Re: Wondering about cirris and stdvga

[Stefano Stabellini <sstabellini@kernel.org>]

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On Mon, 21 Nov 2016, Paul Durrant wrote:
> > -----Original Message-----
> > From: Pasi Kärkkäinen [mailto:pasik@iki.fi]
> > Sent: 19 November 2016 10:57
> > To: Dario Faggioli <dario.faggioli@citrix.com>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Paul Durrant
> > <Paul.Durrant@citrix.com>; Anthony Perard <anthony.perard@citrix.com>;
> > xen-devel <xen-devel@lists.xenproject.org>; Stefano Stabellini
> > <sstabellini@kernel.org>; Ian Jackson <Ian.Jackson@citrix.com>; Roger Pau
> > Monne <roger.pau@citrix.com>
> > Subject: Re: [Xen-devel] Wondering about cirris and stdvga
> > 
> > On Fri, Nov 18, 2016 at 07:04:15PM +0100, Dario Faggioli wrote:
> > > Sending again, this time, with Anthony's and xen-devel address spelled
> > > right. Sorry!! :-(
> > > -------------------------------------------
> > > 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)?
> > >
> > 
> > There's multiple things here..
> > 
> > 1) Yes, +1, let's change the Xen HVM default to "stdvga".
> > 
> 
> In general std-vga also gets a +1 from me, but I have recently found that a Windows Server 2008 guest does not boot (ar at least the display freezes on boot) when using std-vga with QEMU trad but everything is fine with Cirrus... so probably worth making the default dependent on which QEMU is being used. Never had any issues with std-vga on upstream QEMU.

In all fairness, I think it's worth mentioning that the original reason
for defaulting to Cirrus was that Windows XP wasn't able to boot on
stdvga either.

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