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Re: [Xen-devel] virtualGraphicCards

To: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] virtualGraphicCards
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Wed, 07 Sep 2005 16:15:14 -0500
Cc: "Retzki, Sascha \[Xplain\]" <sascha.retzki@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Daniel Hulme <dh286@xxxxxxxxx>
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Mark Williamson wrote:

X is not the center of this world. If it is, something is wrong.
I think VESA, VGA, other (better, newer) protocols are way better. They
are more generic, and thus *can* be supported by other Operating
Systems. Despite that X is on another "layer" (layer as in OSI, just for
graphics cards ;-))...

The intention isn't to limit ourselves to using X. The plan would be to define the "Xen video protocol" then write a driver to make X talk it. Anyone else could port their system to talk to it too.

I'd be inclined to implement the Xen video device in the guest kernel, then get X to use that (as it can for existing framebuffer drivers).
The problem with framebuffers is that you lose higher level primatives (like blitting, rect fills, moves). Modern remote display protocols (NX, VNC) are optimized to take advantage of these higher level primatives.

The thing that really gets you is that modern environments draw software cursors a lot. Paying a round trip for every cursor movement makes the mouse visibly laggy. Even qemu has this problem (when you export it's display over VNC) as the cirrus hardware cursor is not often used (as it's only black and white and fixed size).

I'm becoming fonder of the idea of virtualizing at a much higher level (perhaps even at the OpenGL level). I'm not sure how we bridge this effectively to fully virtualized domains either.


Anthony Liguori


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