Re: NetBSD Dom0 and (kind of) power management

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On 18.03.11 05:49, Jukka Ruohonen wrote:
> On Fri, Mar 11, 2011 at 01:04:05AM +0100, Jean-Yves Migeon wrote:
>> It needs ACPI work within NetBSD, oriented towards Xen. Most of the
>> machinery currently used for x86 can be reused I think, the missing part
>> being the code that will feed hypervisor with the information obtained
>> via ACPI.
> 
> Can you outline the general problems involving ACPI and Xen? These issues
> needs to be fixed sooner or later, given that the former is mandatory for
> things like NUMA, etc.
> 
> In another thread:
> 
>> Power management under Xen requires ACPI support, as the hypervisor 
>> does not implement extensive power management routines. Today's machines 
>> requires ACPI parsing to query/obtain information regarding almost 
>> everything, including PM, and this task is devoted to dom0. The support 
>> is missing for NetBSD.
> 
> Looking at the Xen 4.0 sources, it contains Linux's in-kernel frequency
> governor, among other things. So I guess it actually implements most of the
> power management features available on Linux? But that seems to be closely
> tied to the machine-dependent Linux drivers and APIs [1]. So I guess it is
> likely that it will never work in NetBSD. Nor would it be desirable (or even
> possible) to mimic Linux for the sake of Xen, IMO.

The key point is that the Dom0 has virtual cpus. And you don't know
which vcpu is scheduled on which physical cpu.

Dom0 has to invoke hypercalls for all kind of things that must happen
on the physical cpus.
C- and P-States belong to those "things".

Christoph

> - Jukka.
> 
> [1] http://wiki.xensource.com/xenwiki/xenpm
>