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xen-users
Re: [Xen-users] Xen handling of graphics card
Petersson, Mats wrote:
There's two distinct possibilities for graphics improvement using the
VNC model:
<snip>
2. A more intelligent and modern form of graphics commands.
QEMU currently does not utilitize any of the cirrus 2d graphics
acceleration operations for VNC. This could be a pretty big performance
improvement for VNC since cirrus supports blt operations (VNC CopyRect)
and fill operations (various subtypes of hextile, tight, or zrle
encodings). CopyRect has a pretty noticable performance improvement
since window dragging becomes noticably better.
The biggest performance enhancement for VNC (IMO) is cursor offloading
and unfortunately, cirrus doesn't help us much here. It only provides
acceleration for a black/white cursor of a finite size.
Upgrading the VGA driver to a newer chipset might help here except that
that's probably an awful lot of work.
A non-VNC model:
You could also, conceivably, have a situation where the graphics
controller is directly handled by either Dom0 or the Guest, using a
"para-virtualized" driver, where the driver is Xen-aware, and has some
sort of "agreement" of how to share the hardware.
http://wiki.xensource.com/xenwiki/VirtualFramebuffer
I currently only have a Linux domU driver (no Windows support). I don't
know much at all about Windows but a Windows driver shouldn't be that
much more difficult than the Linux one was.
The Linux paravirtualization side is pretty interesting here.
Currently, I'm able to use the X fbdev driver. I have some local
(hacky) patches that add a ARGB cursor to the fbdev driver which would
solve the VNC cursor problem pretty well (at least for Linux).
I'm still working on integrating a write-trapping update idea from Gerd
Knorr although a patch should show up very soon that includes that.
Regards,
Anthony Liguoir
This would require a
hypervisor level locking/sharing mechanism so that the driver of one
guest can do the necessary hardware access without being "disturbed" by
some other guest trying to access some shared resource.
This is however, a BIG job, even for a pretty simple graphics card,
there'd need to be quite a lot of work. For COMPLEX graphics cards, the
driver is HUGE, and although the actual accesses to the hardware are
probably few and pretty centralized, the work to understand the driver,
modify it in a safe way, and getting it to work reliably (and
effectively) across multiple OS architectures is not easy.
--
Mats
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