[PATCH net-next 7/8] vhost_net: try batch dequing from skb array

[Jason Wang]

We used to dequeue one skb during recvmsg() from skb_array, this could
be inefficient because of the bad cache utilization and spinlock
touching for each packet. This patch tries to batch them by calling
batch dequeuing helpers explicitly on the exported skb array and pass
the skb back through msg_control for underlayer socket to finish the
userspace copying.

Tests were done by XDP1:
- small buffer:
  Before: 1.88Mpps
  After : 2.25Mpps (+19.6%)
- mergeable buffer:
  Before: 1.83Mpps
  After : 2.10Mpps (+14.7%)

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/vhost/net.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 60 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9b51989..53f09f2 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -28,6 +28,8 @@
 #include <linux/if_macvlan.h>
 #include <linux/if_tap.h>
 #include <linux/if_vlan.h>
+#include <linux/skb_array.h>
+#include <linux/skbuff.h>
 
 #include <net/sock.h>
 
@@ -85,6 +87,7 @@ struct vhost_net_ubuf_ref {
 	struct vhost_virtqueue *vq;
 };
 
+#define VHOST_RX_BATCH 64
 struct vhost_net_virtqueue {
 	struct vhost_virtqueue vq;
 	size_t vhost_hlen;
@@ -99,6 +102,10 @@ struct vhost_net_virtqueue {
 	/* Reference counting for outstanding ubufs.
 	 * Protected by vq mutex. Writers must also take device mutex. */
 	struct vhost_net_ubuf_ref *ubufs;
+	struct skb_array *rx_array;
+	void *rxq[VHOST_RX_BATCH];
+	int rt;
+	int rh;
 };
 
 struct vhost_net {
@@ -201,6 +208,8 @@ static void vhost_net_vq_reset(struct vhost_net *n)
 		n->vqs[i].ubufs = NULL;
 		n->vqs[i].vhost_hlen = 0;
 		n->vqs[i].sock_hlen = 0;
+		n->vqs[i].rt = 0;
+		n->vqs[i].rh = 0;
 	}
 
 }
@@ -503,13 +512,30 @@ static void handle_tx(struct vhost_net *net)
 	mutex_unlock(&vq->mutex);
 }
 
-static int peek_head_len(struct sock *sk)
+static int peek_head_len_batched(struct vhost_net_virtqueue *rvq)
+{
+	if (rvq->rh != rvq->rt)
+		goto out;
+
+	rvq->rh = rvq->rt = 0;
+	rvq->rt = skb_array_consume_batched_bh(rvq->rx_array, rvq->rxq,
+						VHOST_RX_BATCH);
+	if (!rvq->rt)
+		return 0;
+out:
+	return __skb_array_len_with_tag(rvq->rxq[rvq->rh]);
+}
+
+static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
 {
 	struct socket *sock = sk->sk_socket;
 	struct sk_buff *head;
 	int len = 0;
 	unsigned long flags;
 
+	if (rvq->rx_array)
+		return peek_head_len_batched(rvq);
+
 	if (sock->ops->peek_len)
 		return sock->ops->peek_len(sock);
 
@@ -535,12 +561,14 @@ static int sk_has_rx_data(struct sock *sk)
 	return skb_queue_empty(&sk->sk_receive_queue);
 }
 
-static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
+static int vhost_net_rx_peek_head_len(struct vhost_net *net,
+				      struct sock *sk)
 {
+	struct vhost_net_virtqueue *rvq = &net->vqs[VHOST_NET_VQ_RX];
 	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
 	struct vhost_virtqueue *vq = &nvq->vq;
 	unsigned long uninitialized_var(endtime);
-	int len = peek_head_len(sk);
+	int len = peek_head_len(rvq, sk);
 
 	if (!len && vq->busyloop_timeout) {
 		/* Both tx vq and rx socket were polled here */
@@ -561,7 +589,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
 			vhost_poll_queue(&vq->poll);
 		mutex_unlock(&vq->mutex);
 
-		len = peek_head_len(sk);
+		len = peek_head_len(rvq, sk);
 	}
 
 	return len;
@@ -699,6 +727,8 @@ static void handle_rx(struct vhost_net *net)
 		/* On error, stop handling until the next kick. */
 		if (unlikely(headcount < 0))
 			goto out;
+		if (nvq->rx_array)
+			msg.msg_control = nvq->rxq[nvq->rh++];
 		/* On overrun, truncate and discard */
 		if (unlikely(headcount > UIO_MAXIOV)) {
 			iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
@@ -841,6 +871,8 @@ static int vhost_net_open(struct inode *inode, struct file *f)
 		n->vqs[i].done_idx = 0;
 		n->vqs[i].vhost_hlen = 0;
 		n->vqs[i].sock_hlen = 0;
+		n->vqs[i].rt = 0;
+		n->vqs[i].rh = 0;
 	}
 	vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
 
@@ -856,11 +888,15 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
 					struct vhost_virtqueue *vq)
 {
 	struct socket *sock;
+	struct vhost_net_virtqueue *nvq =
+		container_of(vq, struct vhost_net_virtqueue, vq);
 
 	mutex_lock(&vq->mutex);
 	sock = vq->private_data;
 	vhost_net_disable_vq(n, vq);
 	vq->private_data = NULL;
+	while (nvq->rh != nvq->rt)
+		kfree_skb(nvq->rxq[nvq->rh++]);
 	mutex_unlock(&vq->mutex);
 	return sock;
 }
@@ -953,6 +989,25 @@ static struct socket *get_raw_socket(int fd)
 	return ERR_PTR(r);
 }
 
+static struct skb_array *get_tap_skb_array(int fd)
+{
+	struct skb_array *array;
+	struct file *file = fget(fd);
+
+	if (!file)
+		return NULL;
+	array = tun_get_skb_array(file);
+	if (!IS_ERR(array))
+		goto out;
+	array = tap_get_skb_array(file);
+	if (!IS_ERR(array))
+		goto out;
+	array = NULL;
+out:
+	fput(file);
+	return array;
+}
+
 static struct socket *get_tap_socket(int fd)
 {
 	struct file *file = fget(fd);
@@ -1029,6 +1084,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 
 		vhost_net_disable_vq(n, vq);
 		vq->private_data = sock;
+		nvq->rx_array = get_tap_skb_array(fd);
 		r = vhost_vq_init_access(vq);
 		if (r)
 			goto err_used;
-- 
2.7.4