[PATCH net-next V3 6/6] tun: switch to use skb array for tx

Jason Wang
2016-06-30T03:54:50Z

We used to queue tx packets in sk_receive_queue, this is less
efficient since it requires spinlocks to synchronize between producer
and consumer.

This patch tries to address this by:

- switch from sk_receive_queue to a skb_array, and resize it when
tx_queue_len was changed.
- introduce a new proto_ops peek_len which was used for peeking the
skb length.
- implement a tun version of peek_len for vhost_net to use and convert
vhost_net to use peek_len if possible.

Pktgen test shows about 15.3% improvement on guest receiving pps for small
buffers:

Before: ~1300000pps
After : ~1500000pps

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/net.c | 16 +++++-
include/linux/net.h | 1 +
3 files changed, 146 insertions(+), 9 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4884802..3be69ea 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -71,6 +71,7 @@
#include <net/sock.h>
#include <linux/seq_file.h>
#include <linux/uio.h>
+#include <linux/skb_array.h>

#include <asm/uaccess.h>

@@ -167,6 +168,7 @@ struct tun_file {
};
struct list_head next;
struct tun_struct *detached;
+ struct skb_array tx_array;
};

struct tun_flow_entry {
@@ -515,7 +517,11 @@ static struct tun_struct *tun_enable_queue(struct tun_file *tfile)

static void tun_queue_purge(struct tun_file *tfile)
{
- skb_queue_purge(&tfile->sk.sk_receive_queue);
+ struct sk_buff *skb;
+
+ while ((skb = skb_array_consume(&tfile->tx_array)) != NULL)
+ kfree_skb(skb);
+
skb_queue_purge(&tfile->sk.sk_error_queue);
}

@@ -560,6 +566,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
tun->dev->reg_state == NETREG_REGISTERED)
unregister_netdevice(tun->dev);
}
+ if (tun)
+ skb_array_cleanup(&tfile->tx_array);
sock_put(&tfile->sk);
}
}
@@ -613,6 +621,7 @@ static void tun_detach_all(struct net_device *dev)
static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filter)
{
struct tun_file *tfile = file->private_data;
+ struct net_device *dev = tun->dev;
int err;

err = security_tun_dev_attach(tfile->socket.sk, tun->security);
@@ -642,6 +651,13 @@ static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filte
if (!err)
goto out;
}
+
+ if (!tfile->detached &&
+ skb_array_init(&tfile->tx_array, dev->tx_queue_len, GFP_KERNEL)) {
+ err = -ENOMEM;
+ goto out;
+ }
+
tfile->queue_index = tun->numqueues;
tfile->socket.sk->sk_shutdown &= ~RCV_SHUTDOWN;
rcu_assign_pointer(tfile->tun, tun);
@@ -891,8 +907,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)

nf_reset(skb);

- /* Enqueue packet */
- skb_queue_tail(&tfile->socket.sk->sk_receive_queue, skb);
+ if (skb_array_produce(&tfile->tx_array, skb))
+ goto drop;

/* Notify and wake up reader process */
if (tfile->flags & TUN_FASYNC)
@@ -1107,7 +1123,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)

poll_wait(file, sk_sleep(sk), wait);

- if (!skb_queue_empty(&sk->sk_receive_queue))
+ if (!skb_array_empty(&tfile->tx_array))
mask |= POLLIN | POLLRDNORM;

if (sock_writeable(sk) ||
@@ -1426,22 +1442,61 @@ done:
return total;
}

+static struct sk_buff *tun_ring_recv(struct tun_file *tfile, int noblock,
+ int *err)
+{
+ DECLARE_WAITQUEUE(wait, current);
+ struct sk_buff *skb = NULL;
+
+ skb = skb_array_consume(&tfile->tx_array);
+ if (skb)
+ goto out;
+ if (noblock) {
+ *err = -EAGAIN;
+ goto out;
+ }
+
+ add_wait_queue(&tfile->wq.wait, &wait);
+ current->state = TASK_INTERRUPTIBLE;
+
+ while (1) {
+ skb = skb_array_consume(&tfile->tx_array);
+ if (skb)
+ break;
+ if (signal_pending(current)) {
+ *err = -ERESTARTSYS;
+ break;
+ }
+ if (tfile->socket.sk->sk_shutdown & RCV_SHUTDOWN) {
+ *err = -EFAULT;
+ break;
+ }
+
+ schedule();
+ };
+
+ current->state = TASK_RUNNING;
+ remove_wait_queue(&tfile->wq.wait, &wait);
+
+out:
+ return skb;
+}
+
static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
struct iov_iter *to,
int noblock)
{
struct sk_buff *skb;
ssize_t ret;
- int peeked, err, off = 0;
+ int err;

tun_debug(KERN_INFO, tun, "tun_do_read\n");

if (!iov_iter_count(to))
return 0;

