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[Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen

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..
> 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.

> Would the same CONFIG_XEN kernel binary ever not
> run xen_arch_setup(), run on raw hardware, and want

ever not? I am not sure of the question, so let me state:
The Linux kernel if compiled with CONFIG_XEN, and if run on
native hardware, would _never_ run 'xen_arch_setup()'*. It would
run the normal, native type setup.

> to use idle states other than HLT?

*: It could if you really really wanted. You would need to change
the GRUB2 to inject some extra data in the 'sub_hardware' flag to be
the Xen specific.

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