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Commit 2b81143a authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp ccid-3: Always perform receiver RTT sampling 

This updates the CCID-3 receiver in part with regard to errata 610 and 611
(http://www.rfc-editor.org/errata_list.php

), which change RFC 4342 to use the
Receive Rate as specified in rfc3448bis, requiring to constantly sample the
RTT (or use a sender RTT).

Doing this requires reusing the RX history structure after dealing with a loss.

The patch does not resolve how to compute X_recv if the interval is less
than 1 RTT. A FIXME has been added (and is resolved in subsequent patch).

Furthermore, since this is all TFRC-based functionality, the RTT estimation
is now also performed by the dccp_tfrc_lib module. This further simplifies
the CCID-3 code.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 2f3e3bba

net/dccp/ccids/ccid3.c

+14 −29
Original line number Diff line number Diff line
@@ -556,8 +556,8 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk, 
			 * 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	= tfrc_rx_hist_packet_size(&hcrx->hist);

			u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),

			    rtt = tfrc_rx_hist_rtt(&hcrx->hist);



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

			break;
@@ -576,6 +576,11 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk, 
			break;

		/* fall through */

	case CCID3_FBACK_PERIODIC:

		/*

		 * FIXME: check if delta is less than or equal to 1 RTT using

		 * the receiver RTT sample. This is described in Errata 610/611

		 * of RFC 4342 which reference section 6.2 of RFC 3448.

		 */

		delta = ktime_us_delta(now, hcrx->tstamp_last_feedback);

		if (delta <= 0)

			DCCP_BUG("delta (%ld) <= 0", (long)delta);
@@ -633,8 +638,8 @@ static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb) 
static u32 ccid3_first_li(struct sock *sk)

{

	struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);

	u32 x_recv, p, delta,

	    s = tfrc_rx_hist_packet_size(&hcrx->hist);

	u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),

	    rtt = tfrc_rx_hist_rtt(&hcrx->hist), x_recv, p, delta;

	u64 fval;



	/*
@@ -645,11 +650,6 @@ static u32 ccid3_first_li(struct sock *sk) 
	if (unlikely(hcrx->feedback == CCID3_FBACK_NONE))

		return 5;



	if (hcrx->rtt == 0) {

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

		hcrx->rtt = DCCP_FALLBACK_RTT;

	}



	delta = ktime_to_us(net_timedelta(hcrx->tstamp_last_feedback));

	x_recv = scaled_div32(hcrx->hist.bytes_recvd, delta);

	if (x_recv == 0) {		/* would also trigger divide-by-zero */
@@ -661,7 +661,7 @@ static u32 ccid3_first_li(struct sock *sk) 
		x_recv = hcrx->x_recv;

	}



	fval = scaled_div32(scaled_div(s, hcrx->rtt), x_recv);

	fval = scaled_div32(scaled_div(s, rtt), x_recv);

	p = tfrc_calc_x_reverse_lookup(fval);



	ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
@@ -695,26 +695,11 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb) 
	if (tfrc_rx_hist_loss_pending(&hcrx->hist))

		return; /* done receiving */



	/*

	 * Handle data packets: RTT sampling and monitoring p

	 */

	if (unlikely(!is_data_packet))

		goto update_records;



	if (!tfrc_lh_is_initialised(&hcrx->li_hist)) {

		const u32 sample = tfrc_rx_hist_sample_rtt(&hcrx->hist, skb);

		/*

		 * Empty loss history: no loss so far, hence p stays 0.

		 * Sample RTT values, since an RTT estimate is required for the

		 * computation of p when the first loss occurs; RFC 3448, 6.3.1.

