Re: Seeking a KVM benchmark

Paolo Bonzini
2014-11-17T12:22:13Z

On 17/11/2014 13:14, Wanpeng Li wrote:
>>
>>> Sorry, maybe I didn't state my question clearly. As Avi mentioned above
>>> "In VMX we have VPIDs, so we only need to flush if EFER changed between
>>> two invocations of the same VPID", so there is only one VPID if the
>>> guest is UP, my question is if there need a TLB flush when guest's EFER
>>> has been changed?
>> Yes, because the meaning of the page table entries has changed.
>
> So both VMX EFER writes and non-VMX EFER writes cause a TLB flush for UP
> guest, is there still a performance improvement in this case?

Note that the guest's EFER does not change, so no TLB flush happens.
The guest EFER, however, is different from the host's, so if you change
it with a wrmsr in the host you will get a TLB flush on every userspace
exit.

Paolo