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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E99F2C43441 for ; Wed, 28 Nov 2018 11:53:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9407520989 for ; Wed, 28 Nov 2018 11:53:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9407520989 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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 S1728154AbeK1WzF (ORCPT ); Wed, 28 Nov 2018 17:55:05 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:36852 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727585AbeK1WzF (ORCPT ); Wed, 28 Nov 2018 17:55:05 -0500 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 795773650; Wed, 28 Nov 2018 03:53:41 -0800 (PST) Received: from e110439-lin (e110439-lin.cambridge.arm.com [10.1.194.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 413823F59C; Wed, 28 Nov 2018 03:53:39 -0800 (PST) Date: Wed, 28 Nov 2018 11:53:36 +0000 From: Patrick Bellasi To: Peter Zijlstra Cc: Vincent Guittot , Ingo Molnar , linux-kernel , "Rafael J. Wysocki" , Dietmar Eggemann , Morten Rasmussen , Paul Turner , Ben Segall , Thara Gopinath , pkondeti@codeaurora.org, Quentin Perret , Srinivas Pandruvada Subject: Re: [PATCH v7 2/2] sched/fair: update scale invariance of PELT Message-ID: <20181128115336.GB23094@e110439-lin> References: <1542711308-25256-1-git-send-email-vincent.guittot@linaro.org> <1542711308-25256-3-git-send-email-vincent.guittot@linaro.org> <20181128100241.GA2131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181128100241.GA2131@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28-Nov 11:02, Peter Zijlstra wrote: > On Wed, Nov 28, 2018 at 10:54:13AM +0100, Vincent Guittot wrote: > > > Is there anything else that I should do for these patches ? > > IIRC, Morten mention they break util_est; Patrick was going to explain. I guess the problem is that, once we cross the current capacity, strictly speaking util_avg does not represent anymore a utilization. With the new signal this could happen and we end up storing estimated utilization samples which will overestimate the task requirements. We will have a spike in estimated utilization at next wakeup, since we use MAX(util_avg@dequeue_time, ewma). Potentially we also inflate the EWMA in case we collect multiple samples above the current capacity. So, a possible fix could be to avoid storing util_est samples if we end up with a utilization above the current capacity. Something like: ----8<--- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ac855b2f4774..93e0cf5d8a76 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3661,6 +3661,10 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep) if (!task_sleep) return; + /* Skip samples which do not represent an actual utilization */ + if (unlikely(task_util(p) > capacity_of(task_cpu(p)))) + return; + /* * If the PELT values haven't changed since enqueue time, * skip the util_est update. ---8<--- Could that work ? Maybe using a new utility function to wrap the new check. -- #include Patrick Bellasi