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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

-------- Forwarded Message --------
From: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Subject: Re: Wondering about cirris and stdvga
Date: Fri, 18 Nov 2016 11:26:07 -0800
Mailer: Alpine 2.10 (DEB 1266 2009-07-14)
Message-Id: <alpine.DEB.2.10.1611181123310.3290@sstabellini-ThinkPad-
X260>

On Fri, 18 Nov 2016, Konrad Rzeszutek Wilk wrote:
> 
> On Fri, Nov 18, 2016 at 06:08:57PM +0000, Ian Jackson wrote:
> > 
> > Dario Faggioli writes ("Wondering about cirris and stdvga"):
> > > 
> > > I've also read around that these days, e.g., stdvga is at least
> > > as good
> > > as cirrus,
> > 
> > You pasted a url in IRC which seemed to be arguing that but
> > actually
> > failed to make the case.  (Sorry, don't have it to hand now.)
> 
> This one?
> https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harm
> ful/
> > 
> > 
> > > 
> > > 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.
> > 
> > I wouldn't want to change the default just because Wayland is
> > broken.
> > Wayland should be fixed.
> 
> 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.
 
I am no Xorg maintainer but back in the XenClient days we did some perf
analysis and it turned out that the bitblt operations supported by
Cirrus are actually very slow to emulate in QEMU. stdvga is faster
because it doesn't support them. In addition stdvga supports higher
resolutions: as high as the videoram assigned to the guest can support,
while cirrus is limited.
-- 
<<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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