[Xen-users] Multiple VMs VGA Passthrough Success Report

[Gordan Bobic <gordan@xxxxxxxxxx>]

I just wanted to drop a note to say that I have managed to get VGA 
passthrough working with multiple cards and domUs.
The cards I am using are quasi Quadro 5000 (modified GTX470) and quasi 
Quadro 6000 (modified GTX480). (Here is an older article about modified 
GTS450 modified to Quadro 2000 if anyone is interested:
http://www.altechnative.net/2013/06/23/nvidia-cards-geforce-quadro-and-geforce-modified-into-a-quadro-for-virtualized-gaming/ 
)
This succeeded despite all the PCIe slots being behind NF200 bridges 
without ACS support.
I now have two VMs with VGA passthrough running, with one card passed 
through to each one. The OS is EL6, and I am using Xen packages and 
kernel from the CRC repository.
What is strange, however, is that whereas I had issues with a single VM 
crashing on reboot with VGA passthrough (and usually taking the host 
down with it), with two VMs running, I seem to be able to reboot them 
dozens of times without any crashes, problems, or performance 
degradation (yes, rebooting VMs with VGA passthrough without rebooting 
the host and there appears to be no effect on performance with Nvidia 
Quadro cards). This new found stability could be down to some of the PCI 
changes, though, with different USB controllers being passed through, 
and NIC being bridged rather than PCI passthrough since there are now 
two domUs that have to share it, so it is possible that the PCI memory 
stomp I am suspecting to be the root cause is getting coincidentally 
avoided (not that I'm complaining!).
I'm happy to share more details on and off list if anybody is interested.

Gordan

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