On Tue, Apr 25, 2017 at 1:15 PM, Eric Dumazet <eduma...@google.com> wrote:
> 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 <eduma...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
> ---
> include/linux/tcp.h | 1 +
> net/ipv4/tcp_input.c | 3 +++
> 2 files changed, 4 insertions(+)
>
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index
> cbe5b602a2d349fdeb1e878305f37b4da1e6cc86..99a22f44c32e1587a6bf4835b65c7a4314807aa8
> 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
> 5af2f04f885914491a7116c20056b3d2188d2d7d..bd18c65df4a9d9c2b66d8005f2cc4ff468140a73
> 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) {
> --
> 2.13.0.rc0.306.g87b477812d-goog
>
Nice patchset. Thanks, Eric!
