netdev - [PATCH net-next 0/4] tcp: scale connect() under pressure

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Message-ID: <20250302124237.3913746-1-edumazet@google.com>
Date: Sun,  2 Mar 2025 12:42:33 +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: Kuniyuki Iwashima <kuniyu@...zon.com>, Jason Xing <kerneljasonxing@...il.com>, 
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 0/4] tcp: scale connect() under pressure

Adoption of bhash2 in linux-6.1 made some operations almost twice
more expensive, because of additional locks.

This series adds RCU in __inet_hash_connect() to help the
case where many attempts need to be made before finding
an available 4-tuple.

This brings a ~200 % improvement in this experiment:

Server:
ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog

Client:
ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog -c -H server

Before series:

  utime_start=0.288582
  utime_end=1.548707
  stime_start=20.637138
  stime_end=2002.489845
  num_transactions=484453
  latency_min=0.156279245
  latency_max=20.922042756
  latency_mean=1.546521274
  latency_stddev=3.936005194
  num_samples=312537
  throughput=47426.00

perf top on the client:

 49.54%  [kernel]       [k] _raw_spin_lock
 25.87%  [kernel]       [k] _raw_spin_lock_bh
  5.97%  [kernel]       [k] queued_spin_lock_slowpath
  5.67%  [kernel]       [k] __inet_hash_connect
  3.53%  [kernel]       [k] __inet6_check_established
  3.48%  [kernel]       [k] inet6_ehashfn
  0.64%  [kernel]       [k] rcu_all_qs

After this series:

  utime_start=0.271607
  utime_end=3.847111
  stime_start=18.407684
  stime_end=1997.485557
  num_transactions=1350742
  latency_min=0.014131929
  latency_max=17.895073144
  latency_mean=0.505675853   # Nice reduction of latency metrics
  latency_stddev=2.125164772
  num_samples=307884
  throughput=139866.80       # 194 % increase

perf top on client:

 56.86%  [kernel]       [k] __inet6_check_established
 17.96%  [kernel]       [k] __inet_hash_connect
 13.88%  [kernel]       [k] inet6_ehashfn
  2.52%  [kernel]       [k] rcu_all_qs
  2.01%  [kernel]       [k] __cond_resched
  0.41%  [kernel]       [k] _raw_spin_lock

Eric Dumazet (4):
  tcp: use RCU in __inet{6}_check_established()
  tcp: optimize inet_use_bhash2_on_bind()
  tcp: add RCU management to inet_bind_bucket
  tcp: use RCU lookup in __inet_hash_connect()

 include/net/inet_hashtables.h   |  7 ++--
 net/ipv4/inet_connection_sock.c |  8 ++--
 net/ipv4/inet_hashtables.c      | 65 ++++++++++++++++++++++++---------
 net/ipv4/inet_timewait_sock.c   |  2 +-
 net/ipv6/inet6_hashtables.c     | 23 ++++++++++--
 5 files changed, 75 insertions(+), 30 deletions(-)

-- 
2.48.1.711.g2feabab25a-goog