Wondering about cirris and stdvga

[Dario Faggioli <dario.faggioli@citrix.com>]

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Sending again, this time, with Anthony's and xen-devel address spelled
right. Sorry!! :-(
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Hello to you, various pseudo-random people,

It's not my field of expertise, so bear with me, at least a little bit
(and, Konrad, you help me, or there will be consequences! :-D)

So, I and Konrad recently discovered --while testing the about to be
released Fedora 25 as a Xen guest-- that the Cirrus emulated graphic
card that we consume from QEMU for HVM guests is broken on Wayland.

We just discovered it because Fedora 25 uses Wayland by default, but it
appears not to be something new:

https://bugzilla.redhat.com/show_bug.cgi?id=1227770

And at least from what we see in that bugreport, not much has happened
so far.

Using "vga='stdvga'" in the config file, or even "vga='qxl'" make
things work again. Disabling Wayland in the guest also works (i.e., if
not using Wayland, Cirrus is ok). And that's what made us think that
it's probably a Wayland issue.

I've tried the same on KVM, and the situation is identical
(Cirrus+Wayland=breaks, whatever-else+Wayland=works,
Cirrus+Xorg=works).

I've also read around that these days, e.g., stdvga is at least as good
as cirrus, performance wise, that cirrus is broken and impossible to
fix (because it is the hardware that it's emulating that was broken),
that stdvga enables better screen resolution in guests, etc.

I'm not sure about these claims, in particular the performance one, is
probably pretty hard to verify. And as I said, it's not my field.

Still I thought it could be worthwhile to at least bring this up:
should we start to consider changing the default from cirrus to stdvga
(or something else)?

Thanks for your time and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
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Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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