tcp: add tp->tcp_mstamp field

We want to use precise timestamps in TCP stack, but we do not
want to call possibly expensive kernel time services too often.

tp->tcp_mstamp is guaranteed to be updated once per incoming packet.

We will use it in the following patches, removing specific
skb_mstamp_get() calls, and removing ack_time from
struct tcp_sacktag_state.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index cbe5b602a2d3..99a22f44c32e 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -240,6 +240,7 @@ struct tcp_sock {
         u32     tlp_high_seq;   /* snd_nxt at the time of TLP retransmit. */
 
 /* RTT measurement */
+        struct skb_mstamp tcp_mstamp; /* most recent packet received/sent */
         u32     srtt_us;        /* smoothed round trip time << 3 in usecs */
         u32     mdev_us;        /* medium deviation                     */
         u32     mdev_max_us;    /* maximal mdev for the last rtt period */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5af2f04f8859..bd18c65df4a9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5362,6 +5362,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
+        skb_mstamp_get(&tp->tcp_mstamp);
         if (unlikely(!sk->sk_rx_dst))
                 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
         /*
@@ -5922,6 +5923,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 
         case TCP_SYN_SENT:
                 tp->rx_opt.saw_tstamp = 0;
+                skb_mstamp_get(&tp->tcp_mstamp);
                 queued = tcp_rcv_synsent_state_process(sk, skb, th);
                 if (queued >= 0)
                         return queued;
@@ -5933,6 +5935,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
                 return 0;
         }
 
+        skb_mstamp_get(&tp->tcp_mstamp);
         tp->rx_opt.saw_tstamp = 0;
         req = tp->fastopen_rsk;
         if (req) {