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: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/input.c b/net/dccp/input.c
index 6beb6a7..10c957a 100644
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -430,7 +430,7 @@
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 @@
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 @@
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 ||