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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2010-08-29 15:23:14 -0400
committerDavid S. Miller <davem@davemloft.net>2010-08-30 16:45:28 -0400
commit89858ad14307a398961a0f1414b04053c1475e4f (patch)
tree860eca4c0fb4c9c470d407407ba051ae814c9dfa /net
parent4886fcad6e12572afbd230dfab1b268eace20d6d (diff)
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>
Diffstat (limited to 'net')
-rw-r--r--net/dccp/ccids/Kconfig31
-rw-r--r--net/dccp/ccids/ccid3.c11
-rw-r--r--net/dccp/ccids/ccid3.h2
3 files changed, 6 insertions, 38 deletions
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig
index 8408398cd44e..0581143cb800 100644
--- a/net/dccp/ccids/Kconfig
+++ b/net/dccp/ccids/Kconfig
@@ -47,37 +47,6 @@ config IP_DCCP_CCID3_DEBUG
47 47
48 If in doubt, say N. 48 If in doubt, say N.
49 49
50config IP_DCCP_CCID3_RTO
51 int "Use higher bound for nofeedback timer"
52 default 100
53 depends on IP_DCCP_CCID3 && EXPERIMENTAL
54 ---help---
55 Use higher lower bound for nofeedback timer expiration.
56
57 The TFRC nofeedback timer normally expires after the maximum of 4
58 RTTs and twice the current send interval (RFC 3448, 4.3). On LANs
59 with a small RTT this can mean a high processing load and reduced
60 performance, since then the nofeedback timer is triggered very
61 frequently.
62
63 This option enables to set a higher lower bound for the nofeedback
64 value. Values in units of milliseconds can be set here.
65
66 A value of 0 disables this feature by enforcing the value specified
67 in RFC 3448. The following values have been suggested as bounds for
68 experimental use:
69 * 16-20ms to match the typical multimedia inter-frame interval
70 * 100ms as a reasonable compromise [default]
71 * 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4)
72
73 The default of 100ms is a compromise between a large value for
74 efficient DCCP implementations, and a small value to avoid disrupting
75 the network in times of congestion.
76
77 The purpose of the nofeedback timer is to slow DCCP down when there
78 is serious network congestion: experimenting with larger values should
79 therefore not be performed on WANs.
80
81config IP_DCCP_TFRC_LIB 50config IP_DCCP_TFRC_LIB
82 def_bool y if IP_DCCP_CCID3 51 def_bool y if IP_DCCP_CCID3
83 52
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 4340672a817c..278e17069322 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -460,13 +460,12 @@ done_computing_x:
460 sk->sk_write_space(sk); 460 sk->sk_write_space(sk);
461 461
462 /* 462 /*
463 * Update timeout interval for the nofeedback timer. 463 * Update timeout interval for the nofeedback timer. In order to control
464 * We use a configuration option to increase the lower bound. 464 * rate halving on networks with very low RTTs (<= 1 ms), use per-route
465 * This can help avoid triggering the nofeedback timer too 465 * tunable RTAX_RTO_MIN value as the lower bound.
466 * often ('spinning') on LANs with small RTTs.
467 */ 466 */
468 hc->tx_t_rto = max_t(u32, 4 * hc->tx_rtt, (CONFIG_IP_DCCP_CCID3_RTO * 467 hc->tx_t_rto = max_t(u32, 4 * hc->tx_rtt,
469 (USEC_PER_SEC / 1000))); 468 USEC_PER_SEC/HZ * tcp_rto_min(sk));
470 /* 469 /*
471 * Schedule no feedback timer to expire in 470 * Schedule no feedback timer to expire in
472 * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi) 471 * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi)
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h
index b1864243be07..b7e569c22f36 100644
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -42,7 +42,7 @@
42#include "lib/tfrc.h" 42#include "lib/tfrc.h"
43#include "../ccid.h" 43#include "../ccid.h"
44 44
45/* Two seconds as per RFC 3448 4.2 */ 45/* Two seconds as per RFC 5348, 4.2 */
46#define TFRC_INITIAL_TIMEOUT (2 * USEC_PER_SEC) 46#define TFRC_INITIAL_TIMEOUT (2 * USEC_PER_SEC)
47 47
48/* In usecs - half the scheduling granularity as per RFC3448 4.6 */ 48/* In usecs - half the scheduling granularity as per RFC3448 4.6 */