[vfio-users] VGA Passthrough limitations?

[thibaut noah]

I'm thinking same thing as heroes of the storm, msrs spamming ?

2016-05-18 14:27 GMT+02:00 Andrei Grigore <andrei.grg at gmail.com>:

> Dear all,
>
> I have this very strange issue that I can not understand:
>
> Everything works flawlessly or even better than bare metal. ...thing is,
> if I enable stereoscopic 3d vision (nvidia) in game, the performance drops
> to unplayable. The reason for that are CPU /RAM intensive elements such as
> view distances. Dropping other graphical elements to the lowest possible
> value makes no difference. This means that the GPU is not the bottleneck.
> Tested this on bare metal and i get around 50 fps with everything maxed
> out. With VGA passthrough I barely get 20. Disabling 3d vision boosts
> everything to 60 fps.
>
> The entire 3d vision sensor usb bus is passed through as well. I am
> running just this VM with 8/8 cores of a fx-8230 cpu with 12 gb of ram. The
> cpu is passed with host-passthrough. I am even using your latest patch and
> had enabled hyperv extensions with nvidia GPUs.
>
> The VM is installed clean with nothing but the games in it. As said using
> the same drivers on a bare metal windows works flawlessly.
>
> I cannot understand where the bottleneck is. CPU usage is not even close
> to 100%, plenty of ram left and not even 1MB of swap is made.
>
> I don't even know where to seek the problem. What can cause such a massive
> fps drop? Is there any bandtwidth limit that caps the 2x rendering needed
> for 3d vision?
>
> Many thanks,
> Andrei.
>
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