[vfio-users] I need your help!

[Paige Thompson]

I have been running this setup since October and I have tried since this
time to fix the same issues without any success either in terms of isolating
the problem or fixing it. Here's a lot of details/specs about the setup that
I could think of off-hand to include:

 

https://gist.github.com/cloudkitsch/eefec59233269ace0c9707d0a57e0d5f

 

However before diving into that I want to merely point out that the problem
I'm having is not specific to my graphics configuration which works just
fine except that HDMI audio doesn't work. Not really sure why, maybe because
I'm running Windows 10 N? Don't know. Seems like I remember HDMI audio
working on my Radeon 5770 / Opteron setup that I had VFIO setup on quite a
while ago. 

 

I don't really want HDMI audio either. I have a Yamaha MG10-XU mixer
connected to a USB 3 PCIe card that is also passed through to the guest. It
is a USB audio DAC. The problem I'm having is very specifically with this
mixer however the mixer works just fine on other computers. It doesn't
matter what buffer size I'm using @ 44.1khz (lowest sampling rate) I still
have the same problem which is hard to explain because while I can reproduce
it consistently I can't understand the behavior. Asides from theories, I'm
not really sure where I would start to test. I think that other people
around me are more frustrated with it than I am but I would really like to
first isolate the problem and provide my time (while available) to do what I
can to eliminate the behavior or fix the problem. 

 

I would like to suggest a few reasons why it might be happening, starting
with the fact that the audio will start to skip when the load on the bare
metal host increases or is saturated. This is not always the case, but I
have not found a way to dedicate specific cores to the gust without having
to do something really backwards with numactl to ensure nothing ever touches
the cores that the guest is using. Maybe this is not worth trying anyway? It
seems to suggest that the USB ASIO driver for the MG10-XU has issues with
timing that are impacted by not enough CPU cycles. 

 

It must be more than that though, because it seems to also cut out and skip
relentlessly with mpeg (x264 specifically.) In a lot of games the sound
tends to skip during cinematics and  some high bandwidth movies consistently
cause this problem.

 

However, I can get audio playback up to 192khz FLAC working but the driver
usually crashes after a while and usually requires the whole system to be
pretty idle. The mixer driver doesn't crash like that on other computers.
Both the VGA card and USB card are situated in PCIe slots adjacent to the
same CPU in the NUMA topology however I'm not making any changes to the NUMA
configuration at runtime, I tried without finding that it made any
difference. 

 

I used to have another USB card but that one did the same thing. Everything
else that I could possibly care about works fantastic, including the mouse
responsiveness-I have a whole powered hub of USB devices including an xBox
controller connected to the USB card all of which work great. Games work
really well in 1080p at 120hz. I would try to pass the mixer through VIA USB
redirection (same way I'm doing the corsair PSU) but it wouldn't work and I
don't imagine it would be much better. I've also tried getting my Scarlett
2i2 with it but I have the same kind of problems and it typically doesn't
work for more than 20 seconds at a time.

 

Any thoughts or information you have to share would be appreciated. I'd be
happy to try and debug this some more but I'm completely out of ideas of
where to go. It's an interesting problem to say the least. I have tried a a
lot of different things except those that I can't really try. Please get in
touch if you have any ideas.

 

Thank you, 

 

-Paige

 

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