[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>
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 32c2e9d..6ae2fef 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -180,13 +180,20 @@
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