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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8CE4C433F5 for ; Fri, 15 Apr 2022 03:56:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347317AbiDOD7G (ORCPT ); Thu, 14 Apr 2022 23:59:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237942AbiDOD7B (ORCPT ); Thu, 14 Apr 2022 23:59:01 -0400 Received: from mailgw02.mediatek.com (unknown [210.61.82.184]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE0D3A56CC for ; Thu, 14 Apr 2022 20:56:33 -0700 (PDT) X-UUID: 02f24ce5f2d342ed88708e41b49d6325-20220415 X-UUID: 02f24ce5f2d342ed88708e41b49d6325-20220415 Received: from mtkexhb01.mediatek.inc [(172.21.101.102)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-SHA384 256/256) with ESMTP id 84804821; Fri, 15 Apr 2022 11:56:29 +0800 Received: from mtkcas11.mediatek.inc (172.21.101.40) by mtkmbs10n1.mediatek.inc (172.21.101.34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.792.15; Fri, 15 Apr 2022 11:56:28 +0800 Received: from mtksdccf07 (172.21.84.99) by mtkcas11.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 15 Apr 2022 11:56:27 +0800 Message-ID: <231503cb93caabb5fc0e1027423e971560493075.camel@mediatek.com> Subject: Re: [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method From: Kuyo Chang To: Peter Zijlstra CC: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , "Ben Segall" , Mel Gorman , "Daniel Bristot de Oliveira" , Matthias Brugger , , Ingo Molnar , , , Date: Fri, 15 Apr 2022 11:56:27 +0800 In-Reply-To: References: <20220414090229.342-1-kuyo.chang@mediatek.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-MTK: N Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2022-04-14 at 16:44 +0200, Peter Zijlstra wrote: > I've taken the liberty of carrying over the tags from v2 and reworked > the Changelog a little. Thank you for all your assistance. > --- > Subject: sched/pelt: Fix attach_entity_load_avg() corner case > From: kuyo chang > Date: Thu, 14 Apr 2022 17:02:20 +0800 > > From: kuyo chang > > The warning in cfs_rq_is_decayed() triggered: > > SCHED_WARN_ON(cfs_rq->avg.load_avg || > cfs_rq->avg.util_avg || > cfs_rq->avg.runnable_avg) > > There exists a corner case in attach_entity_load_avg() which will > cause load_sum to be zero while load_avg will not be. > > Consider se_weight is 88761 as per the sched_prio_to_weight[] table. > Further assume the get_pelt_divider() is 47742, this gives: > se->avg.load_avg is 1. > > However, calculating load_sum results in 0: > > se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum, > se_weight(se)); > se->avg.load_sum = 1*47742/88761 = 0. > > Then enqueue_load_avg() adds this to the cfs_rq totals: > > cfs_rq->avg.load_avg += se->avg.load_avg; > cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum; > > Resulting in load_avg being 1 with load_sum is 0, which will trigger > the WARN. > > Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq > and its se") > Signed-off-by: kuyo chang > [peterz: massage changelog] > Signed-off-by: Peter Zijlstra (Intel) > Reviewed-by: Vincent Guittot > Tested-by: Dietmar Eggemann > Link: > https://urldefense.com/v3/__https://lkml.kernel.org/r/20220414090229.342-1-kuyo.chang@mediatek.com__;!!CTRNKA9wMg0ARbw!35Im02xxIuUZdLYpPng37Yk7oVNJVJ1tfbu4XRzlq-6VhH3K29Por0gJCFlslT_CMgA$ > > --- > kernel/sched/fair.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3829,11 +3829,11 @@ static void attach_entity_load_avg(struc > > se->avg.runnable_sum = se->avg.runnable_avg * divider; > > - se->avg.load_sum = divider; > - if (se_weight(se)) { > - se->avg.load_sum = > - div_u64(se->avg.load_avg * se->avg.load_sum, > se_weight(se)); > - } > + se->avg.load_sum = se->avg.load_avg * divider; > + if (se_weight(se) < se->avg.load_sum) > + se->avg.load_sum = div_u64(se->avg.load_sum, > se_weight(se)); > + else > + se->avg.load_sum = 1; > > enqueue_load_avg(cfs_rq, se); > cfs_rq->avg.util_avg += se->avg.util_avg;