[linux.git] / net / ipv4 / tcp_bic.c

/*
 * Binary Increase Congestion control for TCP
 * Home page:
 *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
 * 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://netsrv.csc.ncsu.edu/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->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)
{
	struct bictcp *ca = inet_csk_ca(sk);

	bictcp_reset(ca);
	ca->loss_cwnd = 0;

	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->last_max_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)
{
	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);
		tcp_cong_avoid_ai(tp, ca->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->loss_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, s32 rtt)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);

	if (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 __read_mostly = {
	.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");
Commit	Line	Data
83803034 SH	1	/*
83803034 SH	2	* Binary Increase Congestion control for TCP
0bc8c7bf SH	3	* Home page:
0bc8c7bf SH	4	* http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
83803034 SH	5	* This is from the implementation of BICTCP in
	6	* Lison-Xu, Kahaled Harfoush, and Injong Rhee.
	7	* "Binary Increase Congestion Control for Fast, Long Distance
	8	* Networks" in InfoComm 2004
	9	* Available from:
0bc8c7bf	10	* http://netsrv.csc.ncsu.edu/export/bitcp.pdf
83803034 SH	11	*
	12	* Unless BIC is enabled and congestion window is large
	13	* this behaves the same as the original Reno.
	14	*/
	15
83803034 SH	16	#include <linux/mm.h>
	17	#include <linux/module.h>
	18	#include <net/tcp.h>
	19
	20
	21	#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
	22	* max_cwnd = snd_cwnd * beta
	23	*/
	24	#define BICTCP_B 4 /*
	25	* In binary search,
	26	* go to point (max+min)/N
	27	*/
	28
	29	static int fast_convergence = 1;
450b5b18	30	static int max_increment = 16;
83803034 SH	31	static int low_window = 14;
83803034 SH	32	static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
66e1e3b2	33	static int initial_ssthresh;
83803034 SH	34	static int smooth_part = 20;
	35
	36	module_param(fast_convergence, int, 0644);
	37	MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
	38	module_param(max_increment, int, 0644);
	39	MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
	40	module_param(low_window, int, 0644);
	41	MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
	42	module_param(beta, int, 0644);
	43	MODULE_PARM_DESC(beta, "beta for multiplicative increase");
83803034 SH	44	module_param(initial_ssthresh, int, 0644);
	45	MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
	46	module_param(smooth_part, int, 0644);
	47	MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
	48
	49
	50	/* BIC TCP Parameters */
	51	struct bictcp {
	52	u32 cnt; /* increase cwnd by 1 after ACKs */
	53	u32 last_max_cwnd; /* last maximum snd_cwnd */
	54	u32 loss_cwnd; /* congestion window at last loss */
	55	u32 last_cwnd; /* the last snd_cwnd */
	56	u32 last_time; /* time when updated last_cwnd */
83803034 SH	57	u32 epoch_start; /* beginning of an epoch */
	58	#define ACK_RATIO_SHIFT 4
	59	u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
	60	};
	61
	62	static inline void bictcp_reset(struct bictcp *ca)
	63	{
	64	ca->cnt = 0;
	65	ca->last_max_cwnd = 0;
83803034 SH	66	ca->last_cwnd = 0;
83803034 SH	67	ca->last_time = 0;
83803034 SH	68	ca->epoch_start = 0;
	69	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
	70	}
	71
6687e988	72	static void bictcp_init(struct sock *sk)
83803034	73	{
fc16dcd8 NC	74	struct bictcp *ca = inet_csk_ca(sk);
	75
	76	bictcp_reset(ca);
	77	ca->loss_cwnd = 0;
	78
83803034	79	if (initial_ssthresh)
6687e988	80	tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
83803034 SH	81	}
	82
	83	/*
	84	* Compute congestion window to use.
	85	*/
	86	static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
	87	{
	88	if (ca->last_cwnd == cwnd &&
	89	(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
	90	return;
	91
	92	ca->last_cwnd = cwnd;
	93	ca->last_time = tcp_time_stamp;
	94
	95	if (ca->epoch_start == 0) /* record the beginning of an epoch */
	96	ca->epoch_start = tcp_time_stamp;
	97
	98	/* start off normal */
	99	if (cwnd <= low_window) {
	100	ca->cnt = cwnd;
	101	return;
	102	}
	103
