[PATCH v3 2/2] virtio-net: fix TX timer with tx_burst

[Laurent Vivier <lvivier@redhat.com>]

When virtio_net_flush_tx() reaches the tx_burst value all
the queue is not flushed and nothing restart the timer.

Fix that by doing for TX timer as we do for bottom half TX:
rearming the timer if we find any packet to send during the
virtio_net_flush_tx() call.

Fixes: e3f30488e5f8 ("virtio-net: Limit number of packets sent per TX flush")
Cc: alex.williamson@redhat.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/net/virtio-net.c | 50 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 41 insertions(+), 9 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 1fbf2f3e19a7..b6903aea5450 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2536,14 +2536,19 @@ static void virtio_net_tx_complete(NetClientState *nc, ssize_t len)
 
     virtio_queue_set_notification(q->tx_vq, 1);
     ret = virtio_net_flush_tx(q);
-    if (q->tx_bh && ret >= n->tx_burst) {
+    if (ret >= n->tx_burst) {
         /*
          * the flush has been stopped by tx_burst
          * we will not receive notification for the
          * remainining part, so re-schedule
          */
         virtio_queue_set_notification(q->tx_vq, 0);
-        qemu_bh_schedule(q->tx_bh);
+        if (q->tx_bh) {
+            qemu_bh_schedule(q->tx_bh);
+        } else {
+            timer_mod(q->tx_timer,
+                      qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
+        }
         q->tx_waiting = 1;
     }
 }
@@ -2644,6 +2649,8 @@ drop:
     return num_packets;
 }
 
+static void virtio_net_tx_timer(void *opaque);
+
 static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
@@ -2661,15 +2668,13 @@ static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)
     }
 
     if (q->tx_waiting) {
-        virtio_queue_set_notification(vq, 1);
+        /* We already have queued packets, immediately flush */
         timer_del(q->tx_timer);
-        q->tx_waiting = 0;
-        if (virtio_net_flush_tx(q) == -EINVAL) {
-            return;
-        }
+        virtio_net_tx_timer(q);
     } else {
+        /* re-arm timer to flush it (and more) on next tick */
         timer_mod(q->tx_timer,
-                       qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
+                  qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
         q->tx_waiting = 1;
         virtio_queue_set_notification(vq, 0);
     }
@@ -2702,6 +2707,8 @@ static void virtio_net_tx_timer(void *opaque)
     VirtIONetQueue *q = opaque;
     VirtIONet *n = q->n;
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    int ret;
+
     /* This happens when device was stopped but BH wasn't. */
     if (!vdev->vm_running) {
         /* Make sure tx waiting is set, so we'll run when restarted. */
@@ -2716,8 +2723,33 @@ static void virtio_net_tx_timer(void *opaque)
         return;
     }
 
+    ret = virtio_net_flush_tx(q);
+    if (ret == -EBUSY || ret == -EINVAL) {
+        return;
+    }
+    /*
+     * If we flush a full burst of packets, assume there are
+     * more coming and immediately rearm
+     */
+    if (ret >= n->tx_burst) {
+        q->tx_waiting = 1;
+        timer_mod(q->tx_timer,
+                  qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
+        return;
+    }
+    /*
+     * If less than a full burst, re-enable notification and flush
+     * anything that may have come in while we weren't looking.  If
+     * we find something, assume the guest is still active and rearm
+     */
     virtio_queue_set_notification(q->tx_vq, 1);
-    virtio_net_flush_tx(q);
+    ret = virtio_net_flush_tx(q);
+    if (ret > 0) {
+        virtio_queue_set_notification(q->tx_vq, 0);
+        q->tx_waiting = 1;
+        timer_mod(q->tx_timer,
+                  qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
+    }
 }
 
 static void virtio_net_tx_bh(void *opaque)
-- 
2.37.3