[vfio-users] Stuttering audio when passing through USB controller

Fri Feb 3 19:53:03 UTC 2017

I saw on an older thread here that passing a USB controller through and
using a USB soundcard through it solved that users audio issues. I tried
that myself by adding

    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0000' bus='0x00' slot='0x14' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
    </hostdev>

to the .xml-file, but I can still hear frequent audio stutters akin to
my quoted thread. Am I passing the controller incorrectly? The device
I'm trying to play through is a FiiO e10k DAC which works without issue
on the host and on bare-metal Windows 8.1.

Here follows my windows-pciusb.xml:

<domain type='kvm'>
  <name>windows-pciusb</name>
  <uuid>7353cd48-34ee-4a26-b8ac-7c5d1735777a</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='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01'
function='0x1'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
    </controller>
    <interface type='network'>
      <mac address='52:54:00:0d:18:bf'/>
      <source network='default'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03'
function='0x0'/>
    </interface>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <sound model='ich6'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
    </sound>
    <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='0x0a'
function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0b'
function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x045e'/>
        <product id='0x028e'/>
      </source>
      <address type='usb' bus='0' port='1'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0000' bus='0x00' slot='0x14' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
    </hostdev>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07'
function='0x0'/>
    </memballoon>
  </devices>
</domain>

lsusb reports that everything goes to the same, single USB controller,
which is what I pass. Could that be the issue? I'm qouting my last
thread in case any info there helps.

Thanks in advance!

On 01/29/2017 12:38 AM, Tmplt wrote:
> I forgot to mention: I'm using the linux-vfio kernel, v4.8.13, and my
> only kernel options are intel_iommu=on and pcie_acs_override=downstream.
> 
> On 01/28/2017 06:13 AM, Tmplt wrote:
>> 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.