[vfio-users] Radeon R9 290, stuttering audio over HDMI with MSI enabled

[Tmplt]

Having spent some hours (unsucessfully) to get stutter-free audio via
Pulseaudio (and ALSA) have left me with the options of either dual
booting or letting dedicated hardware handle the audio, which I can then
mix together into a single output.

However, passing only the GPU as a soundcard and listening to the audio
via my monitor's headphone jack, there is some noticable audio
stuttering. While only noticable when running some more heavier games
(e.g. Battlefield 1), I'm guessing this shouldn't be the case, and that
I've configured something incorrectly. Especially since I've enabled
MSIs for both the GPU and the GPUs audio device.

Here is what my system is:
CPU:  i5-6600k @ stock
MOBO: ASUS Z170-A
RAM:  16GB DDR4 at 2133Mhz (I think, could be 1600)
GPU:  ASUS R9 290 (for the VM; reference card)

HOST OS:  Arch Linux
GUEST OS: Windows 8.1

I run my VM via qemu (2.8.0) and libvirt (2.4.0).

When Windows was installed it automatically enabled MSI for the GPU. I
manually enabled it for the audio device, rebooted, and confirmed that
they both appeared below the IRQ drop-down in the device manager.

It can be worth of note that I flashed my card with a UEFI-bios some
time ago so that it got passed-through without issue. I can't recall
whether this was required for my qemu config at the time or if a
non-UEFI card can't be passed through. I'm also not sure if both BIOSes
(there is a switch to toggle between the two on my card) are overwritten
during the flash, or just the current one. Either case, the topical
issue is present on both settings.

Here follows my libvirt .xml-config:
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>windows</name>
  <uuid>e3ec8ec6-087d-443a-8899-fab99b9251f2</uuid>
  <memory unit='KiB'>8388608</memory>
  <currentMemory unit='KiB'>8388608</currentMemory>
  <vcpu placement='static'>4</vcpu>
  <iothreads>2</iothreads>
  <cputune>
    <vcpupin vcpu='0' cpuset='0'/>
    <vcpupin vcpu='1' cpuset='1'/>
    <vcpupin vcpu='2' cpuset='2'/>
    <vcpupin vcpu='3' cpuset='3'/>
  </cputune>
  <os>
    <type arch='x86_64' machine='pc-i440fx-2.7'>hvm</type>
    <loader readonly='yes'
type='pflash'>/usr/share/ovmf/x64/ovmf_x64.bin</loader>
    <nvram>/var/lib/libvirt/qemu/nvram/windows_VARS.fd</nvram>
    <bootmenu enable='no'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <hyperv>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
    </hyperv>
    <vmport state='off'/>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='4' threads='1'/>
  </cpu>
  <clock offset='localtime'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
    <timer name='hypervclock' present='yes'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <pm>
    <suspend-to-mem enabled='no'/>
    <suspend-to-disk enabled='no'/>
  </pm>
  <devices>
    <emulator>/usr/sbin/qemu-system-x86_64</emulator>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='threads'
iothread='1'/>
      <source dev='/dev/sda'/>
      <target dev='vdb' bus='virtio'/>
      <boot order='3'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='threads'
iothread='2'/>
      <source dev='/dev/sde2'/>
      <target dev='vdc' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0c'
function='0x0'/>
    </disk>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='virtio-serial' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
    </controller>
    <controller type='usb' index='0' model='piix3-uhci'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01'
function='0x2'/>
    </controller>
    <interface type='network'>
      <mac address='52:54:00:20:63:3a'/>
      <source network='default'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
    </interface>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x09'
function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x02' slot='0x00' function='0x1'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03'
function='0x0'/>
    </hostdev>
    <memballoon model='none'/>
  </devices>
  <qemu:commandline>
    <qemu:arg value='-object'/>
    <qemu:arg
value='input-linux,id=kbd,evdev=/dev/input/by-id/usb-04d9_USB_Keyboard-event-kbd,grab_all=yes,repeat=yes'/>
    <qemu:arg value='-object'/>
    <qemu:arg
value='input-linux,id=mouse,evdev=/dev/input/by-id/usb-La-VIEW_CO._QPAD_Gaming_Mouse-event-mouse'/>
    <qemu:arg value='-object'/>
    <qemu:arg
value='input-linux,id=mouse-thumb,evdev=/dev/input/by-id/usb-La-VIEW_CO._QPAD_Gaming_Mouse-if01-event-kbd'/>
  </qemu:commandline>
</domain>

Have I done anything wrong here?

Cheers,
  Tmplt.