tcp: tcp_vegas ssthresh bugfix

This patch fixes ssthresh accounting issues in tcp_vegas when cwnd decreases

Signed-off-by: Doug Leith <doug.leith@nuim.ie>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index a453aac91bd3..c6743eec9b7d 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -158,6 +158,11 @@ void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)
 }
 EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);
 
+static inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp)
+{
+        return  min(tp->snd_ssthresh, tp->snd_cwnd-1);
+}
+
 static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 {
         struct tcp_sock *tp = tcp_sk(sk);
@@ -221,11 +226,10 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
                          */
                         diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
 
-                        if (diff > gamma && tp->snd_ssthresh > 2 ) {
+                        if (diff > gamma && tp->snd_cwnd <= tp->snd_ssthresh) {
                                 /* Going too fast. Time to slow down
                                  * and switch to congestion avoidance.
                                  */
-                                tp->snd_ssthresh = 2;
 
                                 /* Set cwnd to match the actual rate
                                  * exactly:
@@ -235,6 +239,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
                                  * utilization.
                                  */
                                 tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
+                                tp->snd_ssthresh = tcp_vegas_ssthresh(tp);
 
                         } else if (tp->snd_cwnd <= tp->snd_ssthresh) {
                                 /* Slow start.  */
@@ -250,6 +255,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
                                          * we slow down.
                                          */
                                         tp->snd_cwnd--;
+                                        tp->snd_ssthresh
+                                                = tcp_vegas_ssthresh(tp);
                                 } else if (diff < alpha) {
                                         /* We don't have enough extra packets
                                          * in the network, so speed up.