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: Honour initial RTT estimate

PATCH In review Gerrit Renker 2 participants 2 messages Mar 21, 2007 – Mar 26, 2007 Networking

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Gerrit Renker

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#0 lore raw

PATCH 8/25 : Honour initial RTT estimate

[CCID 3]: Honour initial RTT estimate

This is a small optimisation which improves the accuracy of TX RTT sampling when an initial RTT sample (e.g. from the intial Request/Response exchange) is available.

Signed-off-by Gerrit Renker <[email protected]>
---
 net/dccp/ccids/ccid3.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)
net/dccp/ccids/ccid3.c +6 -7
@@ -469,28 +469,29 @@ static void ccid3_hc_tx_packet_recv(stru
 		else				       /* can not exceed 100% */
 			hctx->ccid3hctx_p = 1000000 / pinv;
 
-		skb_get_timestamp(skb, &now);
-
 		/*
 		 * Calculate new round trip sample as per [RFC 3448, 4.3] by
 		 *	R_sample  =  (now - t_recvdata) - t_elapsed
 		 */
+		skb_get_timestamp(skb, &now);
 		r_sample = dccp_sample_rtt(sk, &now, &packet->dccphtx_tstamp);
 
 		/*
-		 * Update RTT estimate by
-		 * If (No feedback recv)
+		 * Update RTT estimate (honours RTT from SYN exchange):
+		 * If (No RTT sample so far)
 		 *    R = R_sample;
 		 * Else
 		 *    R = q * R + (1 - q) * R_sample;
 		 *
 		 * q is a constant, RFC 3448 recomments 0.9
 		 */
+		hctx->ccid3hctx_rtt = hctx->ccid3hctx_rtt = 0 ?  r_sample
+				    : (9 * hctx->ccid3hctx_rtt + r_sample) / 10;
+
 		if (hctx->ccid3hctx_state = TFRC_SSTATE_NO_FBACK) {
 			/*
 			 * Larger Initial Windows [RFC 4342, sec. 5]
 			 */
-			hctx->ccid3hctx_rtt  = r_sample;
 			hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
 			hctx->ccid3hctx_t_ld = now;
 

@@ -504,8 +505,6 @@ static void ccid3_hc_tx_packet_recv(stru
 
 			ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
 		} else {
-			hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +
-						   r_sample) / 10;
 
 			/* Update sending rate (step 4 of [RFC 3448, 4.3]) */
 			if (hctx->ccid3hctx_p > 0)
Acked-by on v1 8/25
#1 lore raw
Quoted 14 lines · Gerrit Renker

[CCID 3]: Honour initial RTT estimate

This is a small optimisation which improves the accuracy of TX RTT sampling when an initial RTT sample (e.g. from the intial Request/Response exchange) is available.

Signed-off-by Gerrit Renker <[email protected]>
---
 net/dccp/ccids/ccid3.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

net/dccp/ccids/ccid3.c static void ccid3_hc_tx_packet_recv(stru · line 476

Quoted 10 lines
net/dccp/ccids/ccid3.c +1 -2
@@ -469,28 +469,29 @@ static void ccid3_hc_tx_packet_recv(stru
                else                                   /* can not exceed 100% */
                        hctx->ccid3hctx_p = 1000000 / pinv;
 
-               skb_get_timestamp(skb, &now);
-
                /*
                 * Calculate new round trip sample as per [RFC 3448, 4.3] by
                 *      R_sample  =  (now - t_recvdata) - t_elapsed
                 */
+               skb_get_timestamp(skb, &now);

I can see how that optimises - shifting after the comment ;-)

Acked-by Ian McDonald <[email protected]>
Signature · 3 lines
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