	104	/* binary increase */
	105	if (cwnd < ca->last_max_cwnd) {
	106	__u32 dist = (ca->last_max_cwnd - cwnd)
	107	/ BICTCP_B;
	108
	109	if (dist > max_increment)
	110	/* linear increase */
	111	ca->cnt = cwnd / max_increment;
	112	else if (dist <= 1U)
	113	/* binary search increase */
	114	ca->cnt = (cwnd * smooth_part) / BICTCP_B;
	115	else
	116	/* binary search increase */
	117	ca->cnt = cwnd / dist;
	118	} else {
	119	/* slow start AMD linear increase */
	120	if (cwnd < ca->last_max_cwnd + BICTCP_B)
	121	/* slow start */
	122	ca->cnt = (cwnd * smooth_part) / BICTCP_B;
	123	else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
	124	/* slow start */
	125	ca->cnt = (cwnd * (BICTCP_B-1))
42a39450	126	/ (cwnd - ca->last_max_cwnd);
83803034 SH	127	else
	128	/* linear increase */
	129	ca->cnt = cwnd / max_increment;
	130	}
	131
	132	/* if in slow start or link utilization is very low */
fc16dcd8	133	if (ca->last_max_cwnd == 0) {
83803034 SH	134	if (ca->cnt > 20) /* increase cwnd 5% per RTT */
	135	ca->cnt = 20;
	136	}
	137
	138	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
	139	if (ca->cnt == 0) /* cannot be zero */
	140	ca->cnt = 1;
	141	}
	142
c3a05c60	143	static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
83803034	144	{
6687e988 ACM	145	struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	146	struct bictcp *ca = inet_csk_ca(sk);
83803034	147
f4805ede	148	if (!tcp_is_cwnd_limited(sk, in_flight))
83803034 SH	149	return;
83803034 SH	150
7faffa1c SH	151	if (tp->snd_cwnd <= tp->snd_ssthresh)
	152	tcp_slow_start(tp);
	153	else {
83803034	154	bictcp_update(ca, tp->snd_cwnd);
758ce5c8	155	tcp_cong_avoid_ai(tp, ca->cnt);
83803034 SH	156	}
	157
	158	}
	159
	160	/*
	161	* behave like Reno until low_window is reached,
	162	* then increase congestion window slowly
	163	*/
6687e988	164	static u32 bictcp_recalc_ssthresh(struct sock *sk)
83803034	165	{
6687e988 ACM	166	const struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	167	struct bictcp *ca = inet_csk_ca(sk);
83803034 SH	168
	169	ca->epoch_start = 0; /* end of epoch */
	170
83803034 SH	171	/* Wmax and fast convergence */
	172	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
	173	ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
	174	/ (2 * BICTCP_BETA_SCALE);
	175	else
	176	ca->last_max_cwnd = tp->snd_cwnd;
	177
	178	ca->loss_cwnd = tp->snd_cwnd;
	179
	180
	181	if (tp->snd_cwnd <= low_window)
	182	return max(tp->snd_cwnd >> 1U, 2U);
	183	else
	184	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
	185	}
	186
6687e988	187	static u32 bictcp_undo_cwnd(struct sock *sk)
83803034	188	{
6687e988 ACM	189	const struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	190	const struct bictcp *ca = inet_csk_ca(sk);
fc16dcd8	191	return max(tp->snd_cwnd, ca->loss_cwnd);
83803034 SH	192	}
83803034 SH	193
6687e988	194	static void bictcp_state(struct sock *sk, u8 new_state)
83803034 SH	195	{
83803034 SH	196	if (new_state == TCP_CA_Loss)
6687e988	197	bictcp_reset(inet_csk_ca(sk));
83803034 SH	198	}
83803034 SH	199
05d05450	200	/* Track delayed acknowledgment ratio using sliding window
83803034 SH	201	* ratio = (15*ratio + sample) / 16
83803034 SH	202	*/
30cfd0ba	203	static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
83803034	204	{
6687e988 ACM	205	const struct inet_connection_sock *icsk = inet_csk(sk);
6687e988 ACM	206
35e86941	207	if (icsk->icsk_ca_state == TCP_CA_Open) {
6687e988	208	struct bictcp *ca = inet_csk_ca(sk);
83803034 SH	209	cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
	210	ca->delayed_ack += cnt;
	211	}
	212	}
	213
	214
a252bebe	215	static struct tcp_congestion_ops bictcp __read_mostly = {
83803034 SH	216	.init = bictcp_init,
	217	.ssthresh = bictcp_recalc_ssthresh,
	218	.cong_avoid = bictcp_cong_avoid,
	219	.set_state = bictcp_state,
	220	.undo_cwnd = bictcp_undo_cwnd,
83803034 SH	221	.pkts_acked = bictcp_acked,
	222	.owner = THIS_MODULE,
	223	.name = "bic",
	224	};
	225
	226	static int __init bictcp_register(void)
	227	{
65e3d726	228	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
83803034 SH	229	return tcp_register_congestion_control(&bictcp);
	230	}
	231
	232	static void __exit bictcp_unregister(void)
	233	{
	234	tcp_unregister_congestion_control(&bictcp);
	235	}
	236
	237	module_init(bictcp_register);
	238	module_exit(bictcp_unregister);
