On Wed, Mar 16, 2011 at 05:12:55PM -0700, Shirley Ma wrote:
> Signed-off-by: Shirley Ma <xma@xxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 39 ++++++++++++++++++++-------------------
> 1 files changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 82dba5a..c603daa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -23,6 +23,7 @@
> #include <linux/module.h>
> #include <linux/virtio.h>
> #include <linux/virtio_net.h>
> +#include <linux/virtio_ring.h>
> #include <linux/scatterlist.h>
> #include <linux/if_vlan.h>
> #include <linux/slab.h>
> @@ -509,19 +510,18 @@ again:
> return received;
> }
>
> -static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
> +static void free_old_xmit_skbs(struct virtnet_info *vi)
> {
> struct sk_buff *skb;
> - unsigned int len, tot_sgs = 0;
> + unsigned int len;
>
> while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
> pr_debug("Sent skb %p\n", skb);
> vi->dev->stats.tx_bytes += skb->len;
> vi->dev->stats.tx_packets++;
> - tot_sgs += skb_vnet_hdr(skb)->num_sg;
> dev_kfree_skb_any(skb);
> }
> - return tot_sgs;
> + return;
> }
>
> static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
> @@ -574,11 +574,26 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
> static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> struct virtnet_info *vi = netdev_priv(dev);
> + bool drop;
> + bool indirect = virtio_has_feature(vi->vdev,
> + VIRTIO_RING_F_INDIRECT_DESC);
> int capacity;
>
> /* Free up any pending old buffers before queueing new ones. */
> free_old_xmit_skbs(vi);
> -
> + capacity = virtqueue_get_capacity(vi->svq);
> +
> + /* Drop packet instead of stop queue for better performance */
> + drop = (capacity == 0 && indirect) ||
> + ((capacity < MAX_SKB_FRAGS + 2) && !indirect);
> + if (unlikely(drop)) {
> + dev->stats.tx_fifo_errors++;
> + dev_warn(&dev->dev, "Unexpected TX queue failure: %d\n",
> + capacity);
> + dev->stats.tx_dropped++;
> + kfree_skb(skb);
> + return NETDEV_TX_OK;
> + }
> /* Try to transmit */
> capacity = xmit_skb(vi, skb);
So, this just tries to make sure there's enough space for
max packet in the ring, if not - drop and return OK.
Why bother checking beforehand though?
If that's what we want to do, we can just call add_buf and see
if it fails?
> @@ -605,20 +620,6 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> skb_orphan(skb);
> nf_reset(skb);
>
> - /* Apparently nice girls don't return TX_BUSY; stop the queue
> - * before it gets out of hand. Naturally, this wastes entries. */
> - if (capacity < 2+MAX_SKB_FRAGS) {
> - netif_stop_queue(dev);
> - if (unlikely(!virtqueue_enable_cb(vi->svq))) {
> - /* More just got used, free them then recheck. */
> - capacity += free_old_xmit_skbs(vi);
> - if (capacity >= 2+MAX_SKB_FRAGS) {
> - netif_start_queue(dev);
> - virtqueue_disable_cb(vi->svq);
> - }
> - }
> - }
> -
> return NETDEV_TX_OK;
> }
>
>
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