From: Eric Dumazet <edumazet@google.com>
Date: Tue, 13 May 2025 19:39:16 +0000 (+0000)
Subject: tcp: skip big rtt sample if receive queue is not empty
X-Git-Tag: v6.16-rc1~132^2~97^2~3
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=a00f135cd986f7d23f59723f4f9d531f38867d9d;p=linux-block.git

tcp: skip big rtt sample if receive queue is not empty

tcp_rcv_rtt_update() role is to keep an estimation
of RTT (tp->rcv_rtt_est.rtt_us) for receivers.

If an application is too slow to drain the TCP receive
queue, it is better to leave the RTT estimation small,
so that tcp_rcv_space_adjust() does not inflate
tp->rcvq_space.space and sk->sk_rcvbuf.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250513193919.1089692-9-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4723d6964925..8ec92dec321a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -682,6 +682,9 @@ static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 		 */
 		if (win_dep)
 			return;
+		/* Do not use this sample if receive queue is not empty. */
+		if (tp->rcv_nxt != tp->copied_seq)
+			return;
 		new_sample = old_sample - (old_sample >> 3) + sample;
 	}