diff options
| -rw-r--r-- | net/dccp/ccids/Kconfig | 33 | ||||
| -rw-r--r-- | net/dccp/ccids/ccid3.c | 21 |
2 files changed, 46 insertions, 8 deletions
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig index dac89166eb1..80f46988769 100644 --- a/net/dccp/ccids/Kconfig +++ b/net/dccp/ccids/Kconfig @@ -89,4 +89,37 @@ config IP_DCCP_CCID3_DEBUG parameter to 0 or 1. If in doubt, say N. + +config IP_DCCP_CCID3_RTO + int "Use higher bound for nofeedback timer" + default 100 + depends on IP_DCCP_CCID3 && EXPERIMENTAL + ---help--- + Use higher lower bound for nofeedback timer expiration. + + The TFRC nofeedback timer normally expires after the maximum of 4 + RTTs and twice the current send interval (RFC 3448, 4.3). On LANs + with a small RTT this can mean a high processing load and reduced + performance, since then the nofeedback timer is triggered very + frequently. + + This option enables to set a higher lower bound for the nofeedback + value. Values in units of milliseconds can be set here. + + A value of 0 disables this feature by enforcing the value specified + in RFC 3448. The following values have been suggested as bounds for + experimental use: + * 16-20ms to match the typical multimedia inter-frame interval + * 100ms as a reasonable compromise [default] + * 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4) + + The default of 100ms is a compromise between a large value for + efficient DCCP implementations, and a small value to avoid disrupting + the network in times of congestion. + + The purpose of the nofeedback timer is to slow DCCP down when there + is serious network congestion: experimenting with larger values should + therefore not be performed on WANs. + + endmenu diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c index 70ebe705eb7..99807783a22 100644 --- a/net/dccp/ccids/ccid3.c +++ b/net/dccp/ccids/ccid3.c @@ -245,9 +245,10 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) } /* * Schedule no feedback timer to expire in - * max(4 * R, 2 * s/X) = max(4 * R, 2 * t_ipi) + * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi) + * See comments in packet_recv() regarding the value of t_RTO. */ - t_nfb = max(4 * hctx->ccid3hctx_rtt, 2 * hctx->ccid3hctx_t_ipi); + t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi); break; case TFRC_SSTATE_NO_SENT: DCCP_BUG("Illegal %s state NO_SENT, sk=%p", dccp_role(sk), sk); @@ -512,16 +513,20 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) */ sk->sk_write_space(sk); - /* Update timeout interval. We use the alternative variant of - * [RFC 3448, 3.1] which sets the upper bound of t_rto to one - * second, as it is suggested for TCP (see RFC 2988, 2.4). */ + /* + * Update timeout interval for the nofeedback timer. + * We use a configuration option to increase the lower bound. + * This can help avoid triggering the nofeedback timer too often + * ('spinning') on LANs with small RTTs. + */ hctx->ccid3hctx_t_rto = max_t(u32, 4 * hctx->ccid3hctx_rtt, - USEC_PER_SEC ); + CONFIG_IP_DCCP_CCID3_RTO * + (USEC_PER_SEC/1000) ); /* * Schedule no feedback timer to expire in - * max(4 * R, 2 * s/X) = max(4 * R, 2 * t_ipi) + * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi) */ - t_nfb = max(4 * hctx->ccid3hctx_rtt, 2 * hctx->ccid3hctx_t_ipi); + t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi); ccid3_pr_debug("%s, sk=%p, Scheduled no feedback timer to " "expire in %lu jiffies (%luus)\n", |