Re: [Qemu-devel] husb: out of buffers for iso stream

[Gerd Hoffmann <kraxel@redhat.com>]

On 11/19/11 20:40, Stefan Hajnoczi wrote:
> I have a Windows 7 VM running a sound driver for a passthrough USB
> host device.  The driver submits iso in and out urbs to do audio
> capture and playback at the same time.
> 
> Audacity running inside the guest freezes and does not record audio
> unless I move the mouse.  Somehow it seems USB iso urbs aren't being
> pumped unless I keep moving the mouse.  The VM is using VNC.

I have no idea how moving the mouse could possibly help here.

> Checking the QEMU stderr logs I see many occurrences of "husb: out of
> buffers for iso stream".  Perhaps this message is enough to pinpoint
> the problem?

It means the number of buffers in flight (on the host side) went down to
zero, i.e. the stream is interrupted.

usb-host maintains a set of buffers (four by default) per iso endpoint
to keep the constant data flow up, i.e. pass one buffer to the guest
while the host fills the next one.  Now the host has no more buffers to
fill.  Most likely usb-host sits on a bunch of full buffers which it
hasn't passed to the guest yet.

For starter try a higher number of buffers (isobufs property).
Also make sure you enable the vnc thread (unless you have already).

cheers,
  Gerd