about the return type of compute_energy() and > >>> em_cpu_energy(). And even if we decide to return uW instead of mW, > >>> there is still a lot of margin. > >>> > >>> It's not because you need u64 for computing intermediate value that > >>> you must returns u64 > >> > >> The example above shows the need of u64 return value for platforms > >> which are: > >> - 32bit > >> - have e.g. 16 CPUs > >> - has big power value e.g. ~64k mW > >> Then let's to the calc: > >> (64k * 10000) * (16 * 800) / 1024 = ~8000mln = ~8bln > > > > so you return a power consumption of 8kW !!! > > > > No. It's in 0.1uW scale, so 800Watts. Which is 16 CPUs * 64Watts Oh! you want 0.1uW precision .... This doesn't seem realistic at all. I'm not even sure that the power model can even reach an accuracy of 1mW > each at max freq and 80% load. > > Max power can be < 64Watts, which is 64k milli-Watts (< EM_MAX_POWER) > 64k mW * 10000 --> is the 0.1uW precision >