linux-kernel - RE: [Xen-devel] [PATCH 3/8] ACPI: processor: add __acpi_processor_[un]register

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Date:	Mon, 26 Dec 2011 01:31:45 +0000
From:	"Tian, Kevin" <kevin.tian@...el.com>
To:	Konrad Rzeszutek Wilk <konrad@...nok.org>
CC:	"jeremy@...p.org" <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"mike.mcclurg@...rix.com" <mike.mcclurg@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stefan.bader@...onical.com" <stefan.bader@...onical.com>,
	"rjw@...k.pl" <rjw@...k.pl>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"liang.tang@...cle.com" <liang.tang@...cle.com>,
	"Yu, Ke" <ke.yu@...el.com>,
	"konrad@...nel.org" <konrad@...nel.org>,
	"lenb@...nel.org" <lenb@...nel.org>
Subject: RE: [Xen-devel] [PATCH 3/8] ACPI: processor: add
 __acpi_processor_[un]register_driver helpers.

> From: Konrad Rzeszutek Wilk [mailto:konrad@...nok.org]
> 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.

Thanks
Kevin
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