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SubjectRe: [PATCH RFC v4 net-next 1/5] virtio_net: enable tx interrupt
On 2014/12/1 18:17, Jason Wang wrote:
> On newer hosts that support delayed tx interrupts,
> we probably don't have much to gain from orphaning
> packets early.
>
> Note: this might degrade performance for
> hosts without event idx support.
> Should be addressed by the next patch.
>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> drivers/net/virtio_net.c | 132 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 88 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..f68114e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> {
> struct skb_vnet_hdr *hdr;
> @@ -912,7 +951,9 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> sg_set_buf(sq->sg, hdr, hdr_len);
> num_sg = skb_to_sgvec(skb, sq->sg + 1, 0, skb->len) + 1;
> }
> - return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);
> +
> + return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb,
> + GFP_ATOMIC);
> }
>
> static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> @@ -924,8 +965,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
> bool kick = !skb->xmit_more;
>
> - /* Free up any pending old buffers before queueing new ones. */
> - free_old_xmit_skbs(sq);

I think there is no need to remove free_old_xmit_skbs here.
you could add free_old_xmit_skbs in tx_irq's napi func.
also could do this in start_xmit if you handle the race well.

I have done the same thing in ixgbe driver(free skb in ndo_start_xmit
and both in tx_irq's poll func), and it seems work well:)

I think there would be no so much interrupts in this way, also tx
interrupt coalesce is not needed.

> + virtqueue_disable_cb(sq->vq);
>
> /* Try to transmit */
> err = xmit_skb(sq, skb);
> @@ -941,27 +981,19 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> return NETDEV_TX_OK;
> }
>
> - /* Don't wait up for transmitted skbs to be freed. */
> - 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 (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> + if (sq->vq->num_free < 2+MAX_SKB_FRAGS)
> netif_stop_subqueue(dev, qnum);
> - if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> - /* More just got used, free them then recheck. */
> - free_old_xmit_skbs(sq);
> - if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
> - netif_start_subqueue(dev, qnum);
> - virtqueue_disable_cb(sq->vq);
> - }
> - }
> - }
>
> if (kick || netif_xmit_stopped(txq))
> virtqueue_kick(sq->vq);
>
> + if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> + virtqueue_disable_cb(sq->vq);
> + napi_schedule(&sq->napi);
> + }
> +
> return NETDEV_TX_OK;
> }
>
> @@ -1138,8 +1170,10 @@ static int virtnet_close(struct net_device *dev)
> /* Make sure refill_work doesn't re-enable napi! */
> cancel_delayed_work_sync(&vi->refill);
>
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> napi_disable(&vi->rq[i].napi);
> + napi_disable(&vi->sq[i].napi);
> + }
>
> return 0;
> }
> @@ -1452,8 +1486,10 @@ static void virtnet_free_queues(struct virtnet_info *vi)
> {
> int i;
>
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> netif_napi_del(&vi->rq[i].napi);
> + netif_napi_del(&vi->sq[i].napi);
> + }
>
> kfree(vi->rq);
> kfree(vi->sq);




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