[vfio-users] USB ASIO DAC buffer underruns on Windows guest

[George Amanakis]

I am using a Behringer UMC204HD as a USB ASIO DAC to record
guitars/voice and was noticing some underruns on a Win10 guest. Host is
a Xeon E5-2667v2, on archlinux 4.19.12.

Two things helped a great deal for me:
1) setting the cpu gorvernor to performance on the host
2) assigning the IRQ of the USB controller (which the DAC sits on) to
one of the cores that are passed to the guest. You cannot do this with
libvirt, it has to be done on the host with a script. E.g. if you pass
cpus 1-7,9-15 on the host to the guest:

----------8<----------
for i in $(grep vfio /proc/interrupts \
	| awk '{print $1}' | sed -e 's/://'); do
	echo 1-7,9-15 | tee /proc/irq/$i/smp_affinity_list
done
----------8<----------

Best,
George