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Commit 59b80802 authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

dccp: make implementation of Syn-RTT symmetric 



This patch is thanks to Andre Noll who reported the issue and helped testing.

The Syn-RTT sampled during the initial handshake currently only works for
the client sending the DCCP-Request. TFRC penalizes the absence of an RTT
sample with a very slow initial speed (1 packet per second), which delays
slow-start significantly, resulting in sluggish performance.

This patch mirrors the "Syn RTT" principle by adding a timestamp also onto
the DCCP-Response, producing an RTT sample  when the (Data)Ack completing
the handshake arrives.

Also changed the documentation to 'TFRC' since Syn RTTs are also used by CCID-4.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a7d13fbf

net/dccp/input.c

+11 −2
Original line number Diff line number Diff line
@@ -430,7 +430,7 @@ static int dccp_rcv_request_sent_state_process(struct sock *sk, 
		if (dccp_parse_options(sk, NULL, skb))

			return 1;



		/* Obtain usec RTT sample from SYN exchange (used by CCID 3) */

		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */

		if (likely(dp->dccps_options_received.dccpor_timestamp_echo))

			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * (tstamp -

			    dp->dccps_options_received.dccpor_timestamp_echo));
@@ -535,6 +535,8 @@ static int dccp_rcv_respond_partopen_state_process(struct sock *sk, 
						   const struct dccp_hdr *dh,

						   const unsigned len)

{

	struct dccp_sock *dp = dccp_sk(sk);

	u32 sample = dp->dccps_options_received.dccpor_timestamp_echo;

	int queued = 0;



	switch (dh->dccph_type) {
@@ -559,7 +561,14 @@ static int dccp_rcv_respond_partopen_state_process(struct sock *sk, 
		if (sk->sk_state == DCCP_PARTOPEN)

			inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);



		dccp_sk(sk)->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq;

		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */

		if (likely(sample)) {

			long delta = dccp_timestamp() - sample;



			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * delta);

		}



		dp->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq;

		dccp_set_state(sk, DCCP_OPEN);



		if (dh->dccph_type == DCCP_PKT_DATAACK ||

net/dccp/options.c

+5 −1
Original line number Diff line number Diff line
@@ -529,7 +529,7 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb) 
		if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_REQUEST) {

			/*

			 * Obtain RTT sample from Request/Response exchange.

			 * This is currently used in CCID 3 initialisation.

			 * This is currently used for TFRC initialisation.

			 */

			if (dccp_insert_option_timestamp(skb))

				return -1;
@@ -562,6 +562,10 @@ int dccp_insert_options_rsk(struct dccp_request_sock *dreq, struct sk_buff *skb) 
	if (dccp_feat_insert_opts(NULL, dreq, skb))

		return -1;



	/* Obtain RTT sample from Response/Ack exchange (used by TFRC). */

	if (dccp_insert_option_timestamp(skb))

		return -1;



	if (dreq->dreq_timestamp_echo != 0 &&

	    dccp_insert_option_timestamp_echo(NULL, dreq, skb))

		return -1;