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

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Date:   Fri, 30 Mar 2018 08:50:22 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        "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"

On 29 March 2018 at 19:40, Heiner Kallweit <hkallweit1@...il.com> wrote:
> Am 29.03.2018 um 09:41 schrieb Vincent Guittot:

>>
>> 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.

Ok, so I don't have the problem on my hikey as the console never lag
on my setup.

Can you send me the config of  your kernel ? I'd like to check if you
have enable something that could trigger such problem

Thanks,
Vincent

>
> Rgds, Heiner
>
>> Regards,
>> Vincent
>>
>>>>
>>>>>>> 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.
>>>>
>>>>
>>>> [...]
>>>>
>>
>