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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 E761EC11D2F for ; Mon, 24 Feb 2020 15:57:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C45BC20828 for ; Mon, 24 Feb 2020 15:57:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727959AbgBXP5k (ORCPT ); Mon, 24 Feb 2020 10:57:40 -0500 Received: from foss.arm.com ([217.140.110.172]:39180 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727693AbgBXP5k (ORCPT ); Mon, 24 Feb 2020 10:57:40 -0500 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 68E031FB; Mon, 24 Feb 2020 07:57:39 -0800 (PST) Received: from [10.1.195.59] (ifrit.cambridge.arm.com [10.1.195.59]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E68813F703; Mon, 24 Feb 2020 07:57:37 -0800 (PST) Subject: Re: [PATCH v3 4/5] sched/pelt: Add a new runnable average signal To: Vincent Guittot Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel , Phil Auld , Parth Shah , Hillf Danton References: <20200214152729.6059-5-vincent.guittot@linaro.org> <20200219125513.8953-1-vincent.guittot@linaro.org> <9fe822fc-c311-2b97-ae14-b9269dd99f1e@arm.com> From: Valentin Schneider Message-ID: Date: Mon, 24 Feb 2020 15:57:36 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I somehow lost track of that email, sorry for the delayed response. On 2/21/20 8:56 AM, Vincent Guittot wrote: > On Thu, 20 Feb 2020 at 17:11, Valentin Schneider > wrote: >> >> On 20/02/2020 14:36, Vincent Guittot wrote: >>> I agree that setting by default to SCHED_CAPACITY_SCALE is too much >>> for little core. >>> The problem for little core can be fixed by using the cpu capacity instead >>> >> >> So that's indeed better for big.LITTLE & co. Any reason however for not >> aligning with the initialization of util_avg ? > > The runnable_avg is the unweighted version of the load_avg so they > should both be sync at init and SCHED_CAPACITY_SCALE is in fact the > right value. Using cpu_scale is the same for smp and big core so we > can use it instead. > > Then, the initial value of util_avg has never reflected some kind of > realistic value for the utilization of a new task, especially if those > tasks will become big ones. Runnable_avg now balances this effect to > say that we don't know what will be the behavior of the new task, > which might end up using all spare capacity although current > utilization is low and CPU is not "fully used". I'd argue that the init values we pick for either runnable_avg or util_avg are both equally bogus. > In fact, this is > exactly the purpose of runnable: highlight that there is maybe no > spare capacity even if CPU's utilization is low because of external > event like task migration or having new tasks with most probably wrong > utilization. > > That being said, there is a bigger problem with the current version of > this patch, which is that I forgot to use runnable in > update_sg_wakeup_stats(). I have a patch that fixes this problem. > > Also, I have tested both proposals with hackbench on my octo cores and > using cpu_scale gives slightly better results than util_avg, which > probably reflects the case I mentioned above. > > grp cpu_scale util_avg improvement > 1 1,191(+/-0.77 %) 1,204(+/-1.16 %) -1.07 % > 4 1,147(+/-1.14 %) 1,195(+/-0.52 %) -4.21 % > 8 1,112(+/-1,52 %) 1,124(+/-1,45 %) -1.12 % > 16 1,163(+/-1.72 %) 1,169(+/-1.58 %) -0,45 % > Interesting, thanks for providing the numbers. I'd be curious to figure out where the difference really stems from, but in the meantime consider me convinced ;)