RE: [Xen-devel] RE: Saving/Restoring IA32_TSC_AUX MSR

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Dan Magenheimer wrote on Fri, 11 Dec 2009 at 08:12:00:

>>> Yes, but code which uses fast vgetcpu is expecting
>>> to get physical cpu and physical node number.  Since
>>> an HVM guest OS only has access to virtual cpu and
>>> virtual node number, the information written to TSC_AUX
>>> by a guest OS is misleading and may silently break any
>>> userland code that assumes it is getting physical
>>> information.
>> 
>> This is depend on how the node info is virtualized.
>> If the virtual node could reflect the physical
>> node info, what rdtscp returns is valuable to applications.
> 
> If it is possible to ensure that the cpu/node info
> is virtualized so that TSC_AUX always correctly provides the
> information needed by apps, I agree this would be
> valuable.  I don't see how this is possible, but maybe
> you have some creative ideas?

It's possible, and the way guest NUMA supposed to be. We are working on that.

Jun
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Intel Open Source Technology Center




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