Re: [Xen-users] HVM and Intel VT processors

[Javier Guerra <javier@xxxxxxxxxxx>]

On Wed, Jan 28, 2009 at 9:20 AM, Ma-ris Ruskulis <maris@xxxxxxxx> wrote:
> Hello!
> I'm wondering about installing windows server on xen-hvm, I have VT
> enabled cpu's. Do I need install GPLPW drivers to get better
> performance? Or the cpu's will do that work? As stands here:
> http://www.virtuatopia.com/index.php/An_Overview_of_Virtualization_Techniques#Hardware_Virtualization
> then VT enabled cpu's will enshure. that unmodified guest virtual
> machines will run without the overheads. Is this true?

it's a common misconception that VT features give some kind of
performance benefits; but it's totally wrong.

VT features just make it possible to virtualize almost the whole CPU
without resorting to software emulation.  that's what HVM guests are.

but the rest of the hardware (especially storage, network, and display
devices) is still emulated in software.  VT doesn't do a thing there.

PV drivers bring the performance benefits of paravirtualization to the
parts of a closed OS (windows) that can be replaced: device drivers.


in short:  fully PV guests can only run modifiable (open source,
mostly) OSs.  for non-modifiable (windows) OSs you need VT, but
periferals are emulated, thus slow.  PV drivers fix that.

-- 
Javier

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users