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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 97AE4C4361B for ; Fri, 11 Dec 2020 11:32:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B9E723F2A for ; Fri, 11 Dec 2020 11:32:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394872AbgLKLcL (ORCPT ); Fri, 11 Dec 2020 06:32:11 -0500 Received: from foss.arm.com ([217.140.110.172]:51326 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394860AbgLKLbc (ORCPT ); Fri, 11 Dec 2020 06:31:32 -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 8BECA31B; Fri, 11 Dec 2020 03:30:46 -0800 (PST) Received: from [192.168.178.2] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 663F93F68F; Fri, 11 Dec 2020 03:30:43 -0800 (PST) Subject: Re: [PATCH] fair/util_est: Separate util_est_dequeue() for cfs_rq_util_change To: Xuewen Yan , patrick.bellasi@arm.com, vincent.guittot@linaro.org, peterz@infradead.org Cc: mingo@redhat.com, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, Xuewen.Yan@unisoc.com, xuewyan@foxmail.com References: <1607510656-22990-1-git-send-email-xuewen.yan@unisoc.com> From: Dietmar Eggemann Message-ID: <2edefcc7-ccea-5665-728e-5b86ac413629@arm.com> Date: Fri, 11 Dec 2020 12:30:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <1607510656-22990-1-git-send-email-xuewen.yan@unisoc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Yan, On 09/12/2020 11:44, Xuewen Yan wrote: > when a task dequeued, it will update it's util, and cfs_rq_util_change > would check rq's util, if the cfs_rq->avg.util_est.enqueued is bigger > than cfs_rq->avg.util_avg, but because the cfs_rq->avg.util_est.enqueued > didn't be decreased, this would cause bigger cfs_rq_util by mistake, > as a result, cfs_rq_util_change may change freq unreasonablely. > > separate the util_est_dequeue() into util_est_dequeue() and > util_est_update(), and dequeue the _task_util_est(p) before update util. The issue is that sugov_update_[shared\|single] -> sugov_get_util() -> cpu_util_cfs() operates on an old cfs_rq->avg.util_est.enqueued value? cpu_util_cfs() if (sched_feat(UTIL_EST)) util = max_t(util, READ_ONCE(rq->cfs.avg.util_est.enqueued)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ dequeue_task_fair() (w/ your patch, moving (1) before (2)) /* (1) update cfs_rq->avg.util_est.enqueued */ util_est_dequeue() /* (2) potential p->se.avg.util_avg update */ /* 2 for loops */ for_each_sched_entity() /* this can only lead to a freq change for a root cfs_rq */ (dequeue_entity() ->) update_load_avg() -> cfs_rq_util_change() -> cpufreq_update_util() ->...-> sugov_update_[shared\|single] /* (3) potential update p->se.avg.util_est */ util_est_update() We do need (3) after (2) because of: util_est_update() ... ue.enqueued = (task_util(p) | UTIL_AVG_UNCHANGED); task_util ... ^^^^^^^^^^^^^ p->se.avg.util_avg Did I get this right? [...]