Re: cpuidle flag

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Tue, Dec 10, 2024 at 07:45:50PM +0000, Mike wrote:
> Elliott Mitchell wrote:
> > try adding "cpuidle" to Xen's command-line.
> 
> This does nothing.  Per the wiki, it's enabled by default since Xen 3.4.
> I confirmed that with `xenpm get-cpuidle-states`.

Are you sure?

With 4.11 I had to deliberately enable "cpuidle" AND load the
"xen_acpi_processor.ko" module.  Otherwise Xen only had C1 (hlt
instruction) and not C2 or greater.

Other trick is "xen_acpi_processor.ko" only enables C-states for which
Domain 0 had corresponding vCPUs.  Presently I'm having to give Domain 0
the maximum vCPUs, then use `xl vcpu-set` to offline most of them.

I haven't yet chased this down.  Debug information from
"xen_acpi_processor.ko" suggests there are 2 loops for uploading ACPI
states.  The first one uploads both P and C states, but only runs on
processors for which Domain 0 has a corresponding vCPU.  The second runs
for processors which have no Domain 0 vCPU, but only uploads P-states.


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