		 */

		if (sample != 0)

			hcrx->rtt = tfrc_ewma(hcrx->rtt, sample, 9);

	}

	/*

	 * Check if the periodic once-per-RTT feedback is due; RFC 4342, 10.3

	 */

	if (SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->last_counter) > 3)

	if (is_data_packet &&

	    SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->last_counter) > 3)

		do_feedback = CCID3_FBACK_PERIODIC;



update_records:
@@ -744,7 +729,7 @@ static void ccid3_hc_rx_exit(struct sock *sk) 
static void ccid3_hc_rx_get_info(struct sock *sk, struct tcp_info *info)

{

	info->tcpi_options  |= TCPI_OPT_TIMESTAMPS;

	info->tcpi_rcv_rtt  = ccid3_hc_rx_sk(sk)->rtt;

	info->tcpi_rcv_rtt  = tfrc_rx_hist_rtt(&ccid3_hc_rx_sk(sk)->hist);

}



static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
@@ -759,7 +744,7 @@ static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len, 
		if (len < sizeof(rx_info))

			return -EINVAL;

		rx_info.tfrcrx_x_recv = hcrx->x_recv;

		rx_info.tfrcrx_rtt    = hcrx->rtt;

		rx_info.tfrcrx_rtt    = tfrc_rx_hist_rtt(&hcrx->hist);

		rx_info.tfrcrx_p      = tfrc_invert_loss_event_rate(hcrx->p_inverse);

		len = sizeof(rx_info);

		val = &rx_info;

net/dccp/ccids/ccid3.h

+0 −2
Original line number Diff line number Diff line
@@ -127,7 +127,6 @@ enum ccid3_fback_type { 
 *  @last_counter  -  Tracks window counter (RFC 4342, 8.1)

 *  @feedback  -  The type of the feedback last sent

 *  @x_recv  -  Receiver estimate of send rate (RFC 3448, sec. 4.3)

 *  @rtt  -  Receiver estimate of RTT

 *  @tstamp_last_feedback  -  Time at which last feedback was sent

 *  @hist  -  Packet history (loss detection + RTT sampling)

 *  @li_hist  -  Loss Interval database
@@ -137,7 +136,6 @@ struct ccid3_hc_rx_sock { 
	u8				last_counter:4;

	enum ccid3_fback_type		feedback:4;

	u32				x_recv;

	u32				rtt;

	ktime_t				tstamp_last_feedback;

	struct tfrc_rx_hist		hist;

	struct tfrc_loss_hist		li_hist;

net/dccp/ccids/lib/packet_history.c

+44 −16
Original line number Diff line number Diff line
@@ -151,14 +151,31 @@ int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb) 
}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_duplicate);





static void __tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)

{

	struct tfrc_rx_hist_entry *tmp = h->ring[a];



	h->ring[a] = h->ring[b];

	h->ring[b] = tmp;

}



static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)

{

	const u8 idx_a = tfrc_rx_hist_index(h, a),

		 idx_b = tfrc_rx_hist_index(h, b);

	struct tfrc_rx_hist_entry *tmp = h->ring[idx_a];

	__tfrc_rx_hist_swap(h, tfrc_rx_hist_index(h, a),

			       tfrc_rx_hist_index(h, b));

}



	h->ring[idx_a] = h->ring[idx_b];

	h->ring[idx_b] = tmp;

/**

 * tfrc_rx_hist_resume_rtt_sampling  -  Prepare RX history for RTT sampling

 * This is called after loss detection has finished, when the history entry

 * with the index of `loss_count' holds the highest-received sequence number.

 * RTT sampling requires this information at ring[0] (tfrc_rx_hist_sample_rtt).

 */

static inline void tfrc_rx_hist_resume_rtt_sampling(struct tfrc_rx_hist *h)

{

	__tfrc_rx_hist_swap(h, 0, tfrc_rx_hist_index(h, h->loss_count));

	h->loss_count = h->loss_start = 0;

}



/*
@@ -200,8 +217,7 @@ static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2 


		if (dccp_loss_free(s2, s1, n1)) {

			/* hole is filled: S0, S2, and S1 are consecutive */

			h->loss_count = 0;

			h->loss_start = tfrc_rx_hist_index(h, 1);

			tfrc_rx_hist_resume_rtt_sampling(h);

		} else

			/* gap between S2 and S1: just update loss_prev */

			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
@@ -254,8 +270,7 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3) 


			if (dccp_loss_free(s1, s2, n2)) {

				/* entire hole filled by S0, S3, S1, S2 */

				h->loss_start = tfrc_rx_hist_index(h, 2);

				h->loss_count = 0;

				tfrc_rx_hist_resume_rtt_sampling(h);

