virtio: wean net driver off NETDEV_TX_BUSY
Herbert tells me that returning NETDEV_TX_BUSY from hard_start_xmit is
seen as a poor thing to do; we should cache the packet and stop the queue.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fc7eeaa..e441164 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -41,6 +41,9 @@
struct net_device *dev;
struct napi_struct napi;
+ /* The skb we couldn't send because buffers were full. */
+ struct sk_buff *last_xmit_skb;
+
/* Number of input buffers, and max we've ever had. */
unsigned int num, max;
@@ -227,17 +230,16 @@
}
}
-static int start_xmit(struct sk_buff *skb, struct net_device *dev)
+static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
{
- struct virtnet_info *vi = netdev_priv(dev);
- int num, err;
+ int num;
struct scatterlist sg[2+MAX_SKB_FRAGS];
struct virtio_net_hdr *hdr;
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
sg_init_table(sg, 2+MAX_SKB_FRAGS);
- pr_debug("%s: xmit %p " MAC_FMT "\n", dev->name, skb,
+ pr_debug("%s: xmit %p " MAC_FMT "\n", vi->dev->name, skb,
dest[0], dest[1], dest[2],
dest[3], dest[4], dest[5]);
@@ -272,30 +274,51 @@
vnet_hdr_to_sg(sg, skb);
num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
- __skb_queue_head(&vi->send, skb);
+
+ return vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
+}
+
+static int start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+ struct virtnet_info *vi = netdev_priv(dev);
again:
/* Free up any pending old buffers before queueing new ones. */
free_old_xmit_skbs(vi);
- err = vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
- if (err) {
- pr_debug("%s: virtio not prepared to send\n", dev->name);
- netif_stop_queue(dev);
- /* Activate callback for using skbs: if this returns false it
- * means some were used in the meantime. */
- if (unlikely(!vi->svq->vq_ops->enable_cb(vi->svq))) {
- vi->svq->vq_ops->disable_cb(vi->svq);
- netif_start_queue(dev);
- goto again;
+ /* If we has a buffer left over from last time, send it now. */
+ if (vi->last_xmit_skb) {
+ if (xmit_skb(vi, vi->last_xmit_skb) != 0) {
+ /* Drop this skb: we only queue one. */
+ vi->dev->stats.tx_dropped++;
+ kfree_skb(skb);
+ goto stop_queue;
}
- __skb_unlink(skb, &vi->send);
-
- return NETDEV_TX_BUSY;
+ vi->last_xmit_skb = NULL;
}
- vi->svq->vq_ops->kick(vi->svq);
- return 0;
+ /* Put new one in send queue and do transmit */
+ __skb_queue_head(&vi->send, skb);
+ if (xmit_skb(vi, skb) != 0) {
+ vi->last_xmit_skb = skb;
+ goto stop_queue;
+ }
+done:
+ vi->svq->vq_ops->kick(vi->svq);
+ return NETDEV_TX_OK;
+
+stop_queue:
+ pr_debug("%s: virtio not prepared to send\n", dev->name);
+ netif_stop_queue(dev);
+
+ /* Activate callback for using skbs: if this returns false it
+ * means some were used in the meantime. */
+ if (unlikely(!vi->svq->vq_ops->enable_cb(vi->svq))) {
+ vi->svq->vq_ops->disable_cb(vi->svq);
+ netif_start_queue(dev);
+ goto again;
+ }
+ goto done;
}
#ifdef CONFIG_NET_POLL_CONTROLLER