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

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Date:	Tue, 17 Jan 2012 12:13:14 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Tian, Kevin" <kevin.tian@...el.com>
Cc:	liang tang <liang.tang@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.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>,
	"Yu, Ke" <ke.yu@...el.com>,
	"konrad@...nel.org" <konrad@...nel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"Nakajima, Jun" <jun.nakajima@...el.com>
Subject: Re: [Xen-devel] [PATCH 3/8] ACPI: processor: add
 __acpi_processor_[un]register_driver helpers.

> > I was trying to figure out how difficult it would be to just bring Pxx states to
> > the Xen hypervisor using the existing ACPI interfaces. And while it did not pass
> > all the _Pxx states (seems that all the _PCT, _PSS, _PSD, _PPC flags need to
> > be enabled in the hypercall to make this work), it demonstrates what I had in
> > mind. 

.. snip..
> > 	/* TODO: Under Xen, the C-states information is not present.
> >  	 * Figure out why. */
> 
> it's possible related to this long thread:
> 
> http://lists.xen.org/archives/html/xen-devel/2011-08/msg00511.html
> 
> IOW, Xen doesn't export mwait capability to dom0, which impacts _PDC setting.
> Final solution is to have a para-virtualized PDC call for that.

Aaah. Let me play with that a bit. Thanks for the pointer.

.. snip..
> the prerequisites for this module to work correctly, is that dom0 has the right
> configurations to have all necessary Cx/Px information ready before this 
> module is loaded. That may mean enabling full CONFIG_CPU_IDLE and CONFIG_CPUFREQ,

Right.
> which in current form may add some negative impact, e.g. dom0 will try to control
> Px/Cx to conflict with Xen. So some tweaks may be required in that part.

Yup. Hadn't even looked at the cpufreq tries to do yet.
> 
> given our purpose now, is to come up a cleaner approach which tolerate some
> assumptions (e.g. #VCPU of dom0 == #PCPU), there's another option following this
> trend (perhaps compensate your idea). We can register a Xen-cpuidle and 
> xen-cpufreq driver to current Linux cpuidle and cpufreq framework, which plays 
> mainly two roles:
> 	- a dummy driver to prevent dom0 touching actual Px/Cx
> 	- parse ACPI Cx/Px information to Xen, in a similar way you did above

Yeah, I like where you are heading.
> 
> there may have some other trickiness, but the majority code will be self-contained.

<nods>
> 
> Thanks
> Kevin
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