Commit def87cf4 authored by Krishna Kumar's avatar Krishna Kumar Committed by David S. Miller
Browse files

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: default avatarKrishna Kumar <krkumar2@in.ibm.com>
Acked-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent afeca340

net/ipv4/tcp.c

+9 −8
Original line number Diff line number Diff line
@@ -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;
@@ -958,7 +960,8 @@ new_segment: 
				if (!sk_stream_memory_free(sk))

					goto wait_for_sndbuf;



				skb = sk_stream_alloc_skb(sk, select_size(sk),

				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

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