Re: paravirtualization & cr3-cache feature

["Joerg Roedel" <joerg.roedel-5C7GfCeVMHo@public.gmane.org>]

On Sat, Feb 10, 2007 at 02:22:25PM -0800, Dor Laor wrote:
> 
> >hi,
> >    Can someone briefly explain what the cr3-cache feature on intel VT
> >processors is and how it is used to improve performance in
> >paravirtualization.
> 
> In short, this is a unique Intel VT feature that supposed to save vmexit
> on cr3 switch. The vmexit operation is quite expensive at the moment
> (something like 2-5 ms!). PV kernels can use this feature by sharing
  ^^^^^^^^^^^^^^^^^^^^^^^^

Where do you measured this unbelievable large number? On AMD-V I
measured around 2400 processor cycles for a VMEXIT/VMENTRY roundtrip. I
would really really wonder if Intel-VT is that slow...

Joerg

-- 
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG



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