net/ipv4/tcp_bic.c - linux - Git at Google

 /*
  * Binary Increase Congestion control for TCP
  *
  * This is from the implementation of BICTCP in
  * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
  *  "Binary Increase Congestion Control for Fast, Long Distance
  *  Networks" in InfoComm 2004
  * Available from:
  *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
  *
  * Unless BIC is enabled and congestion window is large
  * this behaves the same as the original Reno.
  */

 #include <linux/mm.h>
 #include <linux/module.h>
 #include <net/tcp.h>


 #define BICTCP_BETA_SCALE    1024	/* Scale factor beta calculation
 					 * max_cwnd = snd_cwnd * beta
 					 */
 #define BICTCP_B		4	 /*
 					  * In binary search,
 					  * go to point (max+min)/N
 					  */

 static int fast_convergence = 1;
 static int max_increment = 16;
 static int low_window = 14;
 static int beta = 819;		/* = 819/1024 (BICTCP_BETA_SCALE) */
 static int initial_ssthresh;
 static int smooth_part = 20;

 module_param(fast_convergence, int, 0644);
 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
 module_param(max_increment, int, 0644);
 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
 module_param(low_window, int, 0644);
 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
 module_param(beta, int, 0644);
 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
 module_param(initial_ssthresh, int, 0644);
 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
 module_param(smooth_part, int, 0644);
 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");


 /* BIC TCP Parameters */
 struct bictcp {
 	u32	cnt;		/* increase cwnd by 1 after ACKs */
 	u32 	last_max_cwnd;	/* last maximum snd_cwnd */
 	u32	loss_cwnd;	/* congestion window at last loss */
 	u32	last_cwnd;	/* the last snd_cwnd */
 	u32	last_time;	/* time when updated last_cwnd */
 	u32	epoch_start;	/* beginning of an epoch */
 #define ACK_RATIO_SHIFT	4
 	u32	delayed_ack;	/* estimate the ratio of Packets/ACKs << 4 */
 };

 static inline void bictcp_reset(struct bictcp *ca)
 {
 	ca->cnt = 0;
 	ca->last_max_cwnd = 0;
 	ca->loss_cwnd = 0;
 	ca->last_cwnd = 0;
 	ca->last_time = 0;
 	ca->epoch_start = 0;
 	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
 }

 static void bictcp_init(struct sock *sk)
 {
 	bictcp_reset(inet_csk_ca(sk));
 	if (initial_ssthresh)
 		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
 }

 /*
  * Compute congestion window to use.
  */
 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 {
 	if (ca->last_cwnd == cwnd &&
 	    (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
 		return;

 	ca->last_cwnd = cwnd;
 	ca->last_time = tcp_time_stamp;

 	if (ca->epoch_start == 0) /* record the beginning of an epoch */
 		ca->epoch_start = tcp_time_stamp;

 	/* start off normal */
 	if (cwnd <= low_window) {
 		ca->cnt = cwnd;
 		return;
 	}

 	/* binary increase */
 	if (cwnd < ca->last_max_cwnd) {
 		__u32 	dist = (ca->last_max_cwnd - cwnd)
 			/ BICTCP_B;

 		if (dist > max_increment)
 			/* linear increase */
 			ca->cnt = cwnd / max_increment;
 		else if (dist <= 1U)
 			/* binary search increase */
 			ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 		else
 			/* binary search increase */
 			ca->cnt = cwnd / dist;
 	} else {
 		/* slow start AMD linear increase */
 		if (cwnd < ca->last_max_cwnd + BICTCP_B)
 			/* slow start */
 			ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 		else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 			/* slow start */
 			ca->cnt = (cwnd * (BICTCP_B-1))
 				/ (cwnd - ca->last_max_cwnd);
 		else
 			/* linear increase */
 			ca->cnt = cwnd / max_increment;
 	}

 	/* if in slow start or link utilization is very low */
 	if (ca->loss_cwnd == 0) {
 		if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 			ca->cnt = 20;
 	}

 	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 	if (ca->cnt == 0)			/* cannot be zero */
 		ca->cnt = 1;
 }

 static void bictcp_cong_avoid(struct sock *sk, u32 ack,
 			      u32 in_flight, int data_acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);

 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;

 	if (tp->snd_cwnd <= tp->snd_ssthresh)
 		tcp_slow_start(tp);
 	else {
 		bictcp_update(ca, tp->snd_cwnd);

 		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 		 */
 		if (tp->snd_cwnd_cnt >= ca->cnt) {
 			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 				tp->snd_cwnd++;
 			tp->snd_cwnd_cnt = 0;
 		} else
 			tp->snd_cwnd_cnt++;
 	}

