net: tcp: Log the steps in the collision avoidance

To allow insighed into the correct functioning of the collision avoidance,
log the internal values and function calls.

Signed-off-by: Sjors Hettinga <s.a.hettinga@gmail.com>

subsys/net/ip/tcp.c

@@ -397,25 +397,36 @@ static void tcp_derive_rto(struct tcp *conn)
 }
 
 #ifdef CONFIG_NET_TCP_CONGESTION_AVOIDANCE
+
+static void tcp_new_reno_log(struct tcp *conn, char *step)
+{
+	NET_DBG("conn: %p, ca %s, win=%d, ssthres=%d, state=%s",
+		conn, step, conn->ca.congestion_win, conn->ca.ssthresh,
+		TCP_NEW_RENO_STATE_STR(conn->ca.state));
+}
+
 static void tcp_new_reno_init(struct tcp *conn)
 {
 	conn->ca.congestion_win = conn_mss(conn) * TCP_CONGESTION_INITIAL_WIN;
 	conn->ca.ssthresh = conn_mss(conn) * TCP_CONGESTION_INITIAL_SSTHRESH;
 	conn->ca.state = TCP_NEW_RENO_RAMPUP;
+	tcp_new_reno_log(conn, "init");
 }
 
 static void tcp_new_reno_fast_retransmit(struct tcp *conn)
 {
 	conn->ca.congestion_win = MAX(conn_mss(conn), conn->ca.congestion_win / 2);
 	conn->ca.ssthresh = MAX(conn_mss(conn) * 2, conn->ca.congestion_win);
 	conn->ca.state = TCP_NEW_RENO_LINEAR;
+	tcp_new_reno_log(conn, "fast_retransmit");
 }
 
 static void tcp_new_reno_timeout(struct tcp *conn)
 {
 	conn->ca.ssthresh = conn->ca.congestion_win / 2;
 	conn->ca.congestion_win = conn_mss(conn) * TCP_CONGESTION_INITIAL_WIN;
 	conn->ca.state = TCP_NEW_RENO_RAMPUP;
+	tcp_new_reno_log(conn, "timeout");
 }
 
 static void tcp_new_reno_pkts_acked(struct tcp *conn)
@@ -434,6 +445,7 @@ static void tcp_new_reno_pkts_acked(struct tcp *conn)
 	if (conn->ca.congestion_win > conn->ca.ssthresh) {
 		conn->ca.state = TCP_NEW_RENO_LINEAR;
 	}
+	tcp_new_reno_log(conn, "pkts_acked");
 }
 #endif
 

subsys/net/ip/tcp_private.h

@@ -230,6 +230,8 @@ enum tcp_new_reno_state {
 	TCP_NEW_RENO_LINEAR
 };
 
+#define TCP_NEW_RENO_STATE_STR(x) (((x) == TCP_NEW_RENO_RAMPUP) ? "ramp-up" : "linear")
+
 struct tcp_collision_avoidance_reno {
 	uint16_t congestion_win;
 	uint16_t ssthresh;