On Wed, Dec 07, 2016 at 12:12:23PM -0800, John Fastabend wrote:
> XDP requires using isolated transmit queues to avoid interference
> with normal networking stack (BQL, NETDEV_TX_BUSY, etc).
> This patch
> adds a XDP queue per cpu when a XDP program is loaded and does not
> expose the queues to the OS via the normal API call to
> netif_set_real_num_tx_queues(). This way the stack will never push
> an skb to these queues.
>
> However virtio/vhost/qemu implementation only allows for creating
> TX/RX queue pairs at this time so creating only TX queues was not
> possible. And because the associated RX queues are being created I
> went ahead and exposed these to the stack and let the backend use
> them. This creates more RX queues visible to the network stack than
> TX queues which is worth mentioning but does not cause any issues as
> far as I can tell.
>
> Signed-off-by: John Fastabend <[email protected]>
> ---
> drivers/net/virtio_net.c | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index a009299..28b1196 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -114,6 +114,9 @@ struct virtnet_info {
> /* # of queue pairs currently used by the driver */
> u16 curr_queue_pairs;
>
> + /* # of XDP queue pairs currently used by the driver */
> + u16 xdp_queue_pairs;
> +
> /* I like... big packets and I cannot lie! */
> bool big_packets;
>
> @@ -1547,7 +1550,8 @@ static int virtnet_xdp_set(struct net_device *dev,
> struct bpf_prog *prog)
> unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> struct virtnet_info *vi = netdev_priv(dev);
> struct bpf_prog *old_prog;
> - int i;
> + u16 xdp_qp = 0, curr_qp;
> + int i, err;
>
> if ((dev->features & NETIF_F_LRO) && prog) {
> netdev_warn(dev, "can't set XDP while LRO is on, disable LRO
> first\n");
> @@ -1564,12 +1568,34 @@ static int virtnet_xdp_set(struct net_device *dev,
> struct bpf_prog *prog)
> return -EINVAL;
> }
>
> + curr_qp = vi->curr_queue_pairs - vi->xdp_queue_pairs;
> + if (prog)
> + xdp_qp = nr_cpu_ids;
> +
> + /* XDP requires extra queues for XDP_TX */
> + if (curr_qp + xdp_qp > vi->max_queue_pairs) {
> + netdev_warn(dev, "request %i queues but max is %i\n",
> + curr_qp + xdp_qp, vi->max_queue_pairs);
> + return -ENOMEM;
> + }
Can't we disable XDP_TX somehow? Many people might only want RX drop,
and extra queues are not always there.
> +
> + err = virtnet_set_queues(vi, curr_qp + xdp_qp);
> + if (err) {
> + dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> + return err;
> + }
> +
> if (prog) {
> prog = bpf_prog_add(prog, vi->max_queue_pairs - 1);
> - if (IS_ERR(prog))
> + if (IS_ERR(prog)) {
> + virtnet_set_queues(vi, curr_qp);
> return PTR_ERR(prog);
> + }
> }
>
> + vi->xdp_queue_pairs = xdp_qp;
> + netif_set_real_num_rx_queues(dev, curr_qp + xdp_qp);
> +
> for (i = 0; i < vi->max_queue_pairs; i++) {
> old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
> rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
