[Xen-users] Audio PCI passthrough issues in a Linux domU

[Arjen <arjenvanweelden@xxxxxxxxx>]

Hi everybody,

I recently started playing with Xen on new hardware with VT-D support to 
set up a "personal cloud". I'm running Xen-4.2.1-r2 with a Gentoo dom0 
and have an issue with on-board audio PCI passthrough to a domU.
I'm setting up my first domU with openSUSE 12.3 and half of my CPU cores 
and memory as a "desktop VM". The USB controller PCI passthrough and 
secondary GPU passthrough (AMD HD7750) work fine. I also tested Ubuntu 
12.04 and 13.04 and they have the same sound issues as openSUSE, and all 
have good audio on the real hardware.
When I do a PCI passthrough of the onboard 00:1b.0 Intel 7/C210 Series 
Chipset HD Audio Controller (rev 04), the hardware is available on the 
domU and detected as snd_hda_intel. Unfortunately, playing sounds 
results in a lot of skipping, repeating and just generic noise. I tried 
removing PulseAudio but Alsa also reports "underruns".
Thinking it might be a timing or performance issue, I tried pinning the 
vcpus, enabling/disabling MSI translation and various sched-credit 
options to no avail. I also tried various snd_hda_intel settings, which 
did not really improve the sound quality. I didn't see any interrupt 
errors on the dom0 or domU.
Has anyone experienced a similar issue? Searching the web and mailing 
lists showed me that other people mostly had other audio issues (as in 
simply no sound) with a Windows domU.
I'm looking for suggestions on how to proceed. What logs should I 
inspect, what settings need checking? Might it be better to use Qemu 
sound emulation? Should I try XCP instead of my current dom0? Can 
someone point me towards more documentation about audio passthrough?
Kind regards, Arjen


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