linux-kernel - Re: Problem with commit 31e77c93e432 "sched/fair: Update blocked load when newly idle"

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Date:   Wed, 28 Mar 2018 12:37:32 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Problem with commit 31e77c93e432 "sched/fair: Update blocked load
 when newly idle"

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@...o:~# uname -r
4.16.0-rc4-00198-g31e77c93e432

I'm using openssh-client and openssh-server though.

>>> Bisecting the issue resulted in:
>>>
>>> 31e77c93e432dec79c7d90b888bbfc3652592741 is the first bad commit
>>> commit 31e77c93e432dec79c7d90b888bbfc3652592741
>>> Author: Vincent Guittot <vincent.guittot@...aro.org>
>>> 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.

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