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

Il 05/09/2013 13:23, Stefano Stabellini ha scritto:
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
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
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
and I think that probably need to revise the definition of the devices
avoid empty and unusable ones and to do everything as best as possible
with possibly reviewing qemu side).
Another good thing is also consider pv domU case and possible future
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
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
(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
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.

Thanks for reply.

About qemu default empty and unusable floppy and cdrom I have already reply at start of year that qemu traditional does not have them. The tests were with xl only if I remember good, now I checked also on old production server with xend and qemu traditional. I confirm that hvm domUs is without empty floppy and cdrom also in that case. cd-insert works (tested with xl and upstream qemu). cd-insert does not works only with qemu default empty cdrom because is undefined on xen side.

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