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Commit 34a081be authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp tfrc: Let dccp_tfrc_lib do the sampling work 



This migrates more TFRC-related code into the dccp_tfrc_lib:
 * sampling of the packet size `s' (which is only needed until the first
   loss interval is computed (ccid3_first_li));
 * updating the byte-counter `bytes_recvd' in between sending feedbacks.
The result is a better separation of CCID-3 specific and TFRC specific
code, which aids future integration with ECN and e.g. CCID-4.

Further changes:
----------------
 * replaced magic number of 536 with equivalent constant TCP_MIN_RCVMSS;
   (this constant is also used when no estimate for `s' is available).

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 3ca7aea0

net/dccp/ccids/ccid3.c

+8 −30
Original line number Diff line number Diff line
@@ -590,12 +590,9 @@ 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 = hcrx->s;

			u32 rtt = hcrx->rtt ? : DCCP_FALLBACK_RTT,

			    s	= tfrc_rx_hist_packet_size(&hcrx->hist);



			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;

		}
@@ -617,7 +614,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk, 
		if (delta <= 0)

			DCCP_BUG("delta (%ld) <= 0", (long)delta);

		else

			hcrx->x_recv = scaled_div32(hcrx->bytes_recv, delta);

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

		break;

	default:

		return;
@@ -628,7 +625,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk, 


	hcrx->tstamp_last_feedback = now;

	hcrx->last_counter	   = dccp_hdr(skb)->dccph_ccval;

	hcrx->bytes_recv	   = 0;

	hcrx->hist.bytes_recvd	   = 0;



	dp->dccps_hc_rx_insert_options = 1;

	dccp_send_ack(sk);
@@ -669,7 +666,8 @@ 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;

	u32 x_recv, p, delta,

	    s = tfrc_rx_hist_packet_size(&hcrx->hist);

	u64 fval;



	/*
@@ -686,7 +684,7 @@ static u32 ccid3_first_li(struct sock *sk) 
	}



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

	x_recv = scaled_div32(hcrx->bytes_recv, delta);

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

	if (x_recv == 0) {		/* would also trigger divide-by-zero */

		DCCP_WARN("X_recv==0\n");

		if (hcrx->x_recv == 0) {
@@ -696,8 +694,7 @@ static u32 ccid3_first_li(struct sock *sk) 
		x_recv = hcrx->x_recv;

	}



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

	fval = scaled_div32(fval, x_recv);

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

	p = tfrc_calc_x_reverse_lookup(fval);



	ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
@@ -724,31 +721,12 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb) 


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

		if (is_data_packet) {

			const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;

			do_feedback = CCID3_FBACK_INITIAL;

			ccid3_hc_rx_set_state(sk, TFRC_RSTATE_DATA);

			hcrx->s = payload;

			/*

			 * Not necessary to update bytes_recv here,

			 * since X_recv = 0 for the first feedback packet (cf.

			 * RFC 3448, 6.3) -- gerrit

			 */

		}

		goto update_records;

	}



	if (tfrc_rx_hist_duplicate(&hcrx->hist, skb))

		return; /* done receiving */



	if (is_data_packet) {

		const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;

		/*

		 * Update moving-average of s and the sum of received payload bytes

		 */

		hcrx->s = tfrc_ewma(hcrx->s, payload, 9);

		hcrx->bytes_recv += payload;

	}



	if (tfrc_rx_hist_loss_pending(&hcrx->hist))

		return; /* done receiving */

net/dccp/ccids/ccid3.h

+0 −4
Original line number Diff line number Diff line
@@ -124,25 +124,21 @@ enum ccid3_hc_rx_states { 
 *

 *  @last_counter  -  Tracks window counter (RFC 4342, 8.1)

 *  @state  -  Receiver state, one of %ccid3_hc_rx_states

 *  @bytes_recv  -  Total sum of DCCP payload bytes

 *  @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

 *  @s  -  Received packet size in bytes

 *  @p_inverse  -  Inverse of Loss Event Rate (RFC 4342, sec. 8.5)

 */

struct ccid3_hc_rx_sock {

	u8				last_counter:4;

	enum ccid3_hc_rx_states		state:8;

	u32				bytes_recv;

	u32				x_recv;

	u32				rtt;

	ktime_t				tstamp_last_feedback;

	struct tfrc_rx_hist		hist;

	struct tfrc_loss_hist		li_hist;

	u16				s;

#define p_inverse			li_hist.i_mean

};

net/dccp/ccids/lib/packet_history.c

+10 −0
Original line number Diff line number Diff line
@@ -352,6 +352,16 @@ int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, 
		__three_after_loss(h);

	}



	/*

	 * Update moving-average of `s' and the sum of received payload bytes.

	 */

	if (dccp_data_packet(skb)) {

		const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;



		h->packet_size = tfrc_ewma(h->packet_size, payload, 9);

		h->bytes_recvd += payload;

	}



	/* RFC 3448, 6.1: update I_0, whose growth implies p <= p_prev */

	if (!is_new_loss)

		tfrc_lh_update_i_mean(lh, skb);

net/dccp/ccids/lib/packet_history.h

+16 −0
Original line number Diff line number Diff line
@@ -91,12 +91,16 @@ 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

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

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

 */

struct tfrc_rx_hist {

	struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];

	u8			  loss_count:2,

				  loss_start:2;

#define rtt_sample_prev		  loss_start

	u32			  packet_size,

				  bytes_recvd;

};



/**
@@ -140,6 +144,18 @@ static inline bool tfrc_rx_hist_loss_pending(const struct tfrc_rx_hist *h) 
	return h->loss_count > 0;

}



/*

 * Accessor functions to retrieve parameters sampled by the RX history

 */

static inline u32 tfrc_rx_hist_packet_size(const struct tfrc_rx_hist *h)

{

	if (h->packet_size == 0) {

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

		return TCP_MIN_RCVMSS;

	}

	return h->packet_size;

}



extern void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,

				    const struct sk_buff *skb, const u64 ndp);

net/dccp/proto.c

+1 −1
Original line number Diff line number Diff line
@@ -185,7 +185,7 @@ int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized) 
	sk->sk_state		= DCCP_CLOSED;

	sk->sk_write_space	= dccp_write_space;

	icsk->icsk_sync_mss	= dccp_sync_mss;

	dp->dccps_mss_cache	= 536;

	dp->dccps_mss_cache	= TCP_MIN_RCVMSS;

	dp->dccps_rate_last	= jiffies;

	dp->dccps_role		= DCCP_ROLE_UNDEFINED;

	dp->dccps_service	= DCCP_SERVICE_CODE_IS_ABSENT;