tcp: Slightly optimize tcp_sendmsg

Slightly optimize tcp_sendmsg since NETIF_F_SG is used many
times iteratively in the loop. The only other modification is
to change:
			} else if (i == MAX_SKB_FRAGS ||
				   (!i &&
				   !(sk->sk_route_caps & NETIF_F_SG))) {
	to:
			} else if (i == MAX_SKB_FRAGS || !sg) {

The reason why this change is correct: this code (other than
the MAX_SKB_FRAGS case) executes only due to the else part
of: "if (skb_tailroom(skb) > 0) {" - i.e. there was no space
in the skb to put the data inline. Hence SG is false is a
sufficient condition, and there is no way a fragment can be
added to the skb.

Changelog:
	- Added the above explanation for the change

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 8 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 8a3f05adb39b..d5d69ea8f249 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -876,12 +876,12 @@ ssize_t tcp_sendpage(struct socket *sock, struct page *page, int offset,
 #define TCP_PAGE(sk)    (sk->sk_sndmsg_page)
 #define TCP_OFF(sk)     (sk->sk_sndmsg_off)
 
-static inline int select_size(struct sock *sk)
+static inline int select_size(struct sock *sk, int sg)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         int tmp = tp->mss_cache;
 
-        if (sk->sk_route_caps & NETIF_F_SG) {
+        if (sg) {
                 if (sk_can_gso(sk))
                         tmp = 0;
                 else {
@@ -905,7 +905,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
         struct sk_buff *skb;
         int iovlen, flags;
         int mss_now, size_goal;
-        int err, copied;
+        int sg, err, copied;
         long timeo;
 
         lock_sock(sk);
@@ -933,6 +933,8 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
         if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                 goto out_err;
 
+        sg = sk->sk_route_caps & NETIF_F_SG;
+
         while (--iovlen >= 0) {
                 int seglen = iov->iov_len;
                 unsigned char __user *from = iov->iov_base;
@@ -958,8 +960,9 @@ new_segment:
                                 if (!sk_stream_memory_free(sk))
                                         goto wait_for_sndbuf;
 
-                                skb = sk_stream_alloc_skb(sk, select_size(sk),
-                                                sk->sk_allocation);
+                                skb = sk_stream_alloc_skb(sk,
+                                                          select_size(sk, sg),
+                                                          sk->sk_allocation);
                                 if (!skb)
                                         goto wait_for_memory;
 
@@ -996,9 +999,7 @@ new_segment:
                                         /* We can extend the last page
                                          * fragment. */
                                         merge = 1;
-                                } else if (i == MAX_SKB_FRAGS ||
-                                           (!i &&
-                                           !(sk->sk_route_caps & NETIF_F_SG))) {
+                                } else if (i == MAX_SKB_FRAGS || !sg) {
                                         /* Need to add new fragment and cannot
                                          * do this because interface is non-SG,
                                          * or because all the page slots are