Re: Wondering about cirris and stdvga

From: "Pasi Kärkkäinen" <pasik@iki.fi>
To: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>,
	Paul Durrant <Paul.Durrant@citrix.com>,
	"anthony.perard" <anthony.perard@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Roger Pau Monne <roger.paumonne@citrix.com>
Subject: Re: Wondering about cirris and stdvga
Date: Sat, 19 Nov 2016 12:56:41 +0200	[thread overview]
Message-ID: <20161119105641.GL28824@reaktio.net> (raw)
In-Reply-To: <1479492255.3832.52.camel@citrix.com>

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".

2) It'd good to create an upstream Wayland bugreport and investigate more about why cirrus is broken with Wayland.

3) It'd be good to have Xen HVM with "qxl" tested by OSStest aswell..

> Thanks for your time and Regards,
> Dario

Thanks,

-- Pasi

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