[PATCH net-next v2 2/4] tcp: advance the tsflags check to save cycles

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

Check the tsflags first to see if the socket timestamping is enabled.
If so, then try to fetch the last skb from either write queue or
retransmission queue.

Signed-off-by: Yushan Zhou <katrinzhou@tencent.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 net/ipv4/tcp.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 169c3fff4f6d..c603b90057f6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -484,13 +484,14 @@ void tcp_init_sock(struct sock *sk)
 
 static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
 {
-	struct sk_buff *skb = tcp_write_queue_tail(sk);
 	u32 tsflags = sockc->tsflags;
+	struct sk_buff *skb;
 
-	if (unlikely(!skb))
-		skb = skb_rb_last(&sk->tcp_rtx_queue);
+	if (!tsflags)
+		return;
 
-	if (tsflags && skb) {
+	skb = tcp_write_queue_tail(sk) ? : skb_rb_last(&sk->tcp_rtx_queue);
+	if (skb) {
 		struct skb_shared_info *shinfo = skb_shinfo(skb);
 		struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
 
-- 
2.41.3