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net-tun: restructure tun_do_read for better sleep/wakeup efficiency
tun_do_read always adds current thread to wait queue, even if a packet is ready to read. This is inefficient because both sleeper and waker want to acquire the wait queue spin lock when packet rate is high. We restructure the read function and use common kernel networking routines to handle receive, sleep and wakeup. With the change available packets are checked first before the reading thread is added to the wait queue. Ran performance tests with the following configuration: - my packet generator -> tap1 -> br0 -> tap0 -> my packet consumer - sender pinned to one core and receiver pinned to another core - sender send small UDP packets (64 bytes total) as fast as it can - sandy bridge cores - throughput are receiver side goodput numbers The results are baseline: 731k pkts/sec, cpu utilization at 1.50 cpus changed: 783k pkts/sec, cpu utilization at 1.53 cpus The performance difference is largely determined by packet rate and inter-cpu communication cost. For example, if the sender and receiver are pinned to different cpu sockets, the results are baseline: 558k pkts/sec, cpu utilization at 1.71 cpus changed: 690k pkts/sec, cpu utilization at 1.67 cpus Co-authored-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Xi Wang <xii@google.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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parent
f98f89a010
commit
9e641bdcfa
1 changed files with 16 additions and 38 deletions
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@ -498,12 +498,12 @@ static void tun_detach_all(struct net_device *dev)
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for (i = 0; i < n; i++) {
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tfile = rtnl_dereference(tun->tfiles[i]);
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BUG_ON(!tfile);
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wake_up_all(&tfile->wq.wait);
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tfile->socket.sk->sk_data_ready(tfile->socket.sk);
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RCU_INIT_POINTER(tfile->tun, NULL);
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--tun->numqueues;
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}
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list_for_each_entry(tfile, &tun->disabled, next) {
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wake_up_all(&tfile->wq.wait);
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tfile->socket.sk->sk_data_ready(tfile->socket.sk);
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RCU_INIT_POINTER(tfile->tun, NULL);
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}
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BUG_ON(tun->numqueues != 0);
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@ -807,8 +807,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
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/* Notify and wake up reader process */
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if (tfile->flags & TUN_FASYNC)
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kill_fasync(&tfile->fasync, SIGIO, POLL_IN);
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wake_up_interruptible_poll(&tfile->wq.wait, POLLIN |
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POLLRDNORM | POLLRDBAND);
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tfile->socket.sk->sk_data_ready(tfile->socket.sk);
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rcu_read_unlock();
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return NETDEV_TX_OK;
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@ -965,7 +964,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
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tun_debug(KERN_INFO, tun, "tun_chr_poll\n");
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poll_wait(file, &tfile->wq.wait, wait);
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poll_wait(file, sk_sleep(sk), wait);
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if (!skb_queue_empty(&sk->sk_receive_queue))
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mask |= POLLIN | POLLRDNORM;
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@ -1330,47 +1329,26 @@ static ssize_t tun_put_user(struct tun_struct *tun,
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static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
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const struct iovec *iv, ssize_t len, int noblock)
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{
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DECLARE_WAITQUEUE(wait, current);
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struct sk_buff *skb;
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ssize_t ret = 0;
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int peeked, err, off = 0;
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tun_debug(KERN_INFO, tun, "tun_do_read\n");
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if (unlikely(!noblock))
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add_wait_queue(&tfile->wq.wait, &wait);
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while (len) {
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if (unlikely(!noblock))
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current->state = TASK_INTERRUPTIBLE;
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if (!len)
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return ret;
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/* Read frames from the queue */
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if (!(skb = skb_dequeue(&tfile->socket.sk->sk_receive_queue))) {
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if (noblock) {
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ret = -EAGAIN;
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break;
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}
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if (signal_pending(current)) {
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ret = -ERESTARTSYS;
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break;
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}
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if (tun->dev->reg_state != NETREG_REGISTERED) {
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ret = -EIO;
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break;
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}
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/* Nothing to read, let's sleep */
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schedule();
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continue;
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}
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if (tun->dev->reg_state != NETREG_REGISTERED)
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return -EIO;
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/* Read frames from queue */
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skb = __skb_recv_datagram(tfile->socket.sk, noblock ? MSG_DONTWAIT : 0,
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&peeked, &off, &err);
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if (skb) {
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ret = tun_put_user(tun, tfile, skb, iv, len);
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kfree_skb(skb);
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break;
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}
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if (unlikely(!noblock)) {
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current->state = TASK_RUNNING;
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remove_wait_queue(&tfile->wq.wait, &wait);
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}
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} else
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ret = err;
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return ret;
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}
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@ -2199,8 +2177,8 @@ static int tun_chr_open(struct inode *inode, struct file * file)
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tfile->flags = 0;
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tfile->ifindex = 0;
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rcu_assign_pointer(tfile->socket.wq, &tfile->wq);
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init_waitqueue_head(&tfile->wq.wait);
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RCU_INIT_POINTER(tfile->socket.wq, &tfile->wq);
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tfile->socket.file = file;
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tfile->socket.ops = &tun_socket_ops;
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