[TCP] Westwood: reset RTT min after FRTO

RTT_min is updated each time a timeout event occurs
in order to cope with hard handovers in wireless scenarios such as UMTS.

Signed-off-by: Luca De Cicco <ldecicco@gmail.com>
Signed-off-by: Stephen Hemminger <shemminger@dxpl.pdx.osdl.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 2 deletions

diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index edf2ee19a8ba..4247da1384bf 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -40,6 +40,7 @@ struct westwood {
         u32    rtt;
         u32    rtt_min;          /* minimum observed RTT */
         u8     first_ack;        /* flag which infers that this is the first ack */
+        u8     reset_rtt_min;    /* Reset RTT min to next RTT sample*/
 };
 
 
@@ -67,6 +68,7 @@ static void tcp_westwood_init(struct sock *sk)
         w->bw_est = 0;
         w->accounted = 0;
         w->cumul_ack = 0;
+        w->reset_rtt_min = 1;
         w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
         w->rtt_win_sx = tcp_time_stamp;
         w->snd_una = tcp_sk(sk)->snd_una;
@@ -142,6 +144,16 @@ static void westwood_update_window(struct sock *sk)
         }
 }
 
+static inline void update_rtt_min(struct westwood *w)
+{
+        if (w->reset_rtt_min) {
+                w->rtt_min = w->rtt;
+                w->reset_rtt_min = 0;   
+        } else
+                w->rtt_min = min(w->rtt, w->rtt_min);
+}
+
+
 /*
  * @westwood_fast_bw
  * It is called when we are in fast path. In particular it is called when
@@ -157,7 +169,7 @@ static inline void westwood_fast_bw(struct sock *sk)
 
         w->bk += tp->snd_una - w->snd_una;
         w->snd_una = tp->snd_una;
-        w->rtt_min = min(w->rtt, w->rtt_min);
+        update_rtt_min(w);
 }
 
 /*
@@ -226,12 +238,14 @@ static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
 
         case CA_EVENT_FRTO:
                 tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+                /* Update RTT_min when next ack arrives */
+                w->reset_rtt_min = 1;
                 break;
 
         case CA_EVENT_SLOW_ACK:
                 westwood_update_window(sk);
                 w->bk += westwood_acked_count(sk);
-                w->rtt_min = min(w->rtt, w->rtt_min);
+                update_rtt_min(w);
                 break;
 
         default: