Re: [Xen-devel] [PATCH 3/8] ACPI: processor: add __acpi_processor_[un]register_driver helpers.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Dec 26, 2011 at 01:31:45AM +0000, Tian, Kevin wrote:
> > From: Konrad Rzeszutek Wilk [mailto:konrad@xxxxxxxxxx]
> > Sent: Friday, December 23, 2011 11:01 AM
> > 
> > > > OK. Lets put the # VCPU != PCPU aside. Say dom0 will boot with all
> > > > CPUs and then later on the admin starts unplugging them.
> > >
> > > This should be communicated to major Xen based distributions, so that it's
> > > an agreed approach since in majority case dom0 is configured as UP or
> > > a few VCPUs.
> > 
> > I am not saying that is it the agreed approach. There has to be
> > flexibility in supporting both. But what I want to understand whether
> > the requirement for VCPU != PCPU can be put aside and put in the drivers
> > later on.
> 
> sure. VCPU!=PCPU requirement is orthogonal to the basic part for gearing
> ACPI information to Xen.
> 
> > 
> > So that the first approach is not changing the generic drivers (much).
> > The reason I am asking about this is two-fold:
> >  1). For new distros (Ubuntu, Fedora), the default is all VCPUs.
> 
> good to know that.
> 
> >      Enterprising users might use dom0_max_vcpus to limit the VCPU count,
> >      but most won't.
> >      Which mean we can concentrate on bringing the _Pxx/_Cxx parsing
> >      up to the hypervisor. Which is really neccessary on any chipset
> >      which has the notion of TurboBoost (otherwise the Xen scheduler
> >      won't pick this up and won't engage this mode in certain
> >      workloads).
> >  2). The ACPI maintainers are busy with ACPI 5.0. I don't know how
> >      much work this is, but it probably means tons of stuff with
> >      embedded platforms and tons of regression testing. So if there
> >      is a patch that does not impact the generic code much (or any)
> >      it will make their life easier. Which also means we can built
> >      on top that for the VCPU != PCPU case.
> > 
> > That is what I am trying to understand.
> 
> no problem. this incremental approach should work.

Excellent. So now the big question  - is this something you would have the
time to do?

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