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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2010-08-29 19:23:13 +0000
committerDavid S. Miller <davem@davemloft.net>2010-08-30 13:45:27 -0700
commit4886fcad6e12572afbd230dfab1b268eace20d6d (patch)
treec0ac7dc930a8de315083ec3882ff78a325747e70
parent22b71c8f4f3db8df92f5e7b081c265bc56c0bd2f (diff)
dccp ccid-2: Share TCP's minimum RTO code
Using a fixed RTO_MIN of 0.2 seconds was found to cause problems for CCID-2 over 802.11g: at least once per session there was a spurious timeout. It helped to then increase the the value of RTO_MIN over this link. Since the problem is the same as in TCP, this patch makes the solution from commit "05bb1fad1cde025a864a90cfeb98dcbefe78a44a" "[TCP]: Allow minimum RTO to be configurable via routing metrics." available to DCCP. This avoids reinventing the wheel, so that e.g. the following works in the expected way now also for CCID-2: > ip route change 10.0.0.2 rto_min 800 dev ath0 Luckily this useful rto_min function was recently moved to net/tcp.h, which simplifies sharing code originating from TCP. Documentation also updated (plus minor whitespace fixes). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--Documentation/networking/dccp.txt26
-rw-r--r--net/dccp/ccids/ccid2.c5
2 files changed, 23 insertions, 8 deletions
diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index a62fdf7a6bff..cdb64922ba10 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -1,18 +1,20 @@
DCCP protocol
-============
+=============
Contents
========
-
- Introduction
- Missing features
- Socket options
+- Sysctl variables
+- IOCTLs
+- Other tunables
- Notes
+
Introduction
============
-
Datagram Congestion Control Protocol (DCCP) is an unreliable, connection
oriented protocol designed to solve issues present in UDP and TCP, particularly
for real-time and multimedia (streaming) traffic.
@@ -29,9 +31,9 @@ It has a base protocol and pluggable congestion control IDs (CCIDs).
DCCP is a Proposed Standard (RFC 2026), and the homepage for DCCP as a protocol
is at http://www.ietf.org/html.charters/dccp-charter.html
+
Missing features
================
-
The Linux DCCP implementation does not currently support all the features that are
specified in RFCs 4340...42.
@@ -45,7 +47,6 @@ http://linux-net.osdl.org/index.php/DCCP_Testing#Experimental_DCCP_source_tree
Socket options
==============
-
DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
the socket will fall back to 0 (which means that no meaningful service code
@@ -112,6 +113,7 @@ DCCP_SOCKOPT_CCID_TX_INFO
On unidirectional connections it is useful to close the unused half-connection
via shutdown (SHUT_WR or SHUT_RD): this will reduce per-packet processing costs.
+
Sysctl variables
================
Several DCCP default parameters can be managed by the following sysctls
@@ -155,15 +157,27 @@ sync_ratelimit = 125 ms
sequence-invalid packets on the same socket (RFC 4340, 7.5.4). The unit
of this parameter is milliseconds; a value of 0 disables rate-limiting.
+
IOCTLS
======
FIONREAD
Works as in udp(7): returns in the `int' argument pointer the size of
the next pending datagram in bytes, or 0 when no datagram is pending.
+
+Other tunables
+==============
+Per-route rto_min support
+ CCID-2 supports the RTAX_RTO_MIN per-route setting for the minimum value
+ of the RTO timer. This setting can be modified via the 'rto_min' option
+ of iproute2; for example:
+ > 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
+
+
Notes
=====
-
DCCP does not travel through NAT successfully at present on many boxes. This is
because the checksum covers the pseudo-header as per TCP and UDP. Linux NAT
support for DCCP has been added.
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index b9c942a09c98..dc18172b1e59 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -325,8 +325,9 @@ static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
hc->tx_srtt = m << 3;
hc->tx_mdev = m << 1;
- hc->tx_mdev_max = max(TCP_RTO_MIN, hc->tx_mdev);
+ hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
hc->tx_rttvar = hc->tx_mdev_max;
+
hc->tx_rtt_seq = dccp_sk(sk)->dccps_gss;
} else {
/* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
@@ -367,7 +368,7 @@ static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
hc->tx_rttvar -= (hc->tx_rttvar -
hc->tx_mdev_max) >> 2;
hc->tx_rtt_seq = dccp_sk(sk)->dccps_gss;
- hc->tx_mdev_max = TCP_RTO_MIN;
+ hc->tx_mdev_max = tcp_rto_min(sk);
}
}