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tcp: tcp_make_synack() consumes dst parameter 

tcp_make_synack() clones the dst, and callers release it.

We can avoid two atomic operations per SYNACK if tcp_make_synack()
consumes dst instead of cloning it.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-06-03 20:33:21 +00:00 committed by David S. Miller
parent 90ba9b1986
commit 4aea39c11c
3 changed files with 14 additions and 6 deletions
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1
net/ipv4/tcp_ipv4.c
View File

@ -848,7 +848,6 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
err = net_xmit_eval(err);
}
dst_release(dst);
return err;
}

18
net/ipv4/tcp_output.c
View File

@ -2442,7 +2442,16 @@ int tcp_send_synack(struct sock *sk)
return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
}
/* Prepare a SYN-ACK. */
/**
* tcp_make_synack - Prepare a SYN-ACK.
* sk: listener socket
* dst: dst entry attached to the SYNACK
* req: request_sock pointer
* rvp: request_values pointer
*
* Allocate one skb and build a SYNACK packet.
* @dst is consumed : Caller should not use it again.
*/
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct request_values *rvp)
@ -2462,13 +2471,14 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
s_data_desired = cvp->s_data_desired;
skb = alloc_skb(MAX_TCP_HEADER + 15 + s_data_desired, GFP_ATOMIC);
if (skb == NULL)
if (unlikely(!skb)) {
dst_release(dst);
return NULL;
}
/* Reserve space for headers. */
skb_reserve(skb, MAX_TCP_HEADER);
skb_dst_set(skb, dst_clone(dst));
skb_dst_set(skb, dst);
mss = dst_metric_advmss(dst);
if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)

1
net/ipv6/tcp_ipv6.c
View File

@ -522,7 +522,6 @@ static int tcp_v6_send_synack(struct sock *sk, struct request_sock *req,
done:
if (opt && opt != np->opt)
sock_kfree_s(sk, opt, opt->tot_len);
dst_release(dst);
return err;
}