Re: [PATCH] make _minimum_ TCP retransmission timeout configurable take 2

[David Miller]

From: Rick Jones <[EMAIL PROTECTED]>
Date: Thu, 30 Aug 2007 18:07:13 -0700

> Anyhow, I'll try grubbing around the source code (already doing that to 
> see about writing a pet tcp cong module) but if pointers to the likely 
> relevant files were available I could try to help thrash-out the routing 
> metric version.  Like I said the consumers of this are a triffle well, 
> "anxious" :)

The change is actually a lot simpler than the sysctl version.

In fact it borders on trivial :-)

Signed-off-by: David S. Miller <[EMAIL PROTECTED]>

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index c91476c..dff3192 100644
--- 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 9785df3..1ee7212 100644
--- 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;
        }
 }


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