[Bug 210993] Intel frequency scaling causes electrical noise on 10th gen CPUs

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=210993

--- Comment #6 from Karol Herbst (karolherbst@gmail.com) ---
(In reply to Francisco Jerez from comment #5)
> O_o, that's really weird. I guess this could also be some sort of
> electromagnetic interference (E.g. with your soundcard?  Does the problem
> occur with the loudspeakers turned off?), or an issue with your PSU.
> 

It is very quiet. Definitely you can hear it only with slowly spinning fans and
no background noise. Searching through the web it sounds like a common issue
and disabling sleep states is supposed to be the proper "fix" for this.

But at least muting the speakers don't help.

> The apparent frequency dropping below scaling_min_freq might be an artifact
> of how the busy frequency of a CPU thread is calculated: It should
> approximate the ratio of executed clock cycles to the time it spent in C0
> state, which can deviate from its actual working frequency if the processor
> enters and exits some C1+ state repeatedly since the transition may have
> some significant latency.  According to your turbostat log the CPU cores
> that report a busy frequency below scaling_min_freq seem to be handling
> quite a few interrupts which is consistent with that explanation.  It
> doesn't necessarily indicate a power management bug.
> 
> Does disabling some specific idle state (e.g via
> /sys/devices/system/cpu/cpu*/cpuidle/state*/disable) have any effect on the
> noise?

disabling all except state0 stops the noise.

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