RE: RE: RE: RE: RE: RE: [Xen-devel] No C-States any longer...(it's not over!)

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Carsten Schiers [mailto:carsten@xxxxxxxxxx]
> Sent: Monday, June 27, 2011 7:13 PM
> 
> I thought by buying a new mainboard, I could solve the issue. It is not the 
> case.
> 
> >> >In your case there's no _CST found, and then no PBLK found.
> >...
> >w/o PBLK, FADT info is incomplete to construct a full Cstate information.
> 
> The new mainboard now implements a PBLK for the first CPU in FADT, but
> latencies for C2/C3
> are > 100/1000, which is the semantic to disable it (I read).
> 
> But no change in xenpm output, there are still no C-States.
> 
> I think acpi_processor_get_power_info_default is called too late. In old,
> working 2.6.18 code,
> a similar function acpi_processor_get_power_info_default_c1 is called as very
> first function in
> acpi_processor_get_power_info, to setup C1 which is mandatory for all CPUs.

this is the generic Linux ACPI logic, so you may report to Linux upstream for 
their
opinion.

> 
> Some other thoughts where I see the code needs changes:
> 
>   - even if spec says that either PBLK or _CST should implement, C1 should be
> set up (solves issue with mainboard 1)
>   - when C2/C3 are above limits (100/1000), C1 still should be set up (solves
> issue with mainboard 2)

yes, I agree that C1 should be always present regardless of platform difference,
as long as cpuidle is enabled in Xen. I'll try to work out a patch and CC you 
when
it's ready.

Thanks
Kevin

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