dccp ccid-3: use per-route RTO or TCP RTO as fallback

This makes RTAX_RTO_MIN also available to CCID-3, replacing the compile-time
RTO lower bound with a per-route tunable value.

The original Kconfig option solved the problem that a very low RTT (in the
order of HZ) can trigger too frequent and unnecessary reductions of the
sending rate.

This tunable does not affect the initial RTO value of 2 seconds specified in
RFC 5348, section 4.2 and Appendix B. But like the hardcoded Kconfig value,
it allows to adapt to network conditions.

The same effect as the original Kconfig option of 100ms is now achieved by

> ip route replace to unicast 192.168.0.0/24 rto_min 100j dev eth0

(assuming HZ=1000).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index cdb64922ba10..271d524a4c8d 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -174,6 +174,9 @@ Per-route rto_min support
                 > ip route change 10.0.0.0/24   rto_min 250j dev wlan0
                 > ip route add    10.0.0.254/32 rto_min 800j dev wlan0
                 > ip route show dev wlan0
+        CCID-3 also supports the rto_min setting: it is used to define the lower
+        bound for the expiry of the nofeedback timer. This can be useful on LANs
+        with very low RTTs (e.g., loopback, Gbit ethernet).
 
 
 Notes