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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 E3A60C4321D for ; Thu, 16 Aug 2018 15:00:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A172521480 for ; Thu, 16 Aug 2018 15:00:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A172521480 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403992AbeHPR76 (ORCPT ); Thu, 16 Aug 2018 13:59:58 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:37550 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726022AbeHPR75 (ORCPT ); Thu, 16 Aug 2018 13:59:57 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3FB8D7A9; Thu, 16 Aug 2018 08:00:56 -0700 (PDT) Received: from [0.0.0.0] (e107985-lin.emea.arm.com [10.4.12.239]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 710443F5D0; Thu, 16 Aug 2018 08:00:48 -0700 (PDT) Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting To: Quentin Perret Cc: Patrick Bellasi , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan References: <20180806163946.28380-1-patrick.bellasi@arm.com> <20180806163946.28380-4-patrick.bellasi@arm.com> <20180814164905.GG2605@e110439-lin> <7c45c1a8-24cb-6798-5b6f-3b5dfc9b490d@arm.com> <20180815105428.GA7388@e110439-lin> <20180816133249.GA2964@e110439-lin> <20180816133737.xfwfoenbhb5wnndi@queper01-lin> <20180816142115.v7nybc4qfazdiz6n@queper01-lin> From: Dietmar Eggemann Message-ID: <434c550d-65da-1b41-b949-c91b9cfdd127@arm.com> Date: Thu, 16 Aug 2018 17:00:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180816142115.v7nybc4qfazdiz6n@queper01-lin> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/16/2018 04:21 PM, Quentin Perret wrote: > On Thursday 16 Aug 2018 at 15:45:45 (+0200), Dietmar Eggemann wrote: >> On 08/16/2018 03:37 PM, Quentin Perret wrote: >>>>> IMHO, if this is something which should not happen at all, a BUG_ON() is the >>>>> right thing to do here. >>>> >>>> I don't agree on that. I agree it should not happen but since it's a >>>> recoverable error it think we should not panic. >>> >>> FWIW, if this is a recoverable error, I think Linus will agree with >>> Patrick on this one :-) >>> >>> https://lkml.org/lkml/2016/10/4/1 >> >> Yeah, not really agreeing here that this is a recoverable error. > > A non-recoverable scenario could be, for example, if you corrupt your > stack and there is absolutely _nothing_ you can do to keep the system up > and running, because it's just too broken. I don't feel like we're > talking about such an extreme case here ... Yeah, that's the extreme. But what about this lovely BUG_ON(busiest == env.dst_rq) in fair.c's load_balance()? We could recover by just bailing out ;-) I guess we know by now that there are different opinions here. > >> Besides, we >> only consider under-run here, what about over-run? Important thing is to also detect the over-run, i.e. add the first task and the task counter is already > 0. >> >> Currently this warning doesn't hit and if the code will be changed and it >> hits, I still find a BUG_ON more appealing here ... >> >> So this error scenario can happen over and over again and we always recover >> from ? The important thing is that we find the culprit for this behaviour as >> fast as possible ... > > Agreed, we want to debug that ASAP, but WARN should let us do that just > fine, I think. +1.