From 8a508ac26e72aa203677aa6a8464bd3ea44216a6 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Sun, 3 Dec 2006 14:50:23 -0200 Subject: [DCCP]: Use higher RTO default for CCID3 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 patch provides a configuration option to set the bound for the nofeedback timer, using as default 100 milliseconds. By setting the configuration option to 0, strict RFC 3448 behaviour can be enforced for the nofeedback timer. Signed-off-by: Gerrit Renker Signed-off-by: Arnaldo Carvalho de Melo --- net/dccp/ccids/ccid3.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) (limited to 'net/dccp/ccids/ccid3.c') diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c index 70ebe70..9980778 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", -- cgit v1.1