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    SubjectRe: [Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen
    On 03/24/2011 12:05 PM, Konrad Rzeszutek Wilk wrote:
    > On Thu, Mar 24, 2011 at 03:18:14AM -0400, Len Brown wrote:
    >> Is a CONFIG_XEN kernel supposed to use just HLT in idle?
    > For right now..

    For always, I should think.

    >> xen_arch_setup() does this:
    >>
    >> pm_idle = default_idle;
    >> boot_option_idle_override = IDLE_HALT;
    >>
    >> which has that effect. I guess this makes sense b/c the
    >> CONFIG_XEN kernel is Dom0 and the real C-sates are done
    >> by the hypervisor?
    > Correct. There are some patches that make the C-states
    > be visible in the Linux kernel, but that hasn't been ported
    > over yet.

    All we need is for the idle CPU to block in the hypervisor; a plain
    "hlt" is always going to be sufficient (which is overridden as a pvop
    into a sched_idle hypercall).

    Xen will choose an appropriate power state for the physical cpus
    depending on the overall busyness of the system (which any individual
    virtual machine can't determine).

    J


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