linux-kernel - Re: [Xen-devel] [RFC] acpi processor and cpufreq harester - aka pipe all of that up to the hypervisor (v3)

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Date:	Tue, 14 Feb 2012 20:30:06 +0200
From:	Pasi Kärkkäinen <pasik@....fi>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	ke.yu@...el.com, kevin.tian@...el.com, JBeulich@...ell.com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	xen-devel@...ts.xensource.com
Subject: Re: [Xen-devel] [RFC] acpi processor and cpufreq harester - aka
	pipe all of that up to the hypervisor (v3)

On Tue, Feb 14, 2012 at 12:06:46AM -0500, Konrad Rzeszutek Wilk wrote:
> 
> This "harvester" (I am horrible with names, if you have any suggestions please
> tell me them) collects the information that the cpufreq drivers and the
> ACPI processor code save in the 'struct acpi_processor' and then sends it to
> the hypervisor.
> 

Btw there's a typo in the subject line.. "harester".

I'm not very good with names either: collector? passthru? 


> The driver can be either an module or compiled in. In either mode the driver
> launches a thread that checks whether an cpufreq driver is registered. If so
> it reads all the 'struct acpi_processor' data for all online CPUs and sends
> it to hypervisor. The driver also register a CPU hotplug component - so if a new
> CPU shows up - it would send the data to the hypervisor for it as well.
> 
> I've tested this with success on a variety of Intel and AMD hardware (need
> a patch to the hypervisor to allow the rdmsr to be passed through). The one
> caveat is that dom0_max_vcpus inhibits the driver from reading the vCPUs
> that are not present in dom0. One solution is to boot without dom0_max_vcpus
> and utilize the 'xl vcpu-set' command to offline the vCPUs. Other one that
> Nakajima Jun suggested was to hotplug vCPUS in - so bootup dom0 and hotplug
> the vCPUs in - but I am running in difficulties on how to do this in the hypervisor.
> 

When using this driver do you need to pass any options to Xen hypervisor? 
(cpufreq=something) ? 

It might be good to mention something about that in the patch comments.

-- Pasi

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