[CCID 3]: Use skb timestamp for TX side 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 <gerrit@xxxxxxxxxxxxxx> --- net/dccp/ccids/ccid3.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/dccp/ccids/ccid3.c +++ b/net/dccp/ccids/ccid3.c @@ -469,7 +469,7 @@ static void ccid3_hc_tx_packet_recv(stru 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 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 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); - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
