tcp: remove false sharing in tcp_rcv_state_process()

Last known hot point during SYNFLOOD attack is the clearing
of rx_opt.saw_tstamp in tcp_rcv_state_process()

It is not needed for a listener, so we move it where it matters.

Performance while a SYNFLOOD hits a single listener socket
went from 5 Mpps to 6 Mpps on my test server (24 cores, 8 NIC RX queues)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7ea7034af83f..90e0d9256b74 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5796,8 +5796,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
         int queued = 0;
         bool acceptable;
 
-        tp->rx_opt.saw_tstamp = 0;
-
         switch (sk->sk_state) {
         case TCP_CLOSE:
                 goto discard;
@@ -5838,6 +5836,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
                 goto discard;
 
         case TCP_SYN_SENT:
+                tp->rx_opt.saw_tstamp = 0;
                 queued = tcp_rcv_synsent_state_process(sk, skb, th);
                 if (queued >= 0)
                         return queued;
@@ -5849,6 +5848,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
                 return 0;
         }
 
+        tp->rx_opt.saw_tstamp = 0;
         req = tp->fastopen_rsk;
         if (req) {
                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&