Re: [Xen-users] Anyone using VT-d for GPUs on desktop/workstation?

[Gordan Bobic <gordan@xxxxxxxxxx>]

On Mon, 18 Nov 2013 15:00:50 +0100, "Mgr. Åimon TÃth" <toth@xxxxxxxxxx> 
wrote:
> Is there anyone actually using VT-d for GPU cards?
Yes, many of us.

> From what I understand NVidia is impossible,
Not impossible.

Quadro cards work perfectly.

GeForce cards don't work at all,
courtesy of Nvidia deciding GeForce users should not be
allowed to have this working and making the driver not
cooperate WRT the peculiarities of virtualization.

GeForce cards can be modified into Quadro cards. The
modified GeForce cards work perfectly virtualized. If you
wish to go this route, there are at least two modified
Fermi class (4xx series) GeForce cards on eBay at the moment
going for a fraction of the cost of a real Quadro. I have
used the Fermi class cards extensively, and have had
absolutely no issues with them - they "just work". A
number of people have tried modified Kepler class
cards and the result has been that they generally work
fine for most people but there have on occassion been
reports of minor issues with these.

If you are not too concerned about performance and
you can make do with a GTX480 (i.e. you don't need
to run Crysis at more than 1920x1200 with everything
turned up to max), a modified one of those (into a
Quadro 6000) is probably the most trouble free, most
cost effective way to get a decently performing VGA
passthrough setup going.

If performance is not an issue, a GTS450 modified
into a Quadro 2000 will do nicely.

There was one of each of these on eBay as of this
morning.

> but AMD does work for
> some cards. I would appreciate any hints from people that are 
> actively
> using this technology.
AMD/ATI sort-of works. Poorly. Almost. Anything newer than a HD4xxx
card should "work" in this sense, but you rebooting the domU with
the GPU passed through to will unpredictably result in one of the
following:

1) Host (dom0) crash (complete system lock-up). I find this is
the most common thing to happen, especially when ATI card is
used as the primary console card.

2) domU crash at startup. This could be BSOD, or just the video
output never coming up on either VNC or external monitor.
2.1) If you then try to xl destroy / xl create the same domU
again it will result in 1) every time.

3) Fuzzy lines when dragging windows and massively degraded
performance. I have only ever managed to achieve this
level of "functioning" on a VM reboot with ATI cards that
don't feature auxiliary power input (e.g. HD6450/HD7450).

At the moment, I find ATI cards are NOT a recommendable
solution.

I am using a HD7970 for one of my VMs (modified GTX480s in
all others) but only until I can perfect the hardware
modification on my GTX690, at which point I will be very
glad to see the back of the HD7970. The only reason I
am not using one of the GTX480 cards in place of the
HD7970 is because it wasn't quite managing a perfect
frame rate with everything maxed out on my wife's
2560x1600 monitor in Borderlands 2.

Note that modifying a Kepler class card properly requires
professional skill - soldering 0402 (i.e. 1.5mm along the
longest dimension) components manually takes specialist
equipment unless you are an absolute ninja with a tiny
soldering iron.

Gordan

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