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[Xen-devel] [Fwd: Re: Wondering about cirris and stdvga]

-------- Forwarded Message --------
From: Adam Jackson <ajax@xxxxxxxxxx>
Subject: Re: Wondering about cirris and stdvga
Date: Fri, 18 Nov 2016 15:19:08 -0500
Message-Id: <1479500348.16973.1.camel@xxxxxxxxxx>

On Fri, 2016-11-18 at 13:32 -0500, Konrad Rzeszutek Wilk wrote:
> On Fri, Nov 18, 2016 at 06:08:57PM +0000, Ian Jackson wrote:
> > 
> > 
> > > 
> > > 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.
> > 
> > The "broken and impossible to fix" sounds like FUD TBH.

The "fear" bit, perhaps; it is arguably frightening that we continue to
emulate in 2016 a chip that was inadequate in 1996. In my opinion about
cirrus being broken, however, I am neither uncertain nor in doubt.

> > 
> > I wouldn't want to change the default just because Wayland is
> > broken.
> > Wayland should be fixed.

You should want to change the default because it is bad, even for X.

> CCing Adam Jackson who I hope can enlighten us on the technical
> parts of Xorg.
> I am really interested in knowing the technical merits
> of the stdvga vs cirrus and I hope to understand what the Xorg
> maintainer(s) have in mind.

The cirrus chip that qemu happens to emulate is trash. It can't do
32bpp, it can't do modes larger than 2048 wide, it can't do more than
4M of VRAM. We could of course extend the qemu emulation to be more
capable; doing so would require updating every guest to know about
these enhancements, though.

stdvga, as it has none of the above problems, is _today_ uniformly
better than cirrus. It is still perhaps less awesome than one would
like (no idea how multihead is expected to work for example), but there
is no world in which stdvga is worse than cirrus.

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

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