[Xen-users] Xen on the desktop with VGA passthrough -- problems, concerns and clarification needed

["Marek Kaszycki" <marek@xxxxxxxxxxx>]

Hi everyone!

I am sorry if my question has already been answered, I can't seem to find  
the exact and complete reply to my concerns. After reading through the  
howtos, I can see some bits are missing -- apparently some magic happens  
between one guide and the next, and the magic does not seem to work for me.
Let's begin with my configuration first and move on to what I would like  
to achieve next.
1. Gigabyte GA-890FXA-UD5 (AMD 890FX chipset with enabled IOMMU support,  
two LAN ports)
2. AMD Phenom 2 1055T CPU
3. 8 GB RAM
4. AMD 5850 GPU
5. 60 GB OCZ Vertex II SSD
6. 4x1 TB HDDs (complex 4-md RAID setup)

I'm fairly confident the above configuration is flexible enough. I am able  
to dedicate a separate partition on the SSD for the system, as well as  
another partition on the RAID for the data. I can spare up to 6 gigabytes  
(3 for the 32-bit version) and 4-5 cores for Windows, leaving Linux with  
at least 2 gigabytes and 1 core for housekeeping.

I would like to stay with Linux in dom0 for day-to-day work and web, while  
at the same time being able to boot Windows (XP and/or 7) to play games. I  
have already tried to use wine and VirtualBox (with its Direct3D drivers)  
for that purpose, but the solution is unacceptable for various reasons,  
mostly the performance impact and graphics artefacts in a lot of titles  
with anything but basic graphics.
I figure PCI passthrough would address both the performance issue and the  
graphics artifacts, while allowing me to stay away from dual booting the  
system. I would like to use 2.35 kernel or later (the main reason is that  
it safely supports most, if not all, the features of the CPU, including  
Turbo), preferably 2.36 (I did note the huge performance loss when there  
is a lot of I/O pending, which 2.36 apparently fixed in my case).
Now, I've got several questions of how I go about that.
1. Which distribution would you recommend for the host OS? I am  
comfortable with changing the distro if it suits dom0 usage better. I am  
running Debian at the moment, but I'm not blindly loyal, especially since  
I can't expect the latest kernel and since there are some tricks with  
running Debian  
(http://blog.xen.org/index.php/2009/12/15/support-to-be-removed-from-debian-squeeze-call-for-volunteers/)  
-- I see there's been no follow-up to that, making me wary of using  
Debian. Additionally, there apparently are some reservations about running  
Xen dom0 with proprietary graphics drivers, which coupled with problems  
running the system with open drivers (more on that below) would make it a  
tedious exercise.
2. As I understand from VGA passthrough page  
(http://wiki.xensource.com/xenwiki/XenVGAPassthrough), the primary adapter  
gets passed through to the guest OS. Please correct me if I'm wrong, but  
as I understand it, the dom0 desktop gets frozen and the HVM guest assumes  
complete control of the GPU, leaving the dom0 unable to use the VGA  
adapter while the HVM guest is running? This is fully acceptable for me,  
but please let me know if it works differently, e.g., dom0 cannot have the  
desktop launched (this would make it not much different from dual booting  
in my case, where Linux takes less than half a minute from boot to  
desktop).
3. What exact steps should I take to install, configure and then run the  
OS? I became stuck in Debian after being unable to run any kernel with  
Xen. Due to problems with running the open Radeon driver under 64 bits in  
Debian (this is really frustrating, the picture was unviewable: distorted  
and full of artefacts) I have to use the closed fglrx driver. Curiously  
enough, this didn't happen under Ubuntu, where the open driver worked  
properly out of the box, but Ubuntu did mangle my RAID setup and I've  
become wary of Ubuntu as a result. 2.26 and 2.32 included with the  
distribution failed to run the desktop with it, though (and the system  
froze at this point), while 2.37 failed to start to boot completely.  
Bearing this in mind, I want to be prepared for the likely disappointment  
in initial test runs.
4. I am already using Virtualbox for light Windows (XP) usage (e.g. some  
flash+shockwave, light gaming, basically whatever works acceptably under  
VB) and some OS testing. I'm fairly confident I'm going to continue using  
VB to that end and only use Xen guest to run Windows 7 for 'hardcore'  
gaming. To that end, I'm planning the Windows 7 installation to be light  
(I can go either 32 or 64 bit) and will likely keep it unpatched (since  
I'm going to restore from backup in case of any severe fault).

Many thanks in advance!
Marek

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