Re: [4.14] Failing selftest timer/adjtick

Miroslav Lichvar
2021-02-11T11:06:44Z

On Thu, Feb 11, 2021 at 11:33:05AM +0100, Joerg Vehlow wrote:
> > My suggestion for a fix would be to increase the limit in the failing
> > test.
> Thanks, that's what I expected. But I still wonder why the test is failing
> almost 100% of time for me on qemu-arm64 (running on x86). Is this a
> regression in 4.14, that was working at some point or was it never tested on
> arm?

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.

--
Miroslav Lichvar