netdev - [PATCH net] tcp: fix rate_app

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Message-Id: <20230119190028.1098755-1-morleyd.kernel@gmail.com>
Date:   Thu, 19 Jan 2023 19:00:28 +0000
From:   David Morley <morleyd.kernel@...il.com>
To:     David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, David Morley <morleyd@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net] tcp: fix rate_app_limited to default to 1

From: David Morley <morleyd@...gle.com>

The initial default value of 0 for tp->rate_app_limited was incorrect,
since a flow is indeed application-limited until it first sends
data. Fixing the default to be 1 is generally correct but also
specifically will help user-space applications avoid using the initial
tcpi_delivery_rate value of 0 that persists until the connection has
some non-zero bandwidth sample.

Fixes: eb8329e0a04d ("tcp: export data delivery rate")
Suggested-by: Yuchung Cheng <ycheng@...gle.com>
Signed-off-by: David Morley <morleyd@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Tested-by: David Morley <morleyd@...gle.com>
---
 net/ipv4/tcp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c567d5e8053e..33f559f491c8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -435,6 +435,7 @@ void tcp_init_sock(struct sock *sk)
 
 	/* There's a bubble in the pipe until at least the first ACK. */
 	tp->app_limited = ~0U;
+	tp->rate_app_limited = 1;
 
 	/* See draft-stevens-tcpca-spec-01 for discussion of the
 	 * initialization of these values.
@@ -3178,6 +3179,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->plb_rehash = 0;
 	/* There's a bubble in the pipe until at least the first ACK. */
 	tp->app_limited = ~0U;
+	tp->rate_app_limited = 1;
 	tp->rack.mstamp = 0;
 	tp->rack.advanced = 0;
 	tp->rack.reo_wnd_steps = 1;
-- 
2.39.0.246.g2a6d74b583-goog