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    SubjectRe: [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".

    > 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:

    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'

    > 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.

    > -- Pasi
    > --
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