RE: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes

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

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2007年9月1日 19:07
>
>On 1/9/07 01:23, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>>> Does this affect the available C states, or the current C state of a CPU?
>I
>>> suppose it's the former that matters, since an attempt to deep-sleep
>may
>>> start to fail, which would lead to increased power consumption?
>>
>> Just affect the available C-states and Xen re-evaluates to get new list
>> and thus new decision. Actually that event brings Xen back to C0 out
>> of any C1...Cn. When Xen starts to handle that event, the CPU is
>always
>> in C0 as a running state. :-)
>
>There's only one 'ACPI interrupt line' though, and presumably the re-eval
>happens in dom0 somewhere, sometime later, and possibly on a
>different CPU
>from the one that took the interrupt. What happens if you try and enter a
>C
>state that is no longer available?
>
> -- Keir

Yes, this is even true on native. SCI happens on one CPU with another 
CPU is decided to enter some unavailable C-state at the point. I guess 
hardware should tolerate such invalid request like taking it as a no-op 
or choosing a closest one. Software can anyway issue an invalid request 
to break report from hardware...

Thanks,
Kevin

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