Hi!
> Update:
>
> Kernel 2.6.18-r4
>
> I've done some more testing, and I've narrowed the problem down to the
> "processor" cpu driver.
> I disabled all power management features in the kernel, and compiled
> ACPI as modules so that they would not be loaded until I wanted them to be.
>
> APM is off.
> CPU Frequency Scaling is off.
> ACPI is compiled entirely as modules to be loaded by the user.
>
> While running on the battery:
> As soon as I "modprobe processor" the humming begins, and as soon as I
> "rmmod processor" the humming stops.
>
> While running on AC, if I "modprobe processor" there is no buzzing. I
> can remove the AC adapter and the computer remains silent.
Try the following:
cat /proc/acpi/processor/*/power in the following situations:
1) After loading the processor module being on the battery,
2) After loading the processor module being on AC,
3) After disconnecting the AC,
and compare the results. I think that for 1), you will see more C-states than
for 2) and that possibly the missing C-states are not added for 3).
>
> It seems to be something related to the way that the processor driver is
> handling power to the CPU. Ideas?
It looks that when your machine doesn't hum, it doesn't save so much power.
Try to change the timer frequency, I suspect that frequency of the hum tracks
it. Try to set it at 1000 Hz if it's not already there; possibly at this
frequency, capacitors will do better work and filter the peaks on the power
bus better. You can also use 100 Hz - maybe the hum will go lower and will be
less hearable.
With regards, Pavel Troller
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