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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>
This commit is contained in:
Krishna Kumar 2009-12-10 07:16:59 +00:00 committed by David S. Miller
parent afeca340c0
commit def87cf420
1 changed files with 9 additions and 8 deletions
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17
net/ipv4/tcp.c
View File

@ -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 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
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 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
/* 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