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/options.c b/net/dccp/options.c
index 4973bad..bfda087 100644
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -529,7 +529,7 @@
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 @@
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;