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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 184D3C2BA1A for ; Fri, 24 Apr 2020 09:06:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F078A20724 for ; Fri, 24 Apr 2020 09:06:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726813AbgDXJGm (ORCPT ); Fri, 24 Apr 2020 05:06:42 -0400 Received: from foss.arm.com ([217.140.110.172]:57754 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726699AbgDXJGl (ORCPT ); Fri, 24 Apr 2020 05:06:41 -0400 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 192191FB; Fri, 24 Apr 2020 02:06:41 -0700 (PDT) Received: from [192.168.0.7] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 471D63F73D; Fri, 24 Apr 2020 02:06:39 -0700 (PDT) Subject: Re: [PATCH] sched/pelt: sync util/runnable_sum with PELT window when propagating To: Vincent Guittot Cc: Peter Zijlstra , Ingo Molnar , Juri Lelli , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel References: <20200422151401.9147-1-vincent.guittot@linaro.org> <20200423192930.GY2483@worktop.programming.kicks-ass.net> <206b1f00-bb96-5e7f-f80a-b10cd88c8a71@arm.com> From: Dietmar Eggemann Message-ID: Date: Fri, 24 Apr 2020 11:06:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 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 On 24/04/2020 10:54, Vincent Guittot wrote: > On Fri, 24 Apr 2020 at 10:41, Dietmar Eggemann wrote: >> >> On 24/04/2020 09:37, Vincent Guittot wrote: >>> On Thu, 23 Apr 2020 at 21:29, Peter Zijlstra wrote: >>>> >>>> On Wed, Apr 22, 2020 at 05:14:01PM +0200, Vincent Guittot wrote: [...] >>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>>> index 02f323b85b6d..ca6aa89c88f2 100644 >>>>> --- a/kernel/sched/fair.c >>>>> +++ b/kernel/sched/fair.c >>>>> @@ -3441,52 +3441,38 @@ static inline void >>>>> update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq) >>>>> { >>>>> long delta = gcfs_rq->avg.util_avg - se->avg.util_avg; >>>>> + u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib; >>>>> >>>>> /* Nothing to update */ >>>>> if (!delta) >>>>> return; >>>>> >>>>> - /* >>>>> - * The relation between sum and avg is: >>>>> - * >>>>> - * LOAD_AVG_MAX - 1024 + sa->period_contrib >>>>> - * >>>>> - * however, the PELT windows are not aligned between grq and gse. >>>>> - */ >>>> >>>> Instead of deleting this, could we perhaps extend it? >>> >>> In fact, this is not the only place in fair.c that uses this rule to >>> align _avg and _sum but others don't have any special comment. >>> >>> I can add a more detailed description of this relation for >>> ___update_load_avg() in pelt.c and make a ref to this in all places in >>> fair.c that use this rule which are : >>> - update_tg_cfs_util >>> - update_tg_cfs_runnable >>> - update_cfs_rq_load_avg >>> - attach_entity_load_avg >>> - reweight_entity >> >> But IMHO the >> >> "* however, the PELT windows are not aligned between grq and gse." >> >> should only apply to update_tg_cfs_util() and update_tg_cfs_runnable(). >> And attach_entity_load_avg() (for cfs_rq and se). >> >> They seem to be special since we derive divider from a cfs_rq PELT value >> and use it for a se PELT value. > > hmmm... There is nothing special here. > > When se is attached to cfs_rq, they both have the same divider because > they use the same clock. That's true. But exactly this might deserve this comment. Otherwise people might wonder why you can do a u32 divider = LOAD_AVG_MAX - 1024 + *cfs_rq*->avg.period_contrib; and use it for instance in: *se*->avg.util_sum = se->avg.util_avg * divider; In update_cfs_rq_load_avg() and reweight_entity() we derive 'divider' from the same 'sched_avg' we use it on later. u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib; sub_positive(&sa->load_sum, r * divider); [...]