Re: [Xen-users] xen 3.1 and 32bit guests in 64bit dom0

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> PV is faster than HVM, but HVM allows unmodified guest OSs, so it's not
> a clear cut case for which is better.

PV has good performance.  Performance of 32-bit PV guests (on either a 32-bit 
or a 64-bit hypervisor) is probably higher than that of a 64-bit PV guest.  I 
don't know how well 64-bit PV guests compare to 64-bit HVM guests (which 
could potentially still have PV drivers installed) because implementing full 
PV on 64-bit was hard to do as efficiently as on 32-bit.  It may be that HVM 
is more competitive for performance in the case of 64-bit guests.

> PV has better performance, but if 
> you have to use a non-Xenified kernel, then I guess your hands are tied
> (although apparently there is now some domU support in the standard
> kernel according to kerneltrap.org).

The 2.6.23 development tree (which has just passed -rc1) includes support for 
Xen.  If you select a Xen capable host architecture (Pentium Pro and above) 
then there'll be an option to support Xen under the paravirtualisation 
support section.

The resulting kernel build will be capable of booting native or on Xen.  
However you'll need to use the vmlinux / vmlinuz on Xen, whereas native 
booting will still need the bzImage.  There's work underway to allow Xen to 
boot bzImages directly, so you'll only need to keep one image around.

Cheers,
Mark

> As you've got hardware support, the only thing you need is to set the
> config file and disk image up properly.  HVM domains boot just like
> regular systems (they have a BIOS as well), and so require a boot loader
> in the disk image (I use an image for the entire disk, I don't know if
> you can split it up into different files for different partitions with
> HVM), along with the kernel etc, and in the config file for the domain
> you need to remove the initrd line, point the kernel line to the
> hvmloader, change the builder to hvm and add the device modeller etc.
> You can find an example in /etc/xen/xmexample.hvm in the standard Xen
> install, or you could use RedHat's virt-manager/virt-install to
> configure and install the domain.
>
> Hope this helps,
>
> Martin
>
> Lorin wrote:
> > On 7/26/07, Martin Goldstone <m.j.goldstone@xxxxxxxxxxxxxxx> wrote:
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA1
> >>
> >> 1st question:  Is the domU kernel actually a Xen kernel?  By the look of
> >> that error, I'd guess that it isn't, especially as normally Xen kernels
> >> have -xen in them somewhere, and yours ends in -smp.  You need to have a
> >>  Xen kernel to do PV, or you have to use HVM.
> >
> > It's not a Xen kernel but a plain old stock kernel on which I'm
> > supposed to run the VM (application requirements ).
> > I have VT support in the cores so HVM should be enabled from what I've
> > read so far . Does it require anything else ?
> >
> > Speaking of PV and HVM  the latter is better because it makes use of
> > hardware support right ?
> >
> >> 3rd question:  If Danilo Godec's suggestion about the NIC driver doesn't
> >> work, could you give us some more details about your networking setup
> >> (ie NIC make/model, Bonding, VLANs etc)?
> >
> > Yeah, it was the bnx2 problem.
> >
> > Thanks a lot!



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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