[DCCP]: Use higher RTO default for CCID3 (8a508ac2) · Commits · 戴 / test

net/dccp/ccids/Kconfig

+33 −0

Original line number	Diff line number	Diff line
		@@ -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

net/dccp/ccids/ccid3.c

+13 −8

Original line number	Diff line number	Diff line
		@@ -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",

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