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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 0AF02C433B4 for ; Fri, 7 May 2021 13:37:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B401A61019 for ; Fri, 7 May 2021 13:37:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237269AbhEGNiA (ORCPT ); Fri, 7 May 2021 09:38:00 -0400 Received: from foss.arm.com ([217.140.110.172]:59490 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235759AbhEGNh6 (ORCPT ); Fri, 7 May 2021 09:37:58 -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 832D7106F; Fri, 7 May 2021 06:36:58 -0700 (PDT) Received: from [192.168.1.16] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4354F3F718; Fri, 7 May 2021 06:36:56 -0700 (PDT) Subject: Re: [PATCH v2] sched/pelt: Keep UTIL_AVG_UNCHANGED flag in sync when calculating last_enqueued_diff To: Vincent Donnefort , Xuewen Yan Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, zhang.lyra@gmail.com, xuewyan@foxmail.com References: <20210507112031.23073-1-xuewen.yan94@gmail.com> <20210507123528.GA106818@e120877-lin.cambridge.arm.com> From: Dietmar Eggemann Message-ID: Date: Fri, 7 May 2021 15:36:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210507123528.GA106818@e120877-lin.cambridge.arm.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 On 07/05/2021 14:35, Vincent Donnefort wrote: > On Fri, May 07, 2021 at 07:20:31PM +0800, Xuewen Yan wrote: >> From: Xuewen Yan >> >> Last_enqueued_diff's meaning: "diff = util_est.enqueued(p) - task_util(p)". >> When calculating last_enqueued_diff, we add UTIL_AVG_UNCHANGED flag, which >> is the LSB, for task_util, but don't add the flag for util_est.enqueued. >> However the enqueued's flag had been cleared when the task util changed. >> As a result, we add +1 to the diff, this is therefore reducing slightly >> UTIL_EST_MARGIN. > > Unless I miss something it actually depends on the situation, doesn't it? > > if ue.enqueued > task_util(), we remove 1 from the diff => UTIL_EST_MARGIN + 1 > > if ue.enqueued < task_util(), we add 1 to the diff => UTIL_EST_MARGIN -1 I get: ue.enqueued & UTIL_AVG_UNCHANGED = 0 last_enqueued_diff = ue.enqueued_old - ue.enqueued_new last_enqueued_diff = (ue.enqueued | UTIL_AVG_UNCHANGED) - (task_util(p) | UTIL_AVG_UNCHANGED) ^^^^^^^^^^^^^^^^^^^^ added by patch ue.enqueued_old didn't have the flag, otherwise would return earlier task_util(p) could have the LSB set but we just set it to make sure it's set So last_enqueued_diff is 1 larger. But UTIL_EST_MARGIN stays `SCHED_CAPACITY_SCALE / 100` ? Did I miss something here? >> >> Add the flag for util_est.enqueued to have a accurate computation. >> >> Fixes: b89997aa88f0b sched/pelt: Fix task util_est update filtering >> >> Signed-off-by: Xuewen Yan >> --- >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index e5e457fa9dc8..94d77b4fa601 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -3996,7 +3996,7 @@ static inline void util_est_update(struct cfs_rq *cfs_rq, >> if (ue.enqueued & UTIL_AVG_UNCHANGED) >> return; >> >> - last_enqueued_diff = ue.enqueued; >> + last_enqueued_diff = (ue.enqueued | UTIL_AVG_UNCHANGED); >> >> /* >> * Reset EWMA on utilization increases, the moving average is used only >> -- >> 2.29.0 >>