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 <[email protected]> --- Changes since RFC: - Change from a full tracepoint to DECLARE_TRACE() as suggested by Steven - Link to RFC: https://lore.kernel.org/r/[email protected] --- include/trace/events/tcp.h | 5 +++++ net/ipv4/tcp_input.c | 2 ++ 2 files changed, 7 insertions(+) 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/events/net_probe_common.h> 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 + --- base-commit: 09717c28b76c30b1dc8c261c855ffb2406abab2e change-id: 20250120-cwnd_tracepoint-2e11c996a9cb Best regards, -- Breno Leitao <[email protected]>
