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Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, kernel-team@meta.com, Breno Leitao X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=2341; i=leitao@debian.org; h=from:subject:message-id; bh=tvo5NDkfWGS1QCxE9BRsTOO9ib/fhBg1vpDi7HXyydA=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBnpktBtueCo/j+Z0lpU9qnH3gCdzZ8cp6UDHd/Q j1d/m6wY1aJAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCZ6ZLQQAKCRA1o5Of/Hh3 bRUUD/0UdyGBWm96xj2/FVv0DVk7gty8wf/UptvkUkSPbo9NrXezaIKzk2idOMC6idwuWUIfdbr zxeYjTFoSwVii4pWPPCdMjvtf2szUzkZSzw++EZi0SFnIL9l3DXWcQaOrzDVMSzoLCYt9dRZHqK x/17PnNIM07geOPLFsgEbNkUAgj5cqD+U63pguPSVsHDPg2bEvsygkA63PfozdedeLB3sPeyxfx qHOQY5G0XIRuWwiB7t89yNg96M3ZY3MsWdDdiSI2AAs8I4rPJM8U7FL1BPQ4n5jR+/izL6nz5jH OVZD0BpgQpnnJZpAAhHWyCbrUp6sgvv8tlrsBCeQM2QybuQzChUX7UYLgv+XNZCB7/ZiWr5NyHh OrOH6q7TLSoaUuX+3uuAcZN91ZRjoybm2D+BYy6uh/FInn75sypNEuM+Spba7705//mgz3Gs2WZ 7SXFK9M1kYPwWlsUYefPyMdlk7NvaOX0xKQs9Vxmzm9TALU69d9C6QWI+BZAfinALMQ6U314d+v dzhKeTUoWyD4l3AUunn7Ulc1eytn2tHJFdFLRCBId9dD3LFJ+apUWZ37kAkuVWfaSGmjy/HvQc6 qJ/4bf3BTPLAsMnITBFQO8yz22gMkovromDa0/Xe0iWck92as0lS/tonLSCsoT6pa7YtYHHntAp ewDwt56xEUNBnmg== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D Add a lightweight tracepoint to monitor TCP congestion window adjustments via tcp_cwnd_reduction(). This tracepoint enables tracking of: - TCP window size fluctuations - Active socket behavior - Congestion window reduction events Meta has been using BPF programs to monitor this function for years. Adding a proper tracepoint provides a stable API for all users who need to monitor TCP congestion window behavior. Use DECLARE_TRACE instead of TRACE_EVENT to avoid creating trace event infrastructure and exporting to tracefs, keeping the implementation minimal. (Thanks Steven Rostedt) Signed-off-by: Breno Leitao Reviewed-by: Eric Dumazet --- Changes since RFC: - Change from a full tracepoint to DECLARE_TRACE() as suggested by Steven - Link to RFC: https://lore.kernel.org/r/20250120-cwnd_tracepoint-v1-1-36b0e0d643fa@debian.org --- include/trace/events/tcp.h | 5 +++++ net/ipv4/tcp_input.c | 2 ++ 2 files changed, 7 insertions(+) --- base-commit: 09717c28b76c30b1dc8c261c855ffb2406abab2e change-id: 20250120-cwnd_tracepoint-2e11c996a9cb Best regards, diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h index a27c4b619dffd7dcc72fffa71bf0fd5e34fe6681..d574e6151dc4f7430206f9ccefe0bf0d463aaa52 100644 --- a/include/trace/events/tcp.h +++ b/include/trace/events/tcp.h @@ -259,6 +259,11 @@ TRACE_EVENT(tcp_retransmit_synack, __entry->saddr_v6, __entry->daddr_v6) ); +DECLARE_TRACE(tcp_cwnd_reduction_tp, + TP_PROTO(const struct sock *sk, int newly_acked_sacked, + int newly_lost, int flag), + TP_ARGS(sk, newly_acked_sacked, newly_lost, flag)); + #include TRACE_EVENT(tcp_probe, diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index eb82e01da911048b41ca380f913ef55566be79a7..1a667e67df6beacde9871a50d44e180c2943ded0 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2710,6 +2710,8 @@ void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd)) return; + trace_tcp_cwnd_reduction_tp(sk, newly_acked_sacked, newly_lost, flag); + tp->prr_delivered += newly_acked_sacked; if (delta < 0) { u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +