On 12/04/2017 03:27 PM, Ladi Prosek wrote:
On Mon, Dec 4, 2017 at 3:08 PM, Maxime Coquelin
<maxime.coque...@redhat.com> wrote:
Having QEMU started with mq=on but guest driver not negotiating
VIRTIO_NET_F_MQ feature ends up in the vhost device to never
start. Indeed, more queues are created in the vhost backend than
configured.
Guest drivers known to not advertise the VIRTIO_NET_F_MQ feature are
iPXE and OVMF Virtio-net drivers.
Queues are created because before starting the guest, QEMU sends
VHOST_USER_SET_VRING_CALL requests for all queues declared in QEMU
command line. Also, once Virtio features negotiated, QEMU sends
VHOST_USER_SET_VRING_ENABLE requests to disable all but the first
queue pair.
This series fixes this by destroying all but first queue pair in
the backend if VIRTIO_NET_F_MQ isn't negotiated.
The destroyed queue pairs will be re-created when an MQ-enabled driver
takes over later on, though, is that correct?
Correct! When the new driver registers, QEMU sends
VHOST_USER_SET_VRING_ENABLE requests to all queues in order to enable
only the first queue pair, disabling all others queue pairs.
In QEMU, see virtio_net_set_queues() in hw/net/virtio-net.c
iPXE and OVMF virtio-net drivers will typically not be the last ones
driving the device. They will likely load an OS equipped with a driver
that negotiates the MQ feature. Thanks!
Maxime
