Re: [PATCH net-next 01/10] tcp: add tp->tcp_mstamp field

[Yuchung Cheng <ycheng@google.com>]

On Tue, Apr 25, 2017 at 10:15 AM, Eric Dumazet <edumazet@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 <edumazet@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 */
Eric: would this new stamp cover outgoing packet as well in the
future? in the patch series seem to cover only the incoming packets.


>         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
>