Re: [RFC PATCH net-next 12/12] vhost_net: batch submitting XDP buffers to underlayer sockets

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 21, 2018 at 05:04:33PM +0800, Jason Wang wrote:
> This patch implements XDP batching for vhost_net with tun. This is
> done by batching XDP buffs in vhost and submit them when:
> 
> - vhost_net can not build XDP buff (mostly because of the size of packet)
> - #batched exceeds the limitation (VHOST_NET_RX_BATCH).
> - tun accept a batch of XDP buff through msg_control and process them
>   in a batch
> 
> With this tun XDP can benefit from e.g batch transmission during
> XDP_REDIRECT or XDP_TX.
> 
> Tests shows 21% improvement on TX pps (from ~3.2Mpps to ~3.9Mpps)
> while transmitting through testpmd from guest to host by
> xdp_redirect_map between tap0 and ixgbe.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>

s/underlayer/underlying/ ?

> ---
>  drivers/net/tun.c   | 36 +++++++++++++++++----------
>  drivers/vhost/net.c | 71 ++++++++++++++++++++++++++++++++++++-----------------
>  2 files changed, 71 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index b586b3f..5d16d18 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1616,7 +1616,6 @@ static u32 tun_do_xdp(struct tun_struct *tun,
>  	switch (act) {
>  	case XDP_REDIRECT:
>  		*err = xdp_do_redirect(tun->dev, xdp, xdp_prog);
> -		xdp_do_flush_map();
>  		if (*err)
>  			break;
>  		goto out;
> @@ -1624,7 +1623,6 @@ static u32 tun_do_xdp(struct tun_struct *tun,
>  		*err = tun_xdp_tx(tun->dev, xdp);
>  		if (*err)
>  			break;
> -		tun_xdp_flush(tun->dev);
>  		goto out;
>  	case XDP_PASS:
>  		goto out;
> @@ -2400,9 +2398,6 @@ static int tun_xdp_one(struct tun_struct *tun,
>  	int err = 0;
>  	bool skb_xdp = false;
>  
> -	preempt_disable();
> -	rcu_read_lock();
> -
>  	xdp_prog = rcu_dereference(tun->xdp_prog);
>  	if (xdp_prog) {
>  		if (gso->gso_type) {
> @@ -2461,15 +2456,12 @@ static int tun_xdp_one(struct tun_struct *tun,
>  		tun_flow_update(tun, rxhash, tfile);
>  
>  out:
> -	rcu_read_unlock();
> -	preempt_enable();
> -
>  	return err;
>  }
>  
>  static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
>  {
> -	int ret;
> +	int ret, i;
>  	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
>  	struct tun_struct *tun = tun_get(tfile);
>  	struct tun_msg_ctl *ctl = m->msg_control;
> @@ -2477,10 +2469,28 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
>  	if (!tun)
>  		return -EBADFD;
>  
> -	if (ctl && ctl->type == TUN_MSG_PTR) {
> -		ret = tun_xdp_one(tun, tfile, ctl->ptr);
> -		if (!ret)
> -			ret = total_len;
> +	if (ctl && ((ctl->type & 0xF) == TUN_MSG_PTR)) {
> +		int n = ctl->type >> 16;
> +
> +		preempt_disable();
> +		rcu_read_lock();
> +
> +		for (i = 0; i < n; i++) {
> +			struct xdp_buff *x = (struct xdp_buff *)ctl->ptr;
> +			struct xdp_buff *xdp = &x[i];
> +
> +			xdp_set_data_meta_invalid(xdp);
> +			xdp->rxq = &tfile->xdp_rxq;
> +			tun_xdp_one(tun, tfile, xdp);
> +		}
> +
> +		xdp_do_flush_map();
> +		tun_xdp_flush(tun->dev);
> +
> +		rcu_read_unlock();
> +		preempt_enable();
> +
> +		ret = total_len;
>  		goto out;
>  	}
>  
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 0d84de6..bec4109 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -118,6 +118,7 @@ struct vhost_net_virtqueue {
>  	struct ptr_ring *rx_ring;
>  	struct vhost_net_buf rxq;
>  	struct xdp_buff xdp[VHOST_RX_BATCH];
> +	struct vring_used_elem heads[VHOST_RX_BATCH];
>  };
