Re: Power management

[BERTRAND Joël <joel.bertrand%systella.fr@localhost>]

Jonathan A. Kollasch a écrit :
> 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).

	Thanks a lot for your answer. Now I only have to find a fix to my
dom0's panic ;-)

	Regards,

	JKB