Re: Power management

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Mon, Oct 26, 2020 at 10:07:29AM +0100, BERTRAND Joël wrote:
> 	Hello,
> 
> 	I'm trying to use power management or clock modulation with NetBSD/XEN
> dom0. estd aborts with :
> 
> estd: Cannot get supported frequencies (maybe you forced the wrong
> CPU-scaling technology?)
> 
> 	Of course, dom0 kernel contains estd support. I have tried some other
> options like cpufreq=xen directly in hypervisor and without success.
> 
> 	Is it possible to use estd in dom0 ? I have found a very old thread
> (2009) but solution cannot be applied to a recent NetBSD dom0.
> 
> 	Best regards,
> 
> 	JKB

Xen needs the dom0 to feed it information from ACPI for this to work.
This is not currently implemented in NetBSD dom0.

For more modern CPUs though, particularly those with turbo mode, this isn't
entirely necessary, as the CPU itself will automatically reduce its frequency
when idle.  I can speak from experience (observing with a power meter on the
computer) that this is true for Sandy Bridge and newer Intel.  I know though
that AMD Fam10h (w/o turbo) and older aren't that advanced, and will just run
at the speed they're told.  Not sure when AMD's CPUs started doing automatic
frequency reduction at idle, but I expect it may have coincided with the
introduction of turbo (I have no AMD newer than "Deneb" to check).