netdev - [PATCH net-next 00/11] tcp: receive side improvements

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Message-ID: <20250513193919.1089692-1-edumazet@google.com>
Date: Tue, 13 May 2025 19:39:08 +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 00/11] tcp: receive side improvements

We have set tcp_rmem[2] to 15 MB for about 8 years at Google,
but had some issues for high speed flows on very small RTT.

TCP rx autotuning has a tendency to overestimate the RTT,
thus tp->rcvq_space.space and sk->sk_rcvbuf.

This makes TCP receive queues much bigger than necessary,
to a point cpu caches are evicted before application can
copy the data, on cpus using DDIO.

This series aims to fix this.

- First patch adds tcp_rcvbuf_grow() tracepoint, which was very
  convenient to study the various issues fixed in this series.

- Seven patches fix receiver autotune issues.

- Two patches fix sender side issues.

- Final patch increases tcp_rmem[2] so that TCP speed over WAN
  can meet modern needs.

Tested on a 200Gbit NIC, average max throughput of a single flow:

Before:
 73593 Mbit.

After:
 122514 Mbit.

Eric Dumazet (11):
  tcp: add tcp_rcvbuf_grow() tracepoint
  tcp: fix sk_rcvbuf overshoot
  tcp: adjust rcvbuf in presence of reorders
  tcp: add receive queue awareness in tcp_rcv_space_adjust()
  tcp: remove zero TCP TS samples for autotuning
  tcp: fix initial tp->rcvq_space.space value for passive TS enabled
    flows
  tcp: always seek for minimal rtt in tcp_rcv_rtt_update()
  tcp: skip big rtt sample if receive queue is not empty
  tcp: increase tcp_limit_output_bytes default value to 4MB
  tcp: always use tcp_limit_output_bytes limitation
  tcp: increase tcp_rmem[2] to 32 MB

 Documentation/networking/ip-sysctl.rst |   4 +-
 include/linux/tcp.h                    |   2 +-
 include/trace/events/tcp.h             |  73 ++++++++++++++++
 net/ipv4/tcp.c                         |   2 +-
 net/ipv4/tcp_input.c                   | 110 ++++++++++++-------------
 net/ipv4/tcp_ipv4.c                    |   4 +-
 net/ipv4/tcp_output.c                  |   5 +-
 7 files changed, 134 insertions(+), 66 deletions(-)

-- 
2.49.0.1045.g170613ef41-goog