[TCP] FRTO: Update sysctl documentation

Since the SACK enhanced FRTO was added, the code has been
under test numerous times so remove "experimental" claim
from the documentation. Also be a bit more verbose about
the usage.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 5 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 32c2e9da5f3a..6ae2feff3087 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -180,13 +180,20 @@ tcp_fin_timeout - INTEGER
         to live longer. Cf. tcp_max_orphans.
 
 tcp_frto - INTEGER
-        Enables F-RTO, an enhanced recovery algorithm for TCP retransmission
+        Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
+        F-RTO is an enhanced recovery algorithm for TCP retransmission
         timeouts.  It is particularly beneficial in wireless environments
         where packet loss is typically due to random radio interference
-        rather than intermediate router congestion. If set to 1, basic
-        version is enabled. 2 enables SACK enhanced F-RTO, which is
-        EXPERIMENTAL. The basic version can be used also when SACK is
-        enabled for a flow through tcp_sack sysctl.
+        rather than intermediate router congestion.  FRTO is sender-side
+        only modification.  Therefore it does not require any support from
+        the peer, but in a typical case, however, where wireless link is
+        the local access link and most of the data flows downlink, the
+        faraway servers should have FRTO enabled to take advantage of it.
+        If set to 1, basic version is enabled.  2 enables SACK enhanced
+        F-RTO if flow uses SACK.  The basic version can be used also when
+        SACK is in use though scenario(s) with it exists where FRTO
+        interacts badly with the packet counting of the SACK enabled TCP
+        flow.
 
 tcp_frto_response - INTEGER
         When F-RTO has detected that a TCP retransmission timeout was