			} else {

				/* gap remains between S1 and S2 */

				h->loss_start = tfrc_rx_hist_index(h, 1);
@@ -299,8 +314,7 @@ static void __three_after_loss(struct tfrc_rx_hist *h) 


		if (dccp_loss_free(s2, s3, n3)) {

			/* no gap between S2 and S3: entire hole is filled */

			h->loss_start = tfrc_rx_hist_index(h, 3);

			h->loss_count = 0;

			tfrc_rx_hist_resume_rtt_sampling(h);

		} else {

			/* gap between S2 and S3 */

			h->loss_start = tfrc_rx_hist_index(h, 2);
@@ -340,6 +354,7 @@ int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, 


	if (h->loss_count == 0) {

		__do_track_loss(h, skb, ndp);

		tfrc_rx_hist_sample_rtt(h, skb);

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

		__one_after_loss(h, skb, ndp);

	} else if (h->loss_count != 2) {
@@ -435,9 +450,22 @@ static inline struct tfrc_rx_hist_entry * 
 * Based on ideas presented in RFC 4342, 8.1. Returns 0 if it was not able

 * to compute a sample with given data - calling function should check this.

 */

u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)

void tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)

{

	u32 sample = 0,

	u32 sample = 0, delta_v;



	/*

	 * When not to sample:

	 * - on non-data packets

	 *   (RFC 4342, 8.1: CCVal only fully defined for data packets);

	 * - when no data packets have been received yet

	 *   (FIXME: using sampled packet size as indicator here);

	 * - as long as there are gaps in the sequence space (pending loss).

	 */

	if (!dccp_data_packet(skb) || h->packet_size == 0 ||

	    tfrc_rx_hist_loss_pending(h))

		return;



	delta_v = SUB16(dccp_hdr(skb)->dccph_ccval,

			tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
@@ -479,6 +507,6 @@ u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb) 
	h->rtt_sample_prev = 0;	       /* use current entry as next reference */

keep_ref_for_next_time:



	return sample;

	h->rtt_estimate = tfrc_ewma(h->rtt_estimate, sample, 9);

}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_sample_rtt);

net/dccp/ccids/lib/packet_history.h

+15 −2
Original line number Diff line number Diff line
@@ -91,6 +91,7 @@ struct tfrc_rx_hist_entry { 
 * @loss_count:		Number of entries in circular history

 * @loss_start:		Movable index (for loss detection)

 * @rtt_sample_prev:	Used during RTT sampling, points to candidate entry

 * @rtt_estimate:	Receiver RTT estimate

 * @packet_size:	Packet size in bytes (as per RFC 3448, 3.1)

 * @bytes_recvd:	Number of bytes received since last sending feedback

 */
@@ -98,7 +99,10 @@ struct tfrc_rx_hist { 
	struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];

	u8			  loss_count:2,

				  loss_start:2;

	/* Receiver RTT sampling */

#define rtt_sample_prev		  loss_start

	u32			  rtt_estimate;

	/* Receiver sampling of application payload lengths */

	u32			  packet_size,

				  bytes_recvd;

};
@@ -154,6 +158,15 @@ static inline u32 tfrc_rx_hist_packet_size(const struct tfrc_rx_hist *h) 
		return TCP_MIN_RCVMSS;

	}

	return h->packet_size;



}

static inline u32 tfrc_rx_hist_rtt(const struct tfrc_rx_hist *h)

{

	if (h->rtt_estimate == 0) {

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

		return  DCCP_FALLBACK_RTT;

	}

	return h->rtt_estimate;

}



extern void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
@@ -167,7 +180,7 @@ extern int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, 
				struct sk_buff *skb, const u64 ndp,

				u32 (*first_li)(struct sock *sk),

				struct sock *sk);

extern u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h,

extern void tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h,

				    const struct sk_buff *skb);

extern int  tfrc_rx_hist_init(struct tfrc_rx_hist *h, struct sock *sk);

extern void tfrc_rx_hist_purge(struct tfrc_rx_hist *h);