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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=2815; i=leitao@debian.org; h=from:subject:message-id; bh=4lxofitPsYrHNm7bi3LfUMF9ZD1wJq6AEPk0sbeQ7X4=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBnr3hMt7hBwgflH6VNNshkd/HsByY3dQgcaq6W8 Ybx3tzUfLyJAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCZ694TAAKCRA1o5Of/Hh3 bVtXD/914iEFx6I/drSRqpQtHjhCkmfeynnlbBsXv0iOya/zzKL1lr9y7KSzQkuNaWmyhI1WfhC jfSCTXqAetgIcg3C3iBcN9jfyXleABjsQ0czTkd85Ab6JtPTyGFdP2dT5+t6E24hHVxA2Y2CAIc GqxXCxiqKEOeLlIOHuvaNNo3HhnZ6gwwwBFGFZhEBS6UF1xWslIDzEmWbmcvqiPTeksmP23MZbr 6FFrFjcalHRDqoyhghjJnRC2Wcy3ToI8xX3YIMCni3gTCQprkeqc6a6VCGoK8Zz5wsz3+oW8idn hd64jNIfHvDQpU3eRQ19DW/w7hWS9dO03l393PvJHWwDH8MJk6ETRRB+dc9FhAgifXKvriVrsxq +7mHkiyxzoExm8riELtd3EyTrFBlJwCOE2uGXD/h7svW2Fj/a1/uxt90FHyf8rMsDoxrdkP16gc 139je7c3YgM0hi2nt/Cizx0G7JOQjFVbGJ2CyvN0bYtANLv5cGHeNhuN3TT+/M90lD2/q4Kq34M 2wBuMxzxPaxm6BNBc1Gz3GLumF0bQRWeB37thxPkDoMEB3OJGOUOpBI/quWc5YazP7/cnTFC+Es N7Mrkhc3CXJKHOArGHGm460fbOEj8lxvyBDLszx9YP8vbLDQAC0fp5nGxYkn8aZf+G0VLKmBiLg AOzz1t1iax5X1kQ== 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) Given that this patch creates a rawtracepoint, you could hook into it using regular tooling, like bpftrace, using regular rawtracepoint infrastructure, such as: rawtracepoint:tcp_cwnd_reduction_tp { .... } Signed-off-by: Breno Leitao Reviewed-by: Eric Dumazet --- --- Changes in v2: - Close the parenthesis in a new line to honor the tcp.h format (Jakub). - Add the bpftrace example in the commit message (Jakub) - Link to v1: https://lore.kernel.org/r/20250207-cwnd_tracepoint-v1-1-13650f3ca96d@debian.org 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 | 6 ++++++ net/ipv4/tcp_input.c | 2 ++ 2 files changed, 8 insertions(+) --- base-commit: 7a7e0197133d18cfd9931e7d3a842d0f5730223f change-id: 20250120-cwnd_tracepoint-2e11c996a9cb Best regards, diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h index a27c4b619dffd7dcc72fffa71bf0fd5e34fe6681..1a40c41ff8c30a31b5c7002a4109de1cd8ef389e 100644 --- a/include/trace/events/tcp.h +++ b/include/trace/events/tcp.h @@ -259,6 +259,12 @@ 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 4686783b70defe0457571efd72d41ac88c528f7b..3f79718fdb1ec7a4352dc691147da527448c1f46 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2709,6 +2709,8 @@ 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 +