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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 AEF16C433ED for ; Wed, 19 May 2021 16:06:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DBDC601FA for ; Wed, 19 May 2021 16:06:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355095AbhESQIC (ORCPT ); Wed, 19 May 2021 12:08:02 -0400 Received: from foss.arm.com ([217.140.110.172]:46862 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354270AbhESQIA (ORCPT ); Wed, 19 May 2021 12:08:00 -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 E2B9F1480; Wed, 19 May 2021 09:06:40 -0700 (PDT) Received: from e120877-lin.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9096D3F73D; Wed, 19 May 2021 09:06:39 -0700 (PDT) Date: Wed, 19 May 2021 17:06:34 +0100 From: Vincent Donnefort To: Dietmar Eggemann Cc: Ingo Molnar , Peter Zijlstra , Xuewen Yan , Juri Lelli , Vincent Guittot , Steven Rostedt , Patrick Bellasi , Quentin Perret , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/fair: Fix util_est UTIL_AVG_UNCHANGED handling Message-ID: <20210519160633.GA230499@e120877-lin.cambridge.arm.com> References: <20210514103748.737809-1-dietmar.eggemann@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210514103748.737809-1-dietmar.eggemann@arm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 14, 2021 at 12:37:48PM +0200, Dietmar Eggemann wrote: > The util_est internal UTIL_AVG_UNCHANGED flag which is used to prevent > unnecessary util_est updates uses the LSB of util_est.enqueued. It is > exposed via _task_util_est() (and task_util_est()). > > Commit 92a801e5d5b7 ("sched/fair: Mask UTIL_AVG_UNCHANGED usages") > mentions that the LSB is lost for util_est resolution but > find_energy_efficient_cpu() checks if task_util_est() returns 0 to > return prev_cpu early. > > _task_util_est() returns the max value of util_est.ewma and > util_est.enqueued or'ed w/ UTIL_AVG_UNCHANGED. > So task_util_est() returning the max of task_util() and > _task_util_est() will never return 0 under the default > SCHED_FEAT(UTIL_EST, true). > > To fix this use the MSB of util_est.enqueued instead and keep the flag > util_est internal, i.e. don't export it via _task_util_est(). > > The maximal possible util_avg value for a task is 1024 so the MSB of > 'unsigned int util_est.enqueued' isn't used to store a util value. > > As a caveat the code behind the util_est_se trace point has to filter > UTIL_AVG_UNCHANGED to see the real util_est.enqueued value which should > be easy to do. > > This also fixes an issue report by Xuewen Yan that util_est_update() > only used UTIL_AVG_UNCHANGED for the subtrahend of the equation: > > last_enqueued_diff = ue.enqueued - (task_util() | UTIL_AVG_UNCHANGED) > > Fixes: b89997aa88f0b sched/pelt: Fix task util_est update filtering > Signed-off-by: Dietmar Eggemann I don't believe this made it through our integration branch testing, so I gave a try manually on my Hikey with LISA's UtilConvergence test. 20 iterations of that test passed without any problem. > --- > kernel/sched/fair.c | 5 +++-- > kernel/sched/pelt.h | 13 +++++++------ > 2 files changed, 10 insertions(+), 8 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 161b92aa1c79..0150d440b0a2 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3856,7 +3856,7 @@ static inline unsigned long _task_util_est(struct task_struct *p) > { > struct util_est ue = READ_ONCE(p->se.avg.util_est); > > - return (max(ue.ewma, ue.enqueued) | UTIL_AVG_UNCHANGED); > + return max(ue.ewma, (ue.enqueued & ~UTIL_AVG_UNCHANGED)); > } Shall we also update proc_sched_show_task() to avoid reading this flag there? -- Vincent