Re: [Xen-users] ATI VGA Passthrough / Xen 4.2 / Linux 3.8.10

[Gordan Bobic <gordan@xxxxxxxxxx>]

OK, I think I have finally managed to get things to what appears to be 
the average state of unreliability of ATI VGA passthrough (i.e. seems to 
work _most_ of the time after a fresh reboot, but becomes much more hit 
and miss after a VM reboot or two).
I'm probably going to regret saying this when I find that over the next 
week I cannot get it to start up even once, fresh reboot or not, but 
what seems to have made a difference is disabling irq balancing (I'm on 
a dual X5650 machine, 2 CPUs, 6 cores / 12 threads each).
So if you are having similarly difficult time, you might want to try the 
noirqbalance dom0 kernel boot parameter and disable the irqbalance service.
Disclaimer: This is largely based on a gut feeling after a few hours 
testing, I certainly don't think it's definitive, but statistically it 
seems to help.
I have a Quadro 2000 inbound, so I will test with that when it arrives 
next week. The optimist in me very much hoping it will "just work". The 
realist suspects that would be way too easy. Will know for sure one way 
or the other in a few days' time.
Gordan


On 05/05/2013 04:57 PM, Gordan Bobic wrote:
> On 05/05/2013 04:42 PM, Gordan Bobic wrote:
> > This problem continues to drive me nuts - not by it flat out not
> > working, but by working _intermittently_.
> >
> > For the past week, I had not managed to get ATI VGA passthrough to boot
> > up once (BSOD every time). I was tweaking some boot parameters, and at
> > one point it not only booted up without BSOD-ing, it actually managed
> > full screen 3D applications, and completed a full GPU benchmark pass of
> > Crysis!
> >
> > So just to make sure, I did a full shutdown and cold-booted the machine
> > again - BSOD after BSOD after BSOD.
> >
> > Rebooted it again, and now it works again, including full screen 3D
> > switching.
> >
> > One thing I have established is that pci=resource_alignment=<id>;<id>
> > kernel boot parameter makes the machine not boot at all. It looks like
> > it wipes out the NIC by realigning things, and I need the NIC to work
> > because the machine runs on NFS root (and the VM disk is an iSCSI share).
> >
> > Has anybody got any suggestions on how I might debug this any further?
> > It's really quite annoying having this _almost_ working. It also looks
> > like if it works once, it will continue working upon guest restarts.
> Another observation - when it boots up, and I "eject" the ATI card from
> the guest, all that does it switch the guest display briefly to VNC
> primary, followed by slightly corrupted output switching back to the ATI
> card. And it is still responsive after that, I can execute a normal
> shutdown, don't have to do it blind.



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