On Tue, 2011-02-01 at 23:24 +0200, Michael S. Tsirkin wrote:

My theory is that the issue is not signalling.
Rather, our queue fills up, then host handles
one packet and sends an interrupt, and we
immediately wake the queue. So the vq
once it gets full, stays full.

From the printk debugging output, it might not be exactly the case. The

ring gets full, run a bit, then gets full, then run a bit, then full...

If you try my patch with bufs threshold set to e.g.
half the vq, what we will do is send interrupt after we have processed
half the vq.  So host has half the vq to go, and guest has half the vq
to fill.

See?

I am cleaning up my set up to run your patch ...

Shirley