[PATCH net-next] tcp: tcp_make_synack() consumes dst parameter
From: Eric Dumazet <hidden>
Date: 2012-06-04 06:33:25
From: Eric Dumazet <edumazet@google.com> 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> --- To be applied after "tcp: tcp_make_synack() can use alloc_skb()" net/ipv4/tcp_ipv4.c | 1 - net/ipv4/tcp_output.c | 18 ++++++++++++++---- net/ipv6/tcp_ipv6.c | 1 - 3 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index c8d28c4..3d9c1a4 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c@@ -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; }
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f0b0e44..c465d3e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c@@ -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)
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 3a9aec2..8075825 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c@@ -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; }