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Commit a79ef76f authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[DCCP] ccid3: Larger initial windows 



This implements the larger-initial-windows feature for CCID 3, as described in
section 5 of RFC 4342. When the first feedback packet arrives, the sender can
send up to 2..4 packets per RTT, instead of just one.

The patch further
 * reduces the number of timestamping calls by passing the timestamp value
   (which is computed in one of the calling functions anyway) as argument

 * renames one constant with a very long name into one which is shorter and
   resembles the one in RFC 3448 (t_mbi)

 * simplifies some of the min_t/max_t cases where both `x', `y' have the same
   type

Commiter note: renamed TFRC_t_mbi to TFRC_T_MBI, to follow Linux coding style.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
parent 841bac1d

net/dccp/ccids/ccid3.c

+35 −31
Original line number Diff line number Diff line
@@ -128,7 +128,8 @@ static inline void ccid3_update_send_time(struct ccid3_hc_tx_sock *hctx) 
 *          X = max(min(2 * X, 2 * X_recv), s / R);

 *          tld = now;

 */ 

static void ccid3_hc_tx_update_x(struct sock *sk)

static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)



{

	struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);

	const __u32 old_x = hctx->ccid3hctx_x;
@@ -138,23 +139,20 @@ static void ccid3_hc_tx_update_x(struct sock *sk) 
		hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s,

						     hctx->ccid3hctx_rtt,

						     hctx->ccid3hctx_p);

		hctx->ccid3hctx_x = max_t(u32, min_t(u32, hctx->ccid3hctx_x_calc,

							  2 * hctx->ccid3hctx_x_recv),

					       (hctx->ccid3hctx_s /

					        TFRC_MAX_BACK_OFF_TIME));

	} else {

		struct timeval now;

		hctx->ccid3hctx_x = max_t(u32, min(hctx->ccid3hctx_x_calc,

						   hctx->ccid3hctx_x_recv * 2),

					       hctx->ccid3hctx_s / TFRC_T_MBI);



		dccp_timestamp(sk, &now);

	       	if (timeval_delta(&now, &hctx->ccid3hctx_t_ld) >=

	} else if (timeval_delta(now, &hctx->ccid3hctx_t_ld) >=

							  hctx->ccid3hctx_rtt) {

			hctx->ccid3hctx_x = max_t(u32, min_t(u32, hctx->ccid3hctx_x_recv,

		hctx->ccid3hctx_x = max(min(hctx->ccid3hctx_x_recv,

					    hctx->ccid3hctx_x      ) * 2,

					usecs_div(hctx->ccid3hctx_s,

					       	  hctx->ccid3hctx_rtt)   );

			hctx->ccid3hctx_t_ld = now;

		}

	}

		hctx->ccid3hctx_t_ld = *now;

	} else

		ccid3_pr_debug("Not changing X\n");



	if (hctx->ccid3hctx_x != old_x)

		ccid3_update_send_time(hctx);

}
@@ -196,12 +194,9 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
	

	switch (hctx->ccid3hctx_state) {

	case TFRC_SSTATE_NO_FBACK:

		/* Halve send rate */

		hctx->ccid3hctx_x /= 2;

		if (hctx->ccid3hctx_x < (hctx->ccid3hctx_s /

					 TFRC_MAX_BACK_OFF_TIME))

			hctx->ccid3hctx_x = (hctx->ccid3hctx_s /

					     TFRC_MAX_BACK_OFF_TIME);

		/* RFC 3448, 4.4: Halve send rate directly */

		hctx->ccid3hctx_x = min_t(u32, hctx->ccid3hctx_x / 2,

					       hctx->ccid3hctx_s / TFRC_T_MBI);



		ccid3_pr_debug("%s, sk=%p, state=%s, updated tx rate to %d "

			       "bytes/s\n",
@@ -221,6 +216,8 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
		if (!hctx->ccid3hctx_idle ||

		    (hctx->ccid3hctx_x_recv >=

		     4 * usecs_div(hctx->ccid3hctx_s, hctx->ccid3hctx_rtt))) {

			struct timeval now;



			ccid3_pr_debug("%s, sk=%p, state=%s, not idle\n",

				       dccp_role(sk), sk,

				       ccid3_tx_state_name(hctx->ccid3hctx_state));
@@ -238,12 +235,13 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
			if (hctx->ccid3hctx_p < TFRC_SMALLEST_P ||

			    hctx->ccid3hctx_x_calc > 2 * hctx->ccid3hctx_x_recv)

				hctx->ccid3hctx_x_recv = max_t(u32, hctx->ccid3hctx_x_recv / 2,

								    hctx->ccid3hctx_s / (2 * TFRC_MAX_BACK_OFF_TIME));

								    hctx->ccid3hctx_s / (2 * TFRC_T_MBI));

			else

				hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc / 4;



			/* Update sending rate */

			ccid3_hc_tx_update_x(sk);

			dccp_timestamp(sk, &now);

			ccid3_hc_tx_update_x(sk, &now);

		}

		/*

		 * Schedule no feedback timer to expire in
@@ -473,11 +471,21 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		 * q is a constant, RFC 3448 recomments 0.9

		 */

		if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {

			ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);

			/* Use Larger Initial Windows [RFC 4342, sec. 5]

			 * We deviate in that we use `s' instead of `MSS'. */

			u16 w_init = max(    4 * hctx->ccid3hctx_s,

					 max(2 * hctx->ccid3hctx_s, 4380));

			hctx->ccid3hctx_rtt  = r_sample;

		} else

			hctx->ccid3hctx_x    = usecs_div(w_init, r_sample);

			hctx->ccid3hctx_t_ld = now;



			ccid3_update_send_time(hctx);

			ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);

		} else {

			hctx->ccid3hctx_rtt = (hctx->ccid3hctx_rtt * 9) / 10 +

					      r_sample / 10;

			ccid3_hc_tx_update_x(sk, &now);

		}



		ccid3_pr_debug("%s, sk=%p, New RTT estimate=%uus, "

			       "r_sample=%us\n", dccp_role(sk), sk,
@@ -502,9 +510,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		/* unschedule no feedback timer */

		sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);



		/* Update sending rate (and likely t_ipi, t_nom, and delta) */

		ccid3_hc_tx_update_x(sk);



		/* remove all packets older than the one acked from history */

		dccp_tx_hist_purge_older(ccid3_tx_hist,

					 &hctx->ccid3hctx_hist, packet);
@@ -514,7 +519,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		 */

		sk->sk_write_space(sk);





		/* Update timeout interval. We use the alternative variant of

		 * [RFC 3448, 3.1] which sets the upper bound of t_rto to one

		 * second, as it is suggested for TCP (see RFC 2988, 2.4). */

net/dccp/ccids/ccid3.h

+2 −2
Original line number Diff line number Diff line
@@ -48,8 +48,8 @@ 
/* In usecs - half the scheduling granularity as per RFC3448 4.6 */

#define TFRC_OPSYS_HALF_TIME_GRAN  (USEC_PER_SEC / (2 * HZ))



/* In seconds */

#define TFRC_MAX_BACK_OFF_TIME	   64

/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */

#define TFRC_T_MBI		   64



#define TFRC_SMALLEST_P		   40