[TCP]: Don't set SKB owner in tcp_transmit_skb().

The data itself is already charged to the SKB, doing
the skb_set_owner_w() just generates a lot of noise and
extra atomics we don't really need.

Lmbench improvements on lat_tcp are minimal:

before:
TCP latency using localhost: 23.2701 microseconds
TCP latency using localhost: 23.1994 microseconds
TCP latency using localhost: 23.2257 microseconds

after:
TCP latency using localhost: 22.8380 microseconds
TCP latency using localhost: 22.9465 microseconds
TCP latency using localhost: 22.8462 microseconds
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/inet6_connection_sock.h

@@ -38,5 +38,5 @@ extern void inet6_csk_reqsk_queue_hash_add(struct sock *sk,
 
 extern void inet6_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr);
 
-extern int inet6_csk_xmit(struct sk_buff *skb, int ipfragok);
+extern int inet6_csk_xmit(struct sk_buff *skb, struct sock *sk, int ipfragok);
 #endif /* _INET6_CONNECTION_SOCK_H */

include/net/inet_connection_sock.h

@@ -36,7 +36,8 @@ struct tcp_congestion_ops;
  * (i.e. things that depend on the address family)
  */
 struct inet_connection_sock_af_ops {
-	int	    (*queue_xmit)(struct sk_buff *skb, int ipfragok);
+	int	    (*queue_xmit)(struct sk_buff *skb, struct sock *sk,
+				  int ipfragok);
 	void	    (*send_check)(struct sock *sk, int len,
 				  struct sk_buff *skb);
 	int	    (*rebuild_header)(struct sock *sk);

include/net/ip.h

@@ -97,7 +97,7 @@ extern int		ip_mc_output(struct sk_buff *skb);
 extern int		ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *));
 extern int		ip_do_nat(struct sk_buff *skb);
 extern void		ip_send_check(struct iphdr *ip);
-extern int		ip_queue_xmit(struct sk_buff *skb, int ipfragok);
+extern int		ip_queue_xmit(struct sk_buff *skb, struct sock *sk, int ipfragok);
 extern void		ip_init(void);
 extern int		ip_append_data(struct sock *sk,
 				       int getfrag(void *from, char *to, int offset, int len,

net/dccp/output.c

@@ -125,7 +125,7 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
 		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
 
 		memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
-		err = icsk->icsk_af_ops->queue_xmit(skb, 0);
+		err = icsk->icsk_af_ops->queue_xmit(skb, sk, 0);
 		if (err <= 0)
 			return err;
 
@@ -426,7 +426,7 @@ int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
 						      code);
 		if (skb != NULL) {
 			memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
-			err = inet_csk(sk)->icsk_af_ops->queue_xmit(skb, 0);
+			err = inet_csk(sk)->icsk_af_ops->queue_xmit(skb, sk, 0);
 			if (err == NET_XMIT_CN)
 				err = 0;
 		}

net/ipv4/ip_output.c

@@ -288,9 +288,8 @@ int ip_output(struct sk_buff *skb)
 			    !(IPCB(skb)->flags & IPSKB_REROUTED));
 }
 
-int ip_queue_xmit(struct sk_buff *skb, int ipfragok)
+int ip_queue_xmit(struct sk_buff *skb, struct sock *sk, int ipfragok)
 {
-	struct sock *sk = skb->sk;
 	struct inet_sock *inet = inet_sk(sk);
 	struct ip_options *opt = inet->opt;
 	struct rtable *rt;

net/ipv4/tcp_output.c

@@ -426,7 +426,6 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 
 	th = (struct tcphdr *) skb_push(skb, tcp_header_size);
 	skb->h.th = th;
-	skb_set_owner_w(skb, sk);
 
 	/* Build TCP header and checksum it. */
 	th->source		= inet->sport;
@@ -479,7 +478,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
 		TCP_INC_STATS(TCP_MIB_OUTSEGS);
 
-	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
+	err = icsk->icsk_af_ops->queue_xmit(skb, sk, 0);
 	if (likely(err <= 0))
 		return err;
 

net/ipv6/inet6_connection_sock.c

@@ -139,9 +139,8 @@ void inet6_csk_addr2sockaddr(struct sock *sk, struct sockaddr * uaddr)
 
 EXPORT_SYMBOL_GPL(inet6_csk_addr2sockaddr);
 
-int inet6_csk_xmit(struct sk_buff *skb, int ipfragok)
+int inet6_csk_xmit(struct sk_buff *skb, struct sock *sk, int ipfragok)
 {
-	struct sock *sk = skb->sk;
 	struct inet_sock *inet = inet_sk(sk);
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct flowi fl;

net/sctp/protocol.c

@@ -808,7 +808,7 @@ static inline int sctp_v4_xmit(struct sk_buff *skb,
 			  NIPQUAD(((struct rtable *)skb->dst)->rt_dst));
 
 	SCTP_INC_STATS(SCTP_MIB_OUTSCTPPACKS);
-	return ip_queue_xmit(skb, ipfragok);
+	return ip_queue_xmit(skb, skb->sk, ipfragok);
 }
 
 static struct sctp_af sctp_ipv4_specific;