- /* Read frames from queue */
- skb = __skb_recv_datagram(tfile->socket.sk, noblock ? MSG_DONTWAIT : 0,
- &peeked, &off, &err);
+ /* Read frames from ring */
+ skb = tun_ring_recv(tfile, noblock, &err);
if (!skb)
return err;

@@ -1574,8 +1629,25 @@ out:
return ret;
}

+static int tun_peek_len(struct socket *sock)
+{
+ struct tun_file *tfile = container_of(sock, struct tun_file, socket);
+ struct tun_struct *tun;
+ int ret = 0;
+
+ tun = __tun_get(tfile);
+ if (!tun)
+ return 0;
+
+ ret = skb_array_peek_len(&tfile->tx_array);
+ tun_put(tun);
+
+ return ret;
+}
+
/* Ops structure to mimic raw sockets with tun */
static const struct proto_ops tun_socket_ops = {
+ .peek_len = tun_peek_len,
.sendmsg = tun_sendmsg,
.recvmsg = tun_recvmsg,
};
@@ -2397,6 +2469,53 @@ static const struct ethtool_ops tun_ethtool_ops = {
.get_ts_info = ethtool_op_get_ts_info,
};

+static int tun_queue_resize(struct tun_struct *tun)
+{
+ struct net_device *dev = tun->dev;
+ struct tun_file *tfile;
+ struct skb_array **arrays;
+ int n = tun->numqueues + tun->numdisabled;
+ int ret, i;
+
+ arrays = kmalloc(sizeof *arrays * n, GFP_KERNEL);
+ if (!arrays)
+ return -ENOMEM;
+
+ for (i = 0; i < tun->numqueues; i++) {
+ tfile = rtnl_dereference(tun->tfiles[i]);
+ arrays[i] = &tfile->tx_array;
+ }
+ list_for_each_entry(tfile, &tun->disabled, next)
+ arrays[i++] = &tfile->tx_array;
+
+ ret = skb_array_resize_multiple(arrays, n,
+ dev->tx_queue_len, GFP_KERNEL);
+
+ kfree(arrays);
+ return ret;
+}
+
+static int tun_device_event(struct notifier_block *unused,
+ unsigned long event, void *ptr)
+{
+ struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+ struct tun_struct *tun = netdev_priv(dev);
+
+ switch (event) {
+ case NETDEV_CHANGE_TX_QUEUE_LEN:
+ if (tun_queue_resize(tun))
+ return NOTIFY_BAD;
+ break;
+ default:
+ break;
+ }
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block tun_notifier_block __read_mostly = {
+ .notifier_call = tun_device_event,
+};

static int __init tun_init(void)
{
@@ -2416,6 +2535,8 @@ static int __init tun_init(void)
pr_err("Can't register misc device %d\n", TUN_MINOR);
goto err_misc;
}
+
+ register_netdevice_notifier(&tun_notifier_block);
return 0;
err_misc:
rtnl_link_unregister(&tun_link_ops);
@@ -2427,6 +2548,7 @@ static void tun_cleanup(void)
{
misc_deregister(&tun_miscdev);
rtnl_link_unregister(&tun_link_ops);
+ unregister_netdevice_notifier(&tun_notifier_block);
}

/* Get an underlying socket object from tun file. Returns error unless file is
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 1d3e45f..e032ca3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -481,10 +481,14 @@ out:

static int peek_head_len(struct sock *sk)
{
+ struct socket *sock = sk->sk_socket;
struct sk_buff *head;
int len = 0;
unsigned long flags;

+ if (sock->ops->peek_len)
+ return sock->ops->peek_len(sock);
+
spin_lock_irqsave(&sk->sk_receive_queue.lock, flags);
head = skb_peek(&sk->sk_receive_queue);
if (likely(head)) {
@@ -497,6 +501,16 @@ static int peek_head_len(struct sock *sk)
return len;
}

+static int sk_has_rx_data(struct sock *sk)
+{
+ struct socket *sock = sk->sk_socket;
+
+ if (sock->ops->peek_len)
+ return sock->ops->peek_len(sock);
+
+ return skb_queue_empty(&sk->sk_receive_queue);
+}
+
static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
{
struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
@@ -513,7 +527,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
endtime = busy_clock() + vq->busyloop_timeout;

while (vhost_can_busy_poll(&net->dev, endtime) &&
- skb_queue_empty(&sk->sk_receive_queue) &&
+ !sk_has_rx_data(sk) &&
vhost_vq_avail_empty(&net->dev, vq))
cpu_relax_lowlatency();

diff --git a/include/linux/net.h b/include/linux/net.h
index 9aa49a0..b6b3843 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -185,6 +185,7 @@ struct proto_ops {
ssize_t (*splice_read)(struct socket *sock, loff_t *ppos,
struct pipe_inode_info *pipe, size_t len, unsigned int flags);
int (*set_peek_off)(struct sock *sk, int val);
+ int (*peek_len)(struct socket *sock);
};

#define DECLARE_SOCKADDR(type, dst, src) \
--
2.7.4