Re: [Xen-devel] PCI and VGA Passthrough regressions on Xen 4.4.1 vs 4.3.2‏

[Zir Blazer <zir_blazer@xxxxxxxxxxx>]

A few more things, through this topic seems to have been forgotten already:


- When you mentioned originally to test with another hvmloader, I misunderstood 
and used Xen 4.3.2 hvmloader in Xen 4.4.1, when what you said was the other way 
around. Still, doesn't seem to be worth to retest this.


- I missed to mention this last time, but X10SAT Firmware saves SMBIOS events 
on the NVRAM. When VGA Passthrough fails, it logs two consecutive errors at the 
same time with ErrorCode 0x0A Bus00(DevFn08). I didn't paid attention to WHEN 
exactly it happens, if the first time I try passthrough and the DomU BSODs, or 
the second time when the whole Dom0 freezes.


- Teo En Ming mentioned that he got VGA Passthrough working in Xen 4.4.1 
WITHOUT using qemu-xen-traditional. After making that change in the DomU config 
file, I tried disabling the Cirrus GPU and rebooting, but the DomU BSODed at 
boot complaining about ATI Drivers. I should have done so on a brand new DomU, 
cause changing from qemu-xen-traditional to qemu-xen makes Windows want to 
reinstall lots of devices. The best chance would be to download Ubuntu ISO and 
use their packages, just to make sure I can repeat his exact steps. Didn't 
really spend time seriously trying to get this one working.



So far, for my "production" system (Better said, my everyday gaming Windows 
DomU), the new Xen 4.3.3 seems that will happily get the job done, through not 
having the latests and greatest doesn't satisfies me. I managed to get it 
working with a DomU with WXP x64, PCI and VGA Passthrough (With the full 
Catalyst suite installed), a LVM partition instead of file based storage, and a 
whopping 24 GB of RAM. I didn't toyed around a lot but seems to be working 
nicely (Hear about tons of performance issues regarding 4 GB+ RAM and VGA 
Passthrough). Will have to stress test it a bit, but it seems quite promising 
as replacement for my 1 year old WXP SP3 DomU. Modern RAM requeriments are what 
killed WXP SP3 for me, I was hitting the 3.5 GiB wall too often, and being file 
backed it had quite low I/O performance.


Is sad that there isn't enough dev manpower to at least maintain a base 
compatibility level for passthrough, it seems that every user gets crazily 
different results based on Hardware, Xen version, Linux distro, toolstack, etc. 
What worked flawlessly on a Xen version could be completely messed up in the 
next one. This means that once you get it working once, you just stop upgrading 
to make sure that it doesn't breaks. Even then, nothing beats Xen VGA 
Passthrough when it works.                                          
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