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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Message-ID: <20120215163340.GD4093@phenom.dumpdata.com>
Date:	Wed, 15 Feb 2012 11:33:41 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Pasi Kärkkäinen <pasik@....fi>
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 08:30:06PM +0200, Pasi Kärkkäinen wrote:
> 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".

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

"passthru" sounds better.
> 
> 
> > 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) ? 

No need. You only need that if you want to change the default cpufreq driver from
the ondemand to performance (so cpufreq=performance) or want more verbose information:
cpufreq=verbose,performance

By default the Xen hypervisor will take the cpufreq data in account unless you
override that with 'dom0-is-deciding-power-management-and-I-cant-remember-exactly'
parameter.

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

I will include cpufreq=verbose and mention that the effect before and after. And also
with xenpm.

Thanks!
> 
> -- Pasi
> 
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