[Qemu-devel] FreeBSD guest and Linux host with EVENT_IDX feature

[Vince Hurrell]

Hello,

I've been having trouble when enabling the EVENT_IDX feature in the
virtio-net guest FreeBSD driver.  The feature enables fine, but traffic
through the virtual interface (perceived from the guest side) stops
relatively quickly after starting the KVM instance on the host side.

I'm using multi-queue on the virtual NIC as well with vhost-net.  If I
disable EVENT_IDX then everything works fine, but I need the performance
benefit of EVENT_IDX.

I've heavily instrumented the guest driver, but I've been unable to find
the problem.  One thing I've noticed is the value of
"vq->vq_ring.used->ring[vq->vq_ring.num].id" in the guest driver always
increases.

I've started instrumenting the notification code on the host side as well,
but I'm afraid I'm heading down a very confusing rabbit hole.

I'm hoping someone here may be able to give me some useful information
where best to be looking if I'm not already looking in the correct spot :)

Thanks,

Vince