Re: [Xen-devel] Questions about hvm domU default devices with upstream qemu

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 4 Sep 2013, Fabio Fantoni wrote:
> Il 04/09/2013 15:17, Stefano Stabellini ha scritto:
> > On Wed, 4 Sep 2013, Fabio Fantoni wrote:
> > > Il 04/07/2013 15:51, Fabio Fantoni ha scritto:
> > > > Last year I posted a question about default devices of upstream qemu
> > > > that
> > > > differ from qemu traditional, like empty floppy and cdrom in particular.
> > > > About empty floppy now is disabled as workaround.
> > > > About empty cdrom Stabellini tells that is useful, so I tried to use it
> > > > but
> > > > cd-insert was failing,and I must define other empty cdrom on xl
> > > > configuration file, for example with: ',raw,hdb,ro,cdrom'.
> > > > It seem that there isn't default devices usable without define them in
> > > > xen,
> > > > and I think that probably need to revise the definition of the devices
> > > > to
> > > > avoid empty and unusable ones and to do everything as best as possible
> > > > (also
> > > > with possibly reviewing qemu side).
> > > > Another good thing is also consider pv domU case and possible future
> > > > support
> > > > of spice and/or other useful features.
> > > > Thanks for any reply.
> > > I seen no replies about this, I think is important improve upstream qemu
> > > support and remove the traditional ASA upstream will be equivalent or
> > > superior
> > > in all features.
> > > 
> > > I also think is good idea add q35 support on xen.
> > > Seem that hvm domUs have performance limits, in particular on windows
> > > domUs
> > > (also with pv drivers) caused probably by old hardware emulation by qemu
> > > and/or xen support limited on some instruction sets.
> > > I don't know how to add essential q35 support on hvmloader to do some
> > > tests
> > > and have effective data about improvements.
> > > Anyone on this?
> > I agree that this is important and thanks for raising the issue.
> > It would be nice if somebody stepped up to do the q35 work.
> 
> Thanks for reply, can you reply also on questions about default devices with
> upstream qemu please?

I think it might be a good idea to keep the same set of default devices
between qemu-traditional and qemu-xen.

We always had an empty cdrom and I don't see why we should remove it. If
cd-insert doesn't work, it's a bug and should be fixed.

Supporting spice in PV guests would be hard, because spice needs QXL
that is a PCI device. PV guests don't have a PCI bus. Of course if
somebody did the work to make QXL and spice work with PV guests I would
be happy to accept it.

I agree that we should keep improving upstream QEMU, however removing
qemu-traditional is not going to be easy because it's needed for
compatibility when a guest started with qemu-traditional is
live-migrated to a new system. But we can make sure that this remains
the only use case for it.

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