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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 0809EC4321A for ; Fri, 28 Jun 2019 12:38:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B93CF20644 for ; Fri, 28 Jun 2019 12:38:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="JmMzddkU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727182AbfF1MiS (ORCPT ); Fri, 28 Jun 2019 08:38:18 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42600 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726675AbfF1MiS (ORCPT ); Fri, 28 Jun 2019 08:38:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=FojrDMPPmqbimK77TYezVK4kRVrgRTN5l96O/2ImwMI=; b=JmMzddkUbEhnT2ek+gUHcvRWv 5t1OvaVQKIG9pjj6czOKMGxqFBa7R+IFEDTXCE3RqUuUi6hahTdkmrLmWxZ7ruPre7DCTY+VKOzWw IzF/VyJFtMqho2QRWVnSSUsAuIJkfYLm8FrDfghiGPWUz29C80lOubuS/9V2lmuAsP6vy2vemIenm oepwbbKxoEktwhjlyvXolby5NKaSlo+uHUWdt4yxgMhCMYudzl9Qu4dx81QMA6skh6GltsfgkWVKr fjbSqxoDBI05scDRTX2arf6pWFcQr0qg6xLdOJUzVV5SQo3EgPlFbWTC/yun1Oj71RygB8jMcaSVt A/wxz8WoA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hgq8h-0000WE-Ka; Fri, 28 Jun 2019 12:38:03 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6BB47201F4619; Fri, 28 Jun 2019 14:38:00 +0200 (CEST) Date: Fri, 28 Jun 2019 14:38:00 +0200 From: Peter Zijlstra To: Patrick Bellasi Cc: Vincent Guittot , linux-kernel , Ingo Molnar , "Rafael J . Wysocki" , Viresh Kumar , Douglas Raillard , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli Subject: Re: [PATCH] sched/fair: util_est: fast ramp-up EWMA on utilization increases Message-ID: <20190628123800.GS3419@hirez.programming.kicks-ass.net> References: <20190620150555.15717-1-patrick.bellasi@arm.com> <20190628100751.lpcwsouacsi2swkm@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190628100751.lpcwsouacsi2swkm@e110439-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28, 2019 at 11:08:14AM +0100, Patrick Bellasi wrote: > On 26-Jun 13:40, Vincent Guittot wrote: > > Hi Patrick, > > > > On Thu, 20 Jun 2019 at 17:06, Patrick Bellasi wrote: > > > > > > The estimated utilization for a task is currently defined based on: > > > - enqueued: the utilization value at the end of the last activation > > > - ewma: an exponential moving average which samples are the enqueued values > > > > > > According to this definition, when a task suddenly change it's bandwidth > > > requirements from small to big, the EWMA will need to collect multiple > > > samples before converging up to track the new big utilization. > > > > > > Moreover, after the PELT scale invariance update [1], in the above scenario we > > > can see that the utilization of the task has a significant drop from the first > > > big activation to the following one. That's implied by the new "time-scaling" > > > > Could you give us more details about this? I'm not sure to understand > > what changes between the 1st big activation and the following one ? > > We are after a solution for the problem Douglas Raillard discussed at > OSPM, specifically the "Task util drop after 1st idle" highlighted in > slide 6 of his presentation: > > http://retis.sssup.it/ospm-summit/Downloads/02_05-Douglas_Raillard-How_can_we_make_schedutil_even_more_effective.pdf > So I see the problem, and I don't hate the patch, but I'm still struggling to understand how exactly it related to the time-scaling stuff. Afaict the fundamental problem here is layering two averages. The second (EWMA in our case) will always lag/delay the input of the first (PELT). The time-scaling thing might make matters worse, because that helps PELT ramp up faster, but that is not the primary issue. Or am I missing something?