 }

 /*
  *	behave like Reno until low_window is reached,
  *	then increase congestion window slowly
  */
 static u32 bictcp_recalc_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);

 	ca->epoch_start = 0;	/* end of epoch */

 	/* Wmax and fast convergence */
 	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 		ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 			/ (2 * BICTCP_BETA_SCALE);
 	else
 		ca->last_max_cwnd = tp->snd_cwnd;

 	ca->loss_cwnd = tp->snd_cwnd;


 	if (tp->snd_cwnd <= low_window)
 		return max(tp->snd_cwnd >> 1U, 2U);
 	else
 		return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 }

 static u32 bictcp_undo_cwnd(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct bictcp *ca = inet_csk_ca(sk);
 	return max(tp->snd_cwnd, ca->last_max_cwnd);
 }

 static void bictcp_state(struct sock *sk, u8 new_state)
 {
 	if (new_state == TCP_CA_Loss)
 		bictcp_reset(inet_csk_ca(sk));
 }

 /* Track delayed acknowledgment ratio using sliding window
  * ratio = (15*ratio + sample) / 16
  */
 static void bictcp_acked(struct sock *sk, u32 cnt, ktime_t last)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);

 	if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
 		struct bictcp *ca = inet_csk_ca(sk);
 		cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 		ca->delayed_ack += cnt;
 	}
 }


 static struct tcp_congestion_ops bictcp = {
 	.init		= bictcp_init,
 	.ssthresh	= bictcp_recalc_ssthresh,
 	.cong_avoid	= bictcp_cong_avoid,
 	.set_state	= bictcp_state,
 	.undo_cwnd	= bictcp_undo_cwnd,
 	.pkts_acked     = bictcp_acked,
 	.owner		= THIS_MODULE,
 	.name		= "bic",
 };

 static int __init bictcp_register(void)
 {
 	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 	return tcp_register_congestion_control(&bictcp);
 }

 static void __exit bictcp_unregister(void)
 {
 	tcp_unregister_congestion_control(&bictcp);
 }

 module_init(bictcp_register);
 module_exit(bictcp_unregister);

 MODULE_AUTHOR("Stephen Hemminger");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("BIC TCP");
	/*
	* Binary Increase Congestion control for TCP
	*
	* This is from the implementation of BICTCP in
	* Lison-Xu, Kahaled Harfoush, and Injong Rhee.
	* "Binary Increase Congestion Control for Fast, Long Distance
	* Networks" in InfoComm 2004
	* Available from:
	* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
	*
	* Unless BIC is enabled and congestion window is large
	* this behaves the same as the original Reno.
	*/

	#include <linux/mm.h>
	#include <linux/module.h>
	#include <net/tcp.h>


	#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
	* max_cwnd = snd_cwnd * beta
	*/
	#define BICTCP_B 4 /*
	* In binary search,
	* go to point (max+min)/N
	*/

	static int fast_convergence = 1;
	static int max_increment = 16;
	static int low_window = 14;
	static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
	static int initial_ssthresh;
	static int smooth_part = 20;

	module_param(fast_convergence, int, 0644);
	MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
	module_param(max_increment, int, 0644);
	MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
	module_param(low_window, int, 0644);
	MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
	module_param(beta, int, 0644);
	MODULE_PARM_DESC(beta, "beta for multiplicative increase");
	module_param(initial_ssthresh, int, 0644);
	MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
	module_param(smooth_part, int, 0644);
	MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");


	/* BIC TCP Parameters */
	struct bictcp {
	u32 cnt; /* increase cwnd by 1 after ACKs */
	u32 last_max_cwnd; /* last maximum snd_cwnd */
	u32 loss_cwnd; /* congestion window at last loss */
	u32 last_cwnd; /* the last snd_cwnd */
	u32 last_time; /* time when updated last_cwnd */
	u32 epoch_start; /* beginning of an epoch */
	#define ACK_RATIO_SHIFT 4
	u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
	};

	static inline void bictcp_reset(struct bictcp *ca)
	{
	ca->cnt = 0;
	ca->last_max_cwnd = 0;
	ca->loss_cwnd = 0;
	ca->last_cwnd = 0;
	ca->last_time = 0;
	ca->epoch_start = 0;
	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
	}

	static void bictcp_init(struct sock *sk)
	{
	bictcp_reset(inet_csk_ca(sk));
	if (initial_ssthresh)
	tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
	}

