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

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Nov 14, 2007 at 11:27:44AM -0800, Pezza wrote:
> 
> Pasi,
> 
> thanks for your reply.
> 
> I understood from this and other mailing lists that using an HVM machine
> with no PV drivers would result in a poor performance, but it would work
> anyway.
> My problem is that, due to this packet loss, HVM machines are not usable,
> because they get some "strange" errors from time to time (session breaks,
> corrupt files, etc...).
> So you're saying that lack of PV drivers is the cause and thus that HVM
> machines are not stable if we don't use PV drivers?
> 

Basicly, yes.

HVM domU hardware emulation (NIC, disk controller, etc) is done by QEMU in
Xen.

QEMU people can possibly tell you more about expected performance and problems.

And I bet you can find many comparisons with some googling.. performance
with and without PV drivers in HVM domU.

-- Pasi

>                                                                               
>       
> M.
> 
> 
> Pasi Kärkkäinen wrote:
> > 
> > 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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