This patch uses skb timestamps (and provides the necessary enable/disable
mechanism) instead of layer-4 timestamping. This affords a more accurate
RTT estimation.
Background:
The sender currently computes the timestamp of received (Ack) packets when
the packet is delivered to layer 4. The skb timestamp is taken earlier, and
the differences are notable: dDuring test runs under different load conditions,
the layer-4 timestamp was observed to be on average up to 100 microseconds,
in the extreme up to a millisecond, later than the skb timestamp.
This has a negative impact on the RTT estimation (reduced accuracy).
Signed-off-by: Gerrit Renker <[EMAIL PROTECTED]>
Acked-by: Ian McDonald <[EMAIL PROTECTED]>
Signed-off-by: Arnaldo Carvalho de Melo <[EMAIL PROTECTED]>
---
net/dccp/ccids/ccid3.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index b756e95..a20b636 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -469,7 +469,7 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct
sk_buff *skb)
else /* can not exceed 100% */
hctx->ccid3hctx_p = 1000000 / pinv;
- do_gettimeofday(&now);
+ skb_get_timestamp(skb, &now);
/*
* Calculate new round trip sample as per [RFC 3448, 4.3] by
@@ -645,6 +645,7 @@ static int ccid3_hc_tx_init(struct ccid *ccid, struct sock
*sk)
ccid3_hc_tx_no_feedback_timer;
hctx->ccid3hctx_no_feedback_timer.data = (unsigned long)sk;
init_timer(&hctx->ccid3hctx_no_feedback_timer);
+ net_enable_timestamp();
return 0;
}
@@ -657,6 +658,7 @@ static void ccid3_hc_tx_exit(struct sock *sk)
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_TERM);
sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);
+ net_disable_timestamp();
/* Empty packet history */
dccp_tx_hist_purge(ccid3_tx_hist, &hctx->ccid3hctx_hist);
--
1.5.0.6
-
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