RE: [Xen-devel] cpufreq support status

["Langsdorf, Mark" <mark.langsdorf@xxxxxxx>]

> Could anyone summarize what the support status of cpu 
> frequency changes is at present. I don't seem to
> recall generic changes to the hpyervisor in
> that respect, but the linux tree has fairly extensive
> changes to the powernow-k8 driver

Keir rewrote and committed patches from me that:
*       allow the dom0 kernel to write to the 
fid/vid k8 pstate control and status MSRs if and 
only if "cpufreq=dom0-kernel" is passed on the 
Xen command line

*       modify time-xen.c to add cpufreq notifier 
support, and to modify the clock frequency
of the hypervisor through a platform hypercall

*       add platform hypercalls to change the 
hypervisor clock frequency and to get the idle 
ticks of all the physical processors
*       make powernow-k8 use the _PSD structure to 
determine what cores in the system share frequencies

still to be done:
*       allow the dom0 kernel to write to the 
architectural pstate control MSR (Opteron 3rd gen
and later processors)

*       modify the cpufreq ondemand governor to use 
the platform hypercall to get the idle load.  I'm
working on this now, but Xen and Linux have different
ideas of what a "tick" is, so it wasn't as simple as
I'd hoped.

*       add the patch to have powernow-k8 only use the 
architectural registers for pstate control for
Opteron 3rd gen and later processors

*       get the _PSD mods accepted into the mainstream
kernel; they were submitted but Dave Jones didn't
commit them for some reason.

> (which would make sense to me only if all other cpufreq
> drivers are fully supported now, too).

I don't understand this; the changes I made in the
Linux tree were not prompted by the Xen code.  What
are you trying to say?

-Mark Langsdorf
Operating System Research Center
AMD



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