From c4221a8cc3a719a3926a330c4fe15e2b15abe662 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 13 May 2025 19:39:18 +0000 Subject: [PATCH] tcp: always use tcp_limit_output_bytes limitation This partially reverts commit c73e5807e4f6 ("tcp: tsq: no longer use limit_output_bytes for paced flows") Overriding the tcp_limit_output_bytes sysctl value for FQ enabled flows has the following problem: It allows TCP to queue around 2 ms worth of data per flow, defeating tcp_rcv_rtt_update() accuracy on the receiver, forcing it to increase sk->sk_rcvbuf even if the real RTT is around 100 us. After this change, we keep enough packets in flight to fill the pipe, and let receive queues small enough to get good cache behavior (cpu caches and/or NIC driver page pools). Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20250513193919.1089692-11-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_output.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 13295a59d22e..3ac8d2d17e1f 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2619,9 +2619,8 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb, limit = max_t(unsigned long, 2 * skb->truesize, READ_ONCE(sk->sk_pacing_rate) >> READ_ONCE(sk->sk_pacing_shift)); - if (sk->sk_pacing_status == SK_PACING_NONE) - limit = min_t(unsigned long, limit, - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes)); + limit = min_t(unsigned long, limit, + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes)); limit <<= factor; if (static_branch_unlikely(&tcp_tx_delay_enabled) && -- 2.50.1