[PATCH 0/2] dccp: fix slow slow-start by symmetric Syn-RTT

[PATCH 0/2] dccp: fix slow slow-start by symmetric Syn-RTT

[Gerrit Renker]

This changeset fixes slow startup behaviour for DCCP streaming via
CCID-3/4 when a listening server needs to start streaming.

Patch #1: removes an unused 'sk' argument from several functions,
          it is used by patch #2;

Patch #2: fixes the sluggish slow-start problem by taking an RTT
          sample from the initial handshake also for listeing servers.

[PATCH 1/2] dccp: remove unused function argument

[Gerrit Renker]

This removes an unused 'sk' argument from several option-inserting functions.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/ackvec.c      |    2 +-
 net/dccp/ccids/ccid3.c |    4 ++--
 net/dccp/dccp.h        |   12 ++++--------
 net/dccp/options.c     |   14 ++++++--------
 4 files changed, 13 insertions(+), 19 deletions(-)

--- a/net/dccp/ackvec.c
+++ b/net/dccp/ackvec.c
@@ -82,7 +82,7 @@ int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb)
 	elapsed_time = delta / 10;
 
 	if (elapsed_time != 0 &&
-	    dccp_insert_option_elapsed_time(sk, skb, elapsed_time))
+	    dccp_insert_option_elapsed_time(skb, elapsed_time))
 		return -1;
 
 	avr = dccp_ackvec_record_new();
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -715,9 +715,9 @@ static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb)
 	x_recv = htonl(hc->rx_x_recv);
 	pinv   = htonl(hc->rx_pinv);
 
-	if (dccp_insert_option(sk, skb, TFRC_OPT_LOSS_EVENT_RATE,
+	if (dccp_insert_option(skb, TFRC_OPT_LOSS_EVENT_RATE,
 			       &pinv, sizeof(pinv)) ||
-	    dccp_insert_option(sk, skb, TFRC_OPT_RECEIVE_RATE,
+	    dccp_insert_option(skb, TFRC_OPT_RECEIVE_RATE,
 			       &x_recv, sizeof(x_recv)))
 		return -1;
 
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -446,16 +446,12 @@ extern void dccp_feat_list_purge(struct list_head *fn_list);
 
 extern int dccp_insert_options(struct sock *sk, struct sk_buff *skb);
 extern int dccp_insert_options_rsk(struct dccp_request_sock*, struct sk_buff*);
-extern int dccp_insert_option_elapsed_time(struct sock *sk,
-					    struct sk_buff *skb,
-					    u32 elapsed_time);
+extern int dccp_insert_option_elapsed_time(struct sk_buff *skb, u32 elapsed);
 extern u32 dccp_timestamp(void);
 extern void dccp_timestamping_init(void);
-extern int dccp_insert_option_timestamp(struct sock *sk,
-					 struct sk_buff *skb);
-extern int dccp_insert_option(struct sock *sk, struct sk_buff *skb,
-			       unsigned char option,
-			       const void *value, unsigned char len);
+extern int dccp_insert_option_timestamp(struct sk_buff *skb);
+extern int dccp_insert_option(struct sk_buff *skb, unsigned char option,
+			      const void *value, unsigned char len);
 
 #ifdef CONFIG_SYSCTL
 extern int dccp_sysctl_init(void);
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -299,9 +299,8 @@ static inline u8 dccp_ndp_len(const u64 ndp)
 	return likely(ndp <= USHRT_MAX) ? 2 : (ndp <= UINT_MAX ? 4 : 6);
 }
 
-int dccp_insert_option(struct sock *sk, struct sk_buff *skb,
-			const unsigned char option,
-			const void *value, const unsigned char len)
+int dccp_insert_option(struct sk_buff *skb, const unsigned char option,
+		       const void *value, const unsigned char len)
 {
 	unsigned char *to;
 
@@ -354,8 +353,7 @@ static inline int dccp_elapsed_time_len(const u32 elapsed_time)
 	return elapsed_time == 0 ? 0 : elapsed_time <= 0xFFFF ? 2 : 4;
 }
 
-int dccp_insert_option_elapsed_time(struct sock *sk, struct sk_buff *skb,
-				    u32 elapsed_time)
+int dccp_insert_option_elapsed_time(struct sk_buff *skb, u32 elapsed_time)
 {
 	const int elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
 	const int len = 2 + elapsed_time_len;
@@ -386,13 +384,13 @@ int dccp_insert_option_elapsed_time(struct sock *sk, struct sk_buff *skb,
 
 EXPORT_SYMBOL_GPL(dccp_insert_option_elapsed_time);
 
-int dccp_insert_option_timestamp(struct sock *sk, struct sk_buff *skb)
+int dccp_insert_option_timestamp(struct sk_buff *skb)
 {
 	__be32 now = htonl(dccp_timestamp());
 	/* yes this will overflow but that is the point as we want a
 	 * 10 usec 32 bit timer which mean it wraps every 11.9 hours */
 
-	return dccp_insert_option(sk, skb, DCCPO_TIMESTAMP, &now, sizeof(now));
+	return dccp_insert_option(skb, DCCPO_TIMESTAMP, &now, sizeof(now));
 }
 
 EXPORT_SYMBOL_GPL(dccp_insert_option_timestamp);
@@ -533,7 +531,7 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
 			 * Obtain RTT sample from Request/Response exchange.
 			 * This is currently used in CCID 3 initialisation.
 			 */
-			if (dccp_insert_option_timestamp(sk, skb))
+			if (dccp_insert_option_timestamp(skb))
 				return -1;
 
 		} else if (dp->dccps_hc_rx_ackvec != NULL &&
-- 
1.6.0.rc2

[PATCH 2/2] dccp: make implementation of Syn-RTT symmetric

[Gerrit Renker]

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: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/input.c   |   13 +++++++++++--
 net/dccp/options.c |    6 +++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -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 ||
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -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;
-- 
1.6.0.rc2

Re: [PATCH 0/2] dccp: fix slow slow-start by symmetric Syn-RTT

[David Miller]

From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Tue, 22 Jun 2010 13:14:33 +0200

> This changeset fixes slow startup behaviour for DCCP streaming via
> CCID-3/4 when a listening server needs to start streaming.
> 
> Patch #1: removes an unused 'sk' argument from several functions,
>           it is used by patch #2;
> 
> Patch #2: fixes the sluggish slow-start problem by taking an RTT
>           sample from the initial handshake also for listeing servers.

Both applied to net-next-2.6, thanks!