On Fri, Sep 13, 2019 at 4:23 PM Thomas Higdon <t...@fb.com> wrote:
>
> Neal Cardwell mentioned that snd_wnd would be useful for diagnosing TCP
> performance problems --
> > (1) Usually when we're diagnosing TCP performance problems, we do so
> > from the sender, since the sender makes most of the
> > performance-critical decisions (cwnd, pacing, TSO size, TSQ, etc).
> > From the sender-side the thing that would be most useful is to see
> > tp->snd_wnd, the receive window that the receiver has advertised to
> > the sender.
>
> This serves the purpose of adding an additional __u32 to avoid the
> would-be hole caused by the addition of the tcpi_rcvi_ooopack field.
>
> Signed-off-by: Thomas Higdon <t...@fb.com>
> ---
Acked-by: Yuchung Cheng <ych...@google.com>
> changes since v4:
> - clarify comment
> include/uapi/linux/tcp.h | 4 ++++
> net/ipv4/tcp.c | 1 +
> 2 files changed, 5 insertions(+)
>
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index 20237987ccc8..81e697978e8b 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -272,6 +272,10 @@ struct tcp_info {
> __u32 tcpi_reord_seen; /* reordering events seen */
>
> __u32 tcpi_rcv_ooopack; /* Out-of-order packets received */
> +
> + __u32 tcpi_snd_wnd; /* peer's advertised receive window after
> + * scaling (bytes)
> + */
> };
>
> /* netlink attributes types for SCM_TIMESTAMPING_OPT_STATS */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 4cf58208270e..79c325a07ba5 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3297,6 +3297,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info
> *info)
> info->tcpi_dsack_dups = tp->dsack_dups;
> info->tcpi_reord_seen = tp->reord_seen;
> info->tcpi_rcv_ooopack = tp->rcv_ooopack;
> + info->tcpi_snd_wnd = tp->snd_wnd;
> unlock_sock_fast(sk, slow);
> }
> EXPORT_SYMBOL_GPL(tcp_get_info);
> --
> 2.17.1
>
