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Commit d20ed95f authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp tfrc: Perform early loss detection 



This enables the TFRC code to begin loss detection (as soon as the module
is loaded), using the latest updates from rfc3448bis-06, 6.3.1:

 * when the first data packet(s) are lost or marked, set
 * X_target = s/(2*R) => f(p) = s/(R * X_target) = 2,
 * corresponding to a loss rate of ~ 20.64%.

The handle_loss() function is now called right at the begin of rx_packet_recv()
and thus no longer protected against duplicates: hence a call to rx_duplicate()
has been added.  Such a call makes sense now, as the previous patch initialises
the first entry with a sequence number of GSR.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 24b8d343

net/dccp/ccids/ccid3.c

+39 −9
Original line number Diff line number Diff line
@@ -577,6 +577,28 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk, 
		hcrx->p_inverse = ~0U;   /* see RFC 4342, 8.5 */

		break;

	case CCID3_FBACK_PARAM_CHANGE:

		if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA)) {

			/*

			 * rfc3448bis-06, 6.3.1: First packet(s) lost or marked

			 * FIXME: in rfc3448bis the receiver returns X_recv=0

			 * here as it normally would in the first feedback packet.

			 * However this is not possible yet, since the code still

			 * uses RFC 3448, i.e.

			 *    If (p > 0)

			 *      Calculate X_calc using the TCP throughput equation.

			 *      X = max(min(X_calc, 2*X_recv), s/t_mbi);

			 * would bring X down to s/t_mbi. That is why we return

			 * X_recv according to rfc3448bis-06 for the moment.

			 */

			u32 rtt = hcrx->rtt ? : DCCP_FALLBACK_RTT, s = hcrx->s;



			if (s == 0) {

				DCCP_WARN("No sample for s, using fallback\n");

				s = TCP_MIN_RCVMSS;

			}

			hcrx->x_recv = scaled_div32(s, 2 * rtt);

			break;

		}

		/*

		 * When parameters change (new loss or p > p_prev), we do not

		 * have a reliable estimate for R_m of [RFC 3448, 6.2] and so
@@ -650,6 +672,14 @@ static u32 ccid3_first_li(struct sock *sk) 
	u32 x_recv, p, delta;

	u64 fval;



	/*

	 * rfc3448bis-06, 6.3.1: First data packet(s) are marked or lost. Set p

	 * to give the equivalent of X_target = s/(2*R). Thus fval = 2 and so p

	 * is about 20.64%. This yields an interval length of 4.84 (rounded up).

	 */

	if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA))

		return 5;



	if (hcrx->rtt == 0) {

		DCCP_WARN("No RTT estimate available, using fallback RTT\n");

		hcrx->rtt = DCCP_FALLBACK_RTT;
@@ -683,6 +713,15 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb) 
	const u64 ndp = dccp_sk(sk)->dccps_options_received.dccpor_ndp;

	const bool is_data_packet = dccp_data_packet(skb);



	/*

	 * Perform loss detection and handle pending losses

	 */

	if (tfrc_rx_handle_loss(&hcrx->hist, &hcrx->li_hist,

				skb, ndp, ccid3_first_li, sk)) {

		do_feedback = CCID3_FBACK_PARAM_CHANGE;

		goto done_receiving;

	}



	if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA)) {

		if (is_data_packet) {

			const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
@@ -710,15 +749,6 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		hcrx->bytes_recv += payload;

	}



	/*

	 * Perform loss detection and handle pending losses

	 */

	if (tfrc_rx_handle_loss(&hcrx->hist, &hcrx->li_hist,

				skb, ndp, ccid3_first_li, sk)) {

		do_feedback = CCID3_FBACK_PARAM_CHANGE;

		goto done_receiving;

	}



	if (tfrc_rx_hist_loss_pending(&hcrx->hist))

		return; /* done receiving */

net/dccp/ccids/lib/packet_history.c

+3 −0
Original line number Diff line number Diff line
@@ -335,6 +335,9 @@ int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, 
{

	int is_new_loss = 0;



	if (tfrc_rx_hist_duplicate(h, skb))

		return 0;



	if (h->loss_count == 0) {

		__do_track_loss(h, skb, ndp);

	} else if (h->loss_count == 1) {