net: tcp: Add trace events for TCP congestion window tracing

This adds an event to trace TCP stat variables with
slightly intrusive trace-event. This uses ftrace/perf
event log buffer to trace those state, no needs to
prepare own ring-buffer, nor custom user apps.

User can use ftrace to trace this event as below;

  # cd /sys/kernel/debug/tracing
  # echo 1 > events/tcp/tcp_probe/enable
  (run workloads)
  # cat trace

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4d55c4b338ee..ff71b18d9682 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5299,6 +5299,9 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
         unsigned int len = skb->len;
         struct tcp_sock *tp = tcp_sk(sk);
 
+        /* TCP congestion window tracking */
+        trace_tcp_probe(sk, skb);
+
         tcp_mstamp_refresh(tp);
         if (unlikely(!sk->sk_rx_dst))
                 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);