RE: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron2nd gen and earlier processors

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

>From:Keir Fraser
>Sent: 2008年1月23日 5:52
>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

I remembered Mark is the one to add that notification interface,
and so also interested why this patch is required... unless those
early stepping as some processor-initiated freq change... 

Thanks,
Kevin

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