RE: [Xen-devel] [PATCH 3/8] ACPI: processor: add__acpi_processor_[un]register_driver helpers.

From: Tian, Kevin
Date: Sun Dec 25 2011 - 20:31:59 EST

> 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.

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