[PATCH 02/12] kvm: qemu: Remove virtio_net tx ring-full heuristic

[Mark McLoughlin <markmc@redhat.com>]

virtio_net tries to guess when it has received a tx
notification from the guest whether it indicates that the
guest has no more room in the tx ring and it should
immediately flush the queued buffers.

The heuristic is based on the fact that there are 128
buffer entries in the ring and each packet uses 2 buffers
(i.e. the virtio_net_hdr and the packet's linear data).

Using GSO or increasing the size of the rings will break
that heuristic, so let's remove it and assume that any
notification from the guest after we've disabled
notifications indicates that we should flush our buffers.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
---
 qemu/hw/virtio-net.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
index 3a39c8f..b001475 100644
--- a/qemu/hw/virtio-net.c
+++ b/qemu/hw/virtio-net.c
@@ -175,8 +175,7 @@ static void virtio_net_handle_tx(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIONet *n = to_virtio_net(vdev);
 
-    if (n->tx_timer_active &&
-	(vq->vring.avail->idx - vq->last_avail_idx) == 64) {
+    if (n->tx_timer_active) {
 	vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;
 	qemu_del_timer(n->tx_timer);
 	n->tx_timer_active = 0;
-- 
1.5.4.1