Re: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 22/1/08 21:16, "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx> wrote:

>> The Xen hypervisor uses the TSC as a time source.  1st and 2nd
>> generation AMD
>> Operton processors have TSCs that change with frequency under power
>> management.
>> The Xen hypervisor currently cannot cope with the way the TSCs change
>> and the time will regularly go backwards on multicore systems.
> 
> Surely it should be possible to inform Xen of frequency changes (other
> that T-states due to thermal throttling) and hence allow Xen to ensure
> monotonicity? Xen itself does not require that the CPUs run with the
> same rate TSC. It does need to know what frequency they're running at,
> and when they change.

Yes, and that is already done, hooked off the cpu notifier callback chain.
Nobbling the C- and P-state logic shouldn't be necessary.

 -- Keir



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