From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752082AbeC2RlB (ORCPT ); Thu, 29 Mar 2018 13:41:01 -0400 Received: from mail-wr0-f175.google.com ([209.85.128.175]:37025 "EHLO mail-wr0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751164AbeC2Rk7 (ORCPT ); Thu, 29 Mar 2018 13:40:59 -0400 X-Google-Smtp-Source: AIpwx4+uV8yQ7PiJxXVKaiHCtrZbizJ8XwsKYZ5uHrKu1Z2CChm66+4EtV57A7yfuzNCAken7zA/ZQ== Subject: Re: Problem with commit 31e77c93e432 "sched/fair: Update blocked load when newly idle" To: Vincent Guittot , Dietmar Eggemann Cc: "Peter Zijlstra (Intel)" , Ingo Molnar , Linux Kernel Mailing List References: <20180324064627.GA10884@linaro.org> <6b151c56-9ead-7bbe-d1b7-b0e6d69c0d7f@arm.com> From: Heiner Kallweit Message-ID: <796bbd7b-8512-7370-28c9-0f082dc3f287@gmail.com> Date: Thu, 29 Mar 2018 19:40:50 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 29.03.2018 um 09:41 schrieb Vincent Guittot: > On 28 March 2018 at 16:01, Vincent Guittot wrote: >> Hi, >> >> On 28 March 2018 at 12:37, Dietmar Eggemann wrote: >>> Hi, >>> >>> On 03/24/2018 01:47 PM, Heiner Kallweit wrote: >>>> >>>> Am 24.03.2018 um 07:46 schrieb Vincent Guittot: >>>>> >>>>> Hi Heiner, >>>>> >>>>> Le Friday 23 Mar 2018 à 22:28:09 (+0100), Heiner Kallweit a écrit : >>>>>> >>>>>> Recently I started to get the following problems with linux-next: >>>>>> >>>>>> - When working via Putty/SSH on the system the console frequently >>>>>> freezes >>>>>> for few seconds. Sometimes only opening a second console makes the >>>>>> first one react again. >>>>>> >>>>>> - I get "INFO: rcu_sched detected stalls on CPUs/tasks:" warnings as >>>>>> described in [1]. >>>>>> >>> >>> I can't catch this issue on my Juno r0 (arm64 big.Little). >>> >>> root@juno:~# uname -r >>> 4.16.0-rc4-00198-g31e77c93e432 >>> >>> I'm using openssh-client and openssh-server though. >> >> I think that I have finally been able to reproduce it on my hikey >> (octo cortex-A53) after unplugging 6 cores and waiting for almost 2 >> hours >> This seems to happen only on dual core system as I haven't faced that >> before on the hikey which I have used for my tests >> > > I'm finally not so sure that i have the right set up to reproduce the > problem as I haven't been able to reproduce it since. > > Heiner, > > How fast the problem happens on your board ? > Are you doing anything specific on the console that trigger the problem ? > Hi Vincent, the lag when working on the console is constantly there, the "rcu_preempt detected stalls" happens after several hours (so far always within 24h) w/o any triggering event I would be aware of. It occured also when the system was idle at that point in time. Rgds, Heiner > Regards, > Vincent > >>> >>>>>> Bisecting the issue resulted in: >>>>>> >>>>>> 31e77c93e432dec79c7d90b888bbfc3652592741 is the first bad commit >>>>>> commit 31e77c93e432dec79c7d90b888bbfc3652592741 >>>>>> Author: Vincent Guittot >>>>>> Date: Wed Feb 14 16:26:46 2018 +0100 >>>>>> >>>>>> sched/fair: Update blocked load when newly idle >>>>>> >>>>>> When NEWLY_IDLE load balance is not triggered, we might need to >>>>>> update the >>>>>> blocked load anyway. We can kick an ilb so an idle CPU will take >>>>>> care of >>>>>> updating blocked load or we can try to update them locally before >>>>>> entering >>>>>> idle. In the latter case, we reuse part of the nohz_idle_balance. >>>>>> >>>>>> After reversing this commit at least the issue with the freezing console >>>>>> is gone. The second one appeared only sporadically, I still have to see >>>>>> whether it pops up again. >>> >>> >>> [...] >>> >