[TCP]: Allow minimum RTO to be configurable via routing metrics.

Cell phone networks do link layer retransmissions and other
things that cause unnecessary timeout retransmits.  So allow
the minimum RTO to be inflated per-route to deal with this.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index c91476ce314ac32853cd8cac29859ad3790ee975..dff3192374f8f0af665715a12e309d471ae70b97 100644 (file)
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -351,6 +351,8 @@ enum
 #define RTAX_INITCWND RTAX_INITCWND
        RTAX_FEATURES,
 #define RTAX_FEATURES RTAX_FEATURES
+       RTAX_RTO_MIN,
+#define RTAX_RTO_MIN RTAX_RTO_MIN
        __RTAX_MAX
 };
 

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9785df37a65feeb285bc2f656eb828216de23585..1ee72127462bf37ed5ef834ebc71111b1cf070d5 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -555,6 +555,16 @@ static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
                tcp_grow_window(sk, skb);
 }
 
+static u32 tcp_rto_min(struct sock *sk)
+{
+       struct dst_entry *dst = __sk_dst_get(sk);
+       u32 rto_min = TCP_RTO_MIN;
+
+       if (dst_metric_locked(dst, RTAX_RTO_MIN))
+               rto_min = dst->metrics[RTAX_RTO_MIN-1];
+       return rto_min;
+}
+
 /* Called to compute a smoothed rtt estimate. The data fed to this
  * routine either comes from timestamps, or from segments that were
  * known _not_ to have been retransmitted [see Karn/Partridge
@@ -616,13 +626,13 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
                        if (tp->mdev_max < tp->rttvar)
                                tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
                        tp->rtt_seq = tp->snd_nxt;
-                       tp->mdev_max = TCP_RTO_MIN;
+                       tp->mdev_max = tcp_rto_min(sk);
                }
        } else {
                /* no previous measure. */
                tp->srtt = m<<3;        /* take the measured time to be rtt */
                tp->mdev = m<<1;        /* make sure rto = 3*rtt */
-               tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
+               tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
                tp->rtt_seq = tp->snd_nxt;
        }
 }