netdev - [PATCH net-next 09/11] tcp: increase tcp_limit_output

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Message-ID: <20250513193919.1089692-10-edumazet@google.com>
Date: Tue, 13 May 2025 19:39:17 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Rick Jones <jonesrick@...gle.com>, Wei Wang <weiwan@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 09/11] tcp: increase tcp_limit_output_bytes default
 value to 4MB

Last change happened in 2018 with commit c73e5807e4f6
("tcp: tsq: no longer use limit_output_bytes for paced flows")

Modern NIC speeds got a 4x increase since then.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 Documentation/networking/ip-sysctl.rst | 2 +-
 net/ipv4/tcp_ipv4.c                    | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index b43222ee57cf9e54e38cb78f752f050c2f43a5cf..91b7d0a1c7fd884ee964d5be0d4dbd10ce040f76 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1099,7 +1099,7 @@ tcp_limit_output_bytes - INTEGER
 	limits the number of bytes on qdisc or device to reduce artificial
 	RTT/cwnd and reduce bufferbloat.
 
-	Default: 1048576 (16 * 65536)
+	Default: 4194304 (4 MB)
 
 tcp_challenge_ack_limit - INTEGER
 	Limits number of Challenge ACK sent per second, as recommended
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d5b5c32115d2ef84b0c91d43f584e571f342d9fb..6a14f9e6fef645511be5738e0ead22e168fb20b2 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -3495,8 +3495,8 @@ static int __net_init tcp_sk_init(struct net *net)
 	 * which are too large can cause TCP streams to be bursty.
 	 */
 	net->ipv4.sysctl_tcp_tso_win_divisor = 3;
-	/* Default TSQ limit of 16 TSO segments */
-	net->ipv4.sysctl_tcp_limit_output_bytes = 16 * 65536;
+	/* Default TSQ limit of 4 MB */
+	net->ipv4.sysctl_tcp_limit_output_bytes = 4 << 20;
 
 	/* rfc5961 challenge ack rate limiting, per net-ns, disabled by default. */
 	net->ipv4.sysctl_tcp_challenge_ack_limit = INT_MAX;
-- 
2.49.0.1045.g170613ef41-goog