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Subject: Re: [4.14] Failing selftest timer/adjtick
To:     Miroslav Lichvar <mlichvar@redhat.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>, stable@vger.kernel.org,
        Ingo Molnar <mingo@kernel.org>,
        John Stultz <john.stultz@linaro.org>
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From:   Joerg Vehlow <lkml@jv-coder.de>
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Date:   Thu, 18 Feb 2021 08:05:39 +0100
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Hi Miroslav,

On 2/11/2021 11:59 AM, Miroslav Lichvar wrote:
> I don't think it is specific to arm or that it is a regression. I
> think the virtual machine just happens to be too idle for the test.
> There may be unrelated changes, maybe in the kernel, qemu, or
> applications, that caused the rate of the clock updates to decrease so
> much that the instability now triggers the failure in the test.  The
> issue with the clock was there since NO_HZ was introduced, but it
> becomes more severe as the activity of the kernel decreases.
Thank you for that explanation. I did create some background load (copy 
from urandom to null) and ran the test. This made the test pass every time.

Jörg