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dccp: make implementation of Syn-RTT symmetric

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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>
This commit is contained in:
Gerrit Renker 2010-06-22 01:14:35 +00:00 • committed by David S. Miller
parent a7d13fbf85
commit 59b80802a8
2 changed files with 16 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

13
net/dccp/input.c
View file

@ -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 ||