tcp: add low latency socket poll support.

Adds low latency socket poll support for TCP.
In tcp_v[46]_rcv() add a call to sk_mark_ll() to copy the napi_id
from the skb to the sk.
In tcp_recvmsg(), when there is no data in the socket we busy-poll.
This is a good example of how to add busy-poll support to more protocols.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Tested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -279,6 +279,7 @@
 
 #include <asm/uaccess.h>
 #include <asm/ioctls.h>
+#include <net/ll_poll.h>
 
 int sysctl_tcp_fin_timeout __read_mostly = TCP_FIN_TIMEOUT;
 
@@ -1553,6 +1554,10 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	struct sk_buff *skb;
 	u32 urg_hole = 0;
 
+	if (sk_valid_ll(sk) && skb_queue_empty(&sk->sk_receive_queue)
+	    && (sk->sk_state == TCP_ESTABLISHED))
+		sk_poll_ll(sk, nonblock);
+
 	lock_sock(sk);
 
 	err = -ENOTCONN;

net/ipv4/tcp_ipv4.c

@@ -75,6 +75,7 @@
 #include <net/netdma.h>
 #include <net/secure_seq.h>
 #include <net/tcp_memcontrol.h>
+#include <net/ll_poll.h>
 
 #include <linux/inet.h>
 #include <linux/ipv6.h>
@@ -1993,6 +1994,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (sk_filter(sk, skb))
 		goto discard_and_relse;
 
+	sk_mark_ll(sk, skb);
 	skb->dev = NULL;
 
 	bh_lock_sock_nested(sk);

net/ipv6/tcp_ipv6.c

@@ -63,6 +63,7 @@
 #include <net/inet_common.h>
 #include <net/secure_seq.h>
 #include <net/tcp_memcontrol.h>
+#include <net/ll_poll.h>
 
 #include <asm/uaccess.h>
 
@@ -1498,6 +1499,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
 	if (sk_filter(sk, skb))
 		goto discard_and_relse;
 
+	sk_mark_ll(sk, skb);
 	skb->dev = NULL;
 
 	bh_lock_sock_nested(sk);