I'm using Xen for some time now with VGA passthrough to a Windows 7 VM. It works incredibly well!
Originally Posted by bulletxt
Yes, it has been a pain to set up, mainly because of my stubborness to use unconfirmed hardware (a Nvidia Quadro 600 for the Windows guest system didn't work, my Quadro 2000 now works perfect) and because of making it work on a distro that hasn't yet seen a how-to on that.
The most important step before embarking on it is to check that the hardware meets the requirements. If it does, it's quite simple.
Here some links to start with:
http://www.overclock.net/t/1205216/g...irtual-machine - good tutorial with a long thread and a wealth of information.
http://forums.linuxmint.com/viewtopic.php?f=42&t=112013 - can't judge my own tutorial, but I hope it helps. It should work likewise (or very similar) under Ubuntu. There is some more info in posts following the tutorial, to tweak stuff.
I totally disagree with Xen being more difficult than kvm. It's perhaps not the easiest of hypervisors, but at least it offers a wealth of documentation. KVM on the other hand is a disaster! Perhaps the hype about KVM is because it's the new kid on the block?
Originally Posted by Mathias
When I started out on my quest for VGA passthrough I was set on KVM and almost dismissed Xen. One reason for dismissing Xen was the wealth of documentation which at that time I misinterpreted for Xen being complex. Yes, Xen offers multiple options and tools to reach the same goal (see below), but the fact that there is a lot of documentation is a real asset. The other reason for almost dismissing it was some reports here on Phoronix about poor performance. Boy, am I glad I dug a little deeper into that. It turned out there was some bug (which is long fixed now), but for most of these tests here I don't really see a point other than proofing that KVM is getting closer to Xen in some areas. As to real-life performance: you need to see it to believe it.
Some of the tests here are a bit questionable, for example comparing KVM and Xen with Linux HVM guests. The only reason I use Linux HVM guests from time to time is to check out a distro, but I don't expect performance miracles. Most times a Linux PV guest will perform better since it has access to the hardware drivers of the hypervisor and doesn't need an emulation layer. Linux HVM guest performance can be improved by using PVHVM drivers and I believe (or hope) they have been used by Phoronix. With Xen offering several options, it's really necessary to be precise about a test setup. Newcomers would certainly be helped with an explanation of why one option was chosen over another.
Recently Xen developers have rolled out a lot of improvements with kernel 3.x and Xen 4.x. Now that Xen 4.2 stable is out (but not yet included in the major distros) things should become even easier, with better support for more hardware. Xen 4.2 also does away with a lot of accumulated code and layers that are not really helping it. The new xl toolstack replaces xm and xend (among others), and is more efficient.
It is true there are probably not many KVM users who have accomplished VGA passthrough, though it's been done. But there are quite many people already doing Xen VGA passthrough.
From a practical perspective, I am using Xen and Windows with VGA/PCI passthrough for semi-professional photography work. When I compare my Xen system with native Windows 7 installs on similar hardware owned by friends, I find even less reasons to look back. If you have the right hardware, I would go for it any second.
nVidia can be tricky or outright impossible to pass through. I am using a nVidia Quadro 2000 for pass through and it works perfect, BUT this card along with some more expensive ones are the only nVidia cards that officially support what they call "multi-OS" which is exactly what's needed for it to work.
Originally Posted by DeepDayze
It has been reported that some other (non-professional) nVidia cards can actually be passed through, so it's best to search. Look here http://wiki.xen.org/wiki/Xen_VGA_Pas...ested_Adapters and here http://www.overclock.net/t/1307834/x...phics-adapters for a start.
If your nVidia card is not listed, but you are adventurous, you might find a solution here: http://www.davidgis.fr/blog/index.ph...a-pass-through. Note that some of the patches listed there should already be available in the 4.2 stable hypervisor.
For instructions on how to get VGA passthrough working, see my post #11 above.