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

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.


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

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

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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