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Re: [Xen-users] XEN - Broadcom issue: survey

On Wed, Nov 14, 2007 at 08:41:43AM -0800, Pezza wrote:
> Hi Pasi,
> Pasi Kärkkäinen wrote:
> > 
> > 4. Make sure networking is OK on HVM domU, make sure you're running 
> >    paravirt drivers on HVM domU (this is important!!). Without PV drivers
> >    performance of HVM domU will be sucky and you WILL get packet drops.
> > 
> Just to be sure I'm not misunderstanding, are you saying that running an HVM
> machine without PV drivers makes it impossible to avoid packets drops? So
> this means there's no way to have a fully functional (=a machine that's
> perfectly usable, regardless of its performance) HVM machine without PV
> drivers?
> I just run some tests following your hints, and my server without xen runs
> fine, with the xen kernel no vms runs fine, the problem comes in a non-PV
> HVM guest only.

HVM guest/domU is _emulating_ a NIC, which is really slow. 

If you're running Linux HVM domU, please install PV drivers to the domU..
this will boost your performance, because then there's no need to emulate a
NIC. If your distribution is not shipping Linux HVM PV drivers, you can get
them from Xen source tree.

HVM domU PV drivers talk directly to Xen and bypass the whole emulation.

At the moment there are no usable PV drivers for Windows HVM domU running on 
opensource Xen. Some people are working on this, but it will take some time
before those drivers are ready/stable.

XenEnterpise, Virtual Iron and Novell SLES have Windows PV drivers available.. 
Redhat is also planning to release their windows drivers at some point.

-- Pasi

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