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Subject: Re: WARNING: CPU: 112 PID: 2041 at kernel/sched/sched.h:1453
To:     Bruno Goncalves <bgoncalv@redhat.com>
Cc:     CKI Project <cki-project@redhat.com>, linux-kernel@vger.kernel.org,
        nathan@kernel.org, Memory Management <mm-qe@redhat.com>,
        linux-arm-kernel@lists.infradead.org
References: <CA+QYu4oOgrb8n=Qyuky-M0dYPEo_HNMdbNuj2SF4a=aQTE_xvw@mail.gmail.com>
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From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <f5b4beb9-4e75-0f4e-da8b-b7ccc12fee68@arm.com>
Date:   Thu, 29 Jul 2021 16:38:10 +0200
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On 29/07/2021 14:36, Bruno Goncalves wrote:
> On Wed, Jul 28, 2021 at 5:55 PM Dietmar Eggemann
> <dietmar.eggemann@arm.com> wrote:
>>
>> On 28/07/2021 15:11, Bruno Goncalves wrote:

[...]

>> Can't reproduce it on my Juno (arm64) (slow-switching (scpi-cpufreq
>> driver)).
> 
> We seem to be able to reproduce this only on Ampere Altra machines,
> specifically on mtjade and mtsnow cpus.
> 
> # cpupower frequency-info
> analyzing CPU 0:
>   driver: cppc_cpufreq
>   CPUs which run at the same hardware frequency: 0
>   CPUs which need to have their frequency coordinated by software: 0
>   maximum transition latency:  Cannot determine or is not supported.
>   hardware limits: 1000 MHz - 2.80 GHz
>   available cpufreq governors: conservative ondemand userspace
> powersave performance schedutil
>   current policy: frequency should be within 2.00 GHz and 2.80 GHz.
>                   The governor "schedutil" may decide which speed to use
>                   within this range.
>   current CPU frequency: 1.55 GHz (asserted by call to hardware)
> 
> # ps -eTo comm,pid,pri,class | grep sugov
> sugov:0            1082 140 DLN
> sugov:1            1085 140 DLN
> ...
> sugov:78           1319 140 DLN
> sugov:79           1320 140 DLN

Thanks! In the meantime I got access to an Ampere Altra so I can try
5.14.0-rc1 later today.