On Wed, Nov 23, 2011 at 4:01 PM, Gerd Hoffmann <kra...@redhat.com> wrote: > 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.
It may be unrelated :). This is the only error message I saw in the logs. >> 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. Okay. The audio device is designed to fill a 288 byte iso buffer every millisecond, although applications typically use larger power-of-2 buffer sizes. > For starter try a higher number of buffers (isobufs property). > Also make sure you enable the vnc thread (unless you have already). Thanks, I'll try this. Stefan
