[TCP] FRTO: Separated response from FRTO detection algorithm

FRTO spurious RTO detection algorithm (RFC4138) does not include response
to a detected spurious RTO but can use different response algorithms.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 6 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b21e232d5d33..c5be3d0465f5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2467,6 +2467,15 @@ static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
         return flag;
 }
 
+/* A very conservative spurious RTO response algorithm: reduce cwnd and
+ * continue in congestion avoidance.
+ */
+static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
+{
+        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+        tcp_moderate_cwnd(tp);
+}
+
 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
 {
         struct tcp_sock *tp = tcp_sk(sk);
@@ -2488,12 +2497,7 @@ static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
                  */
                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
         } else {
-                /* Also the second ACK after RTO advances the window.
-                 * The RTO was likely spurious. Reduce cwnd and continue
-                 * in congestion avoidance
-                 */
-                tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
-                tcp_moderate_cwnd(tp);
+                tcp_conservative_spur_to_response(tp);
         }
 
         /* F-RTO affects on two new ACKs following RTO.