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 <gerrit@xxxxxxxxxxxxxx>
Acked-by: Ian McDonald <ian.mcdonald@xxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 13 ++++++-------
1 files changed, 6 insertions(+), 7 deletions(-)
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index a20b636..9d661e4 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -469,28 +469,29 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
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(struct sock *sk, struct sk_buff *skb)
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)
--
1.5.0.6
-
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