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,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,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 39322C11F64 for ; Thu, 1 Jul 2021 10:34:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 183EA6145F for ; Thu, 1 Jul 2021 10:34:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236061AbhGAKhW (ORCPT ); Thu, 1 Jul 2021 06:37:22 -0400 Received: from outbound-smtp20.blacknight.com ([46.22.139.247]:40135 "EHLO outbound-smtp20.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235300AbhGAKhV (ORCPT ); Thu, 1 Jul 2021 06:37:21 -0400 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp20.blacknight.com (Postfix) with ESMTPS id 2FA531C3FF5 for ; Thu, 1 Jul 2021 11:34:50 +0100 (IST) Received: (qmail 25466 invoked from network); 1 Jul 2021 10:34:50 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.255]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 1 Jul 2021 10:34:49 -0000 Date: Thu, 1 Jul 2021 11:34:48 +0100 From: Mel Gorman To: Sachin Sant Cc: Odin Ugedal , Vincent Guittot , Peter Zijlstra , Naresh Kamboju , Ingo Molnar , open list Subject: Re: [PATCH] sched/fair: Ensure _sum and _avg values stay consistent Message-ID: <20210701103448.GL3840@techsingularity.net> References: <20210624111815.57937-1-odin@uged.al> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 01, 2021 at 03:17:16PM +0530, Sachin Sant wrote: > > > > On 24-Jun-2021, at 4:48 PM, Odin Ugedal wrote: > > > > The _sum and _avg values are in general sync together with the PELT > > divider. They are however not always completely in perfect sync, > > resulting in situations where _sum gets to zero while _avg stays > > positive. Such situations are undesirable. > > > > This comes from the fact that PELT will increase period_contrib, also > > increasing the PELT divider, without updating _sum and _avg values to > > stay in perfect sync where (_sum == _avg * divider). However, such PELT > > change will never lower _sum, making it impossible to end up in a > > situation where _sum is zero and _avg is not. > > > > Therefore, we need to ensure that when subtracting load outside PELT, > > that when _sum is zero, _avg is also set to zero. This occurs when > > (_sum < _avg * divider), and the subtracted (_avg * divider) is bigger > > or equal to the current _sum, while the subtracted _avg is smaller than > > the current _avg. > > > > Reported-by: Sachin Sant > > Reported-by: Naresh Kamboju > > Signed-off-by: Odin Ugedal > > Hello Odin, Vincent, > > The issue of kernel warning(during boot) seen on Power sever, reported few days back is not completely fixed. > I am able to recreate this issue with latest 5.13 kernel(which has this fix) > > # git log --oneline kernel/sched/fair.c > a6eaf3850cb1 Merge tag 'sched-urgent-2021-06-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip > 54a728dc5e4f Merge tag 'sched-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip > 1c35b07e6d39 sched/fair: Ensure _sum and _avg values stay consistent <<== > What was HEAD when you checked this? 1c35b07e6d39 was merged in the 5.14-rc1 merge window so would not be in 5.13. # git log v5.13..origin/master --pretty=one | grep 1c35b07e 1c35b07e6d3986474e5635be566e7bc79d97c64d sched/fair: Ensure _sum and _avg values stay consistent It's not tagged for stable and lacks a Fixes: tag so I don't think it'll be automatically picked up for 5.13-stable unless Odin sends it to stable@vger.kernel.org. -- Mel Gorman SUSE Labs