netdev - [PATCH v5 2/2] tcp: Add snd_wnd to TCP

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Date:   Fri, 13 Sep 2019 23:23:35 +0000
From:   Thomas Higdon <tph@...com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Jonathan Lemon <jonathan.lemon@...il.com>, Dave Jones <dsj@...com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        "Dave Taht" <dave.taht@...il.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        "Soheil Hassas Yeganeh" <soheil@...gle.com>
Subject: [PATCH v5 2/2] tcp: Add snd_wnd to TCP_INFO

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 <tph@...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