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

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: liang tang <liang.tang@oracle.com>,
	Konrad Rzeszutek Wilk <konrad@darnok.org>,
	"jeremy@goop.org" <jeremy@goop.org>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"Ian.Campbell@citrix.com" <Ian.Campbell@citrix.com>,
	"mike.mcclurg@citrix.com" <mike.mcclurg@citrix.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stefan.bader@canonical.com" <stefan.bader@canonical.com>,
	"rjw@sisk.pl" <rjw@sisk.pl>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"Yu, Ke" <ke.yu@intel.com>,
	"konrad@kernel.org" <konrad@kernel.org>,
	"lenb@kernel.org" <lenb@kernel.org>,
	"Nakajima, Jun" <jun.nakajima@intel.com>
Subject: Re: [Xen-devel] [PATCH 3/8] ACPI: processor: add __acpi_processor_[un]register_driver helpers.
Date: Tue, 17 Jan 2012 12:13:14 -0500	[thread overview]
Message-ID: <20120117171314.GB5494@phenom.dumpdata.com> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D10FCD37A9@SHSMSX102.ccr.corp.intel.com>

> > 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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