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Date: Wed, 22 Mar 2017 16:16:10 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 7/8] vhost_net: try batch dequing from skb array
On Tue, Mar 21, 2017 at 12:04:46PM +0800, Jason Wang wrote:
> 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@...hat.com>
> ---
> 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)
Pls rename to say what it actually does: fetch skbs
> +{
> + 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);
A comment explaining why is is -bh would be helpful.
> + 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
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