	/*
	* Compute congestion window to use.
	*/
	static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
	{
	if (ca->last_cwnd == cwnd &&
	(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
	return;

	ca->last_cwnd = cwnd;
	ca->last_time = tcp_time_stamp;

	if (ca->epoch_start == 0) /* record the beginning of an epoch */
	ca->epoch_start = tcp_time_stamp;

	/* start off normal */
	if (cwnd <= low_window) {
	ca->cnt = cwnd;
	return;
	}

	/* binary increase */
	if (cwnd < ca->last_max_cwnd) {
	__u32 dist = (ca->last_max_cwnd - cwnd)
	/ BICTCP_B;

	if (dist > max_increment)
	/* linear increase */
	ca->cnt = cwnd / max_increment;
	else if (dist <= 1U)
	/* binary search increase */
	ca->cnt = (cwnd * smooth_part) / BICTCP_B;
	else
	/* binary search increase */
	ca->cnt = cwnd / dist;
	} else {
	/* slow start AMD linear increase */
	if (cwnd < ca->last_max_cwnd + BICTCP_B)
	/* slow start */
	ca->cnt = (cwnd * smooth_part) / BICTCP_B;
	else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
	/* slow start */
	ca->cnt = (cwnd * (BICTCP_B-1))
	/ (cwnd - ca->last_max_cwnd);
	else
	/* linear increase */
	ca->cnt = cwnd / max_increment;
	}

	/* if in slow start or link utilization is very low */
	if (ca->loss_cwnd == 0) {
	if (ca->cnt > 20) /* increase cwnd 5% per RTT */
	ca->cnt = 20;
	}

	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
	if (ca->cnt == 0) /* cannot be zero */
	ca->cnt = 1;
	}

	static void bictcp_cong_avoid(struct sock *sk, u32 ack,
	u32 in_flight, int data_acked)
	{
	struct tcp_sock *tp = tcp_sk(sk);
	struct bictcp *ca = inet_csk_ca(sk);

	if (!tcp_is_cwnd_limited(sk, in_flight))
	return;

	if (tp->snd_cwnd <= tp->snd_ssthresh)
	tcp_slow_start(tp);
	else {
	bictcp_update(ca, tp->snd_cwnd);

	/* In dangerous area, increase slowly.
	* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
	*/
	if (tp->snd_cwnd_cnt >= ca->cnt) {
	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	tp->snd_cwnd++;
	tp->snd_cwnd_cnt = 0;
	} else
	tp->snd_cwnd_cnt++;
	}

	}

	/*
	* behave like Reno until low_window is reached,
	* then increase congestion window slowly
	*/
	static u32 bictcp_recalc_ssthresh(struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct bictcp *ca = inet_csk_ca(sk);

	ca->epoch_start = 0; /* end of epoch */

	/* Wmax and fast convergence */
	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
	ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
	/ (2 * BICTCP_BETA_SCALE);
	else
	ca->last_max_cwnd = tp->snd_cwnd;

	ca->loss_cwnd = tp->snd_cwnd;


	if (tp->snd_cwnd <= low_window)
	return max(tp->snd_cwnd >> 1U, 2U);
	else
	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
	}

	static u32 bictcp_undo_cwnd(struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct bictcp *ca = inet_csk_ca(sk);
	return max(tp->snd_cwnd, ca->last_max_cwnd);
	}

	static void bictcp_state(struct sock *sk, u8 new_state)
	{
	if (new_state == TCP_CA_Loss)
	bictcp_reset(inet_csk_ca(sk));
	}

	/* Track delayed acknowledgment ratio using sliding window
	* ratio = (15*ratio + sample) / 16
	*/
	static void bictcp_acked(struct sock *sk, u32 cnt, ktime_t last)
	{
	const struct inet_connection_sock *icsk = inet_csk(sk);

	if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
	struct bictcp *ca = inet_csk_ca(sk);
	cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
	ca->delayed_ack += cnt;
	}
	}


	static struct tcp_congestion_ops bictcp = {
	.init = bictcp_init,
	.ssthresh = bictcp_recalc_ssthresh,
	.cong_avoid = bictcp_cong_avoid,
	.set_state = bictcp_state,
	.undo_cwnd = bictcp_undo_cwnd,
	.pkts_acked = bictcp_acked,
	.owner = THIS_MODULE,
	.name = "bic",
	};

	static int __init bictcp_register(void)
	{
	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
	return tcp_register_congestion_control(&bictcp);
	}

	static void __exit bictcp_unregister(void)
	{
	tcp_unregister_congestion_control(&bictcp);
	}

	module_init(bictcp_register);
	module_exit(bictcp_unregister);

	MODULE_AUTHOR("Stephen Hemminger");
	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("BIC TCP");