Sterling Windmill wrote:
I've read that it's possible to live migrate KVM guests between Intel
> and AMD CPUs, is it also possible to migrate from a CPU without
> NPT/EPT to the Phenom II that supports NPT?
Yes.
> Will I lose out on
> any of the benefits NPT allows without shutting down and restarting
> the guest?
NPT/EPT is a hypervisor feature, so the guest is unaffected (left alone
the performance benefit). The guest does it's own paging (the same as on
native), so the actual hypervisor page handling is not visible to the
guest. You will immediately benefit from NPT if you migrate from a
non-EPT/NPT capable host.
Cross-vendor migration experience differs from guest to guest, the most
important point to look at are the CPUID bits. Start with a conservative
setting (like -cpu kvm64 if you have a recent qemu-kvm) and if in need
turn on features that you need (which must be on both hosts).
Also use recent KVM kernel modules, some CVM related bugs have been
fixed lately.
We have tried migrating several guests without issues between non-NPT
and NPT hosts.
If you experience problem, feel free to mail me with a description.
Also, any thoughts on how much more performant a 3.0GHz Phenom II will be for running KVM guests than the 2.4GHz Intel Q6600?
NPT is faster than shadow paging on almost all workloads (since it
avoids most of the #VMEXITs), but since the virtualization
implementation differs in many details between Intel and AMD,
performance estimation just based on this single feature is not very
legitimate.
Regards,
Andre.
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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