>  
>  struct vhost_net {
> @@ -511,7 +512,7 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>  	void *buf;
>  	int copied;
>  
> -	if (len < nvq->sock_hlen)
> +	if (unlikely(len < nvq->sock_hlen))
>  		return -EFAULT;
>  
>  	if (SKB_DATA_ALIGN(len + pad) +
> @@ -567,11 +568,37 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>  	return 0;
>  }
>  
> +static void vhost_tx_batch(struct vhost_net *net,
> +			   struct vhost_net_virtqueue *nvq,
> +			   struct socket *sock,
> +			   struct msghdr *msghdr, int n)
> +{
> +	struct tun_msg_ctl ctl = {
> +		.type = n << 16 | TUN_MSG_PTR,
> +		.ptr = nvq->xdp,
> +	};
> +	int err;
> +
> +	if (n == 0)
> +		return;
> +
> +	msghdr->msg_control = &ctl;
> +	err = sock->ops->sendmsg(sock, msghdr, 0);
> +
> +	if (unlikely(err < 0)) {
> +		/* FIXME vq_err() */
> +		vq_err(&nvq->vq, "sendmsg err!\n");
> +		return;
> +	}
> +	vhost_add_used_and_signal_n(&net->dev, &nvq->vq, nvq->vq.heads, n);
> +}
> +
> +/* Expects to be always run from workqueue - which acts as
> + * read-size critical section for our kind of RCU. */
>  static void handle_tx_copy(struct vhost_net *net)
>  {
>  	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>  	struct vhost_virtqueue *vq = &nvq->vq;
> -	struct xdp_buff xdp;
>  	unsigned out, in;
>  	int head;
>  	struct msghdr msg = {
> @@ -586,7 +613,6 @@ static void handle_tx_copy(struct vhost_net *net)
>  	size_t hdr_size;
>  	struct socket *sock;
>  	struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
> -	struct tun_msg_ctl ctl;
>  	int sent_pkts = 0;
>  	s16 nheads = 0;
>  
> @@ -631,22 +657,24 @@ static void handle_tx_copy(struct vhost_net *net)
>  		vq->heads[nheads].id = cpu_to_vhost32(vq, head);
>  		vq->heads[nheads].len = 0;
>  
> -		err = vhost_net_build_xdp(nvq, &msg.msg_iter, &xdp);
> -		if (!err) {
> -			ctl.type = TUN_MSG_PTR;
> -			ctl.ptr = &xdp;
> -			msg.msg_control = &ctl;
> -		} else
> -			msg.msg_control = NULL;
> -
>  		total_len += len;
> -		if (total_len < VHOST_NET_WEIGHT &&
> -		    vhost_has_more_pkts(net, vq)) {
> -			msg.msg_flags |= MSG_MORE;
> -		} else {
> -			msg.msg_flags &= ~MSG_MORE;
> +		err = vhost_net_build_xdp(nvq, &msg.msg_iter,
> +					  &nvq->xdp[nheads]);
> +		if (!err) {
> +			if (++nheads == VHOST_RX_BATCH) {
> +				vhost_tx_batch(net, nvq, sock, &msg, nheads);
> +				nheads = 0;
> +			}
> +			goto done;
> +		} else if (unlikely(err != -ENOSPC)) {
> +			vq_err(vq, "Fail to build XDP buffer\n");
> +			break;
>  		}
>  
> +		vhost_tx_batch(net, nvq, sock, &msg, nheads);
> +		msg.msg_control = NULL;
> +		nheads = 0;
> +
>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(sock, &msg, len);
>  		if (unlikely(err < 0)) {
> @@ -657,11 +685,9 @@ static void handle_tx_copy(struct vhost_net *net)
>  		if (err != len)
>  			pr_debug("Truncated TX packet: "
>  				 " len %d != %zd\n", err, len);
> -		if (++nheads == VHOST_RX_BATCH) {
> -			vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> -						    nheads);
> -			nheads = 0;
> -		}
> +
> +		vhost_add_used_and_signal(&net->dev, vq, head, 0);
> +done:
>  		if (vhost_exceeds_weight(++sent_pkts, total_len)) {
>  			vhost_poll_queue(&vq->poll);
>  			break;
> @@ -669,8 +695,7 @@ static void handle_tx_copy(struct vhost_net *net)
>  	}
>  out:
>  	if (nheads)
> -		vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> -					    nheads);
> +		vhost_tx_batch(net, nvq, sock, &msg, nheads);
>  	mutex_unlock(&vq->mutex);
>  }
>  
> -- 
> 2.7.4