Re: KVM Processor cache size

Avi Kivity
2010-08-03T05:38:49Z

On 08/03/2010 02:38 AM, Anthony Liguori wrote:
> Is there already a way to communicate from the target to the source?
> This would allow to check for migrate-ability before we transfer any
> data. Or should we handle this in a management application?

Since this is determined at startup time, it should be done by
management. There's no point in starting a live migration that we know
will fail.

>
> Send the cpuid fields as part of migration state. Verify they match
> the local cpuid fields on the destination side. The destination can
> then reject the migration if it can't match those CPUID fields.

I agree with that, as a safety check.

Note it can be determined even earlier, if qemu warns/fails on masked
features:

qemu -cpu qemu64,+this,-that,strict

> That's actually the only way to safely do it today because there's no
> way for a management application to query qemu and kvm for the fields
> that they'll mask out.

That needs to part of the qemu capabiltities megapatch. Supporting
POPCNT isn't very different from supporting cache=unsafe from the
management point of view.

--
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signature is too narrow to contain.