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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 B20ABC433DB for ; Fri, 19 Feb 2021 10:20:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 689A964E5F for ; Fri, 19 Feb 2021 10:20:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230355AbhBSKUF (ORCPT ); Fri, 19 Feb 2021 05:20:05 -0500 Received: from foss.arm.com ([217.140.110.172]:32838 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230281AbhBSKUC (ORCPT ); Fri, 19 Feb 2021 05:20:02 -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 A5F79D6E; Fri, 19 Feb 2021 02:19:16 -0800 (PST) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4C73F3F694; Fri, 19 Feb 2021 02:19:15 -0800 (PST) Subject: Re: [PATCH] sched/pelt: Fix task util_est update filtering To: vincent.donnefort@arm.com, peterz@infradead.org, tglx@linutronix.de, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, patrick.bellasi@matbug.net, valentin.schneider@arm.com References: <20210216163921.572228-1-vincent.donnefort@arm.com> From: Dietmar Eggemann Message-ID: <16e1de11-d221-c572-aec7-4e9a638105a9@arm.com> Date: Fri, 19 Feb 2021 11:19:05 +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: <20210216163921.572228-1-vincent.donnefort@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 16/02/2021 17:39, vincent.donnefort@arm.com wrote: > From: Vincent Donnefort > > Being called for each dequeue, util_est reduces the number of its updates > by filtering out when the EWMA signal is different from the task util_avg > by less than 1%. It is a problem for a sudden util_avg ramp-up. Due to the > decay from a previous high util_avg, EWMA might now be close enough to > the new util_avg. No update would then happen while it would leave > ue.enqueued with an out-of-date value. (1) enqueued[x-1] < ewma[x-1] (2) diff(enqueued[x], ewma[x]) < 1024/100 && enqueued[x] < ewma[x] (*) with ewma[x-1] == ewma[x] (*) enqueued[x] must still be less than ewma[x] w/ default UTIL_EST_FASTUP. Otherwise we would already 'goto done' (write the new util_est) via the previous if condition. > > Taking into consideration the two util_est members, EWMA and enqueued for > the filtering, ensures, for both, an up-to-date value. > > This is for now an issue only for the trace probe that might return the > stale value. Functional-wise, it isn't (yet) a problem, as the value is > always accessed through max(enqueued, ewma). Yeah, I remember that the ue.enqueued plots looked weird in these sections with stale ue.enqueued values. > This problem has been observed using LISA's UtilConvergence:test_means on > the sd845c board. I ran the test a couple of times on my juno board and I never hit this path (util_est_within_margin(last_ewma_diff) && !util_est_within_margin(last_enqueued_diff)) for a test task. I can't see how this issue can be board specific? Does it happen reliably on sd845c or is it just that it happens very, very occasionally? I saw it a couple of times but always with a (non-test) tasks migrating from one CPU to another. > Signed-off-by: Vincent Donnefort Reviewed-by: Dietmar Eggemann [...]