1 files changed, 57 insertions, 14 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 82de7860368..4475b3bb494 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -285,6 +285,8 @@ int sysctl_tcp_fin_timeout __read_mostly = TCP_FIN_TIMEOUT;
 
 int sysctl_tcp_min_tso_segs __read_mostly = 2;
 
+int sysctl_tcp_autocorking __read_mostly = 1;
+
 struct percpu_counter tcp_orphan_count;
 EXPORT_SYMBOL_GPL(tcp_orphan_count);
 
@@ -379,7 +381,7 @@ void tcp_init_sock(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	skb_queue_head_init(&tp->out_of_order_queue);
+	__skb_queue_head_init(&tp->out_of_order_queue);
 	tcp_init_xmit_timers(sk);
 	tcp_prequeue_init(tp);
 	INIT_LIST_HEAD(&tp->tsq_node);
@@ -619,19 +621,58 @@ static inline void tcp_mark_urg(struct tcp_sock *tp, int flags)
 		tp->snd_up = tp->write_seq;
 }
 
-static inline void tcp_push(struct sock *sk, int flags, int mss_now,
-			    int nonagle)
+/* If a not yet filled skb is pushed, do not send it if
+ * we have data packets in Qdisc or NIC queues :
+ * Because TX completion will happen shortly, it gives a chance
+ * to coalesce future sendmsg() payload into this skb, without
+ * need for a timer, and with no latency trade off.
+ * As packets containing data payload have a bigger truesize
+ * than pure acks (dataless) packets, the last checks prevent
+ * autocorking if we only have an ACK in Qdisc/NIC queues,
+ * or if TX completion was delayed after we processed ACK packet.
+ */
+static bool tcp_should_autocork(struct sock *sk, struct sk_buff *skb,
+				int size_goal)
 {
-	if (tcp_send_head(sk)) {
-		struct tcp_sock *tp = tcp_sk(sk);
+	return skb->len < size_goal &&
+	       sysctl_tcp_autocorking &&
+	       skb != tcp_write_queue_head(sk) &&
+	       atomic_read(&sk->sk_wmem_alloc) > skb->truesize;
+}
+
+static void tcp_push(struct sock *sk, int flags, int mss_now,
+		     int nonagle, int size_goal)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct sk_buff *skb;
 
-		if (!(flags & MSG_MORE) || forced_push(tp))
-			tcp_mark_push(tp, tcp_write_queue_tail(sk));
+	if (!tcp_send_head(sk))
+		return;
+
+	skb = tcp_write_queue_tail(sk);
+	if (!(flags & MSG_MORE) || forced_push(tp))
+		tcp_mark_push(tp, skb);
+
+	tcp_mark_urg(tp, flags);
+
+	if (tcp_should_autocork(sk, skb, size_goal)) {
 
-		tcp_mark_urg(tp, flags);
-		__tcp_push_pending_frames(sk, mss_now,
-					  (flags & MSG_MORE) ? TCP_NAGLE_CORK : nonagle);
+		/* avoid atomic op if TSQ_THROTTLED bit is already set */
+		if (!test_bit(TSQ_THROTTLED, &tp->tsq_flags)) {
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPAUTOCORKING);
+			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
+		}
+		/* It is possible TX completion already happened
+		 * before we set TSQ_THROTTLED.
+		 */
+		if (atomic_read(&sk->sk_wmem_alloc) > skb->truesize)
+			return;
 	}
+
+	if (flags & MSG_MORE)
+		nonagle = TCP_NAGLE_CORK;
+
+	__tcp_push_pending_frames(sk, mss_now, nonagle);
 }
 
 static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
@@ -934,7 +975,8 @@ new_segment:
 wait_for_sndbuf:
 		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 wait_for_memory:
-		tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);
+		tcp_push(sk, flags & ~MSG_MORE, mss_now,
+			 TCP_NAGLE_PUSH, size_goal);
 
 		if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
 			goto do_error;
@@ -944,7 +986,7 @@ wait_for_memory:
 
 out:
 	if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
-		tcp_push(sk, flags, mss_now, tp->nonagle);
+		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
 	return copied;
 
 do_error:
@@ -1225,7 +1267,8 @@ wait_for_sndbuf:
 			set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 wait_for_memory:
 			if (copied)
-				tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);
+				tcp_push(sk, flags & ~MSG_MORE, mss_now,
+					 TCP_NAGLE_PUSH, size_goal);
 
 			if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
 				goto do_error;
@@ -1236,7 +1279,7 @@ wait_for_memory:
 
 out:
 	if (copied)
-		tcp_push(sk, flags, mss_now, tp->nonagle);
+		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
 	release_sock(sk);
 	return copied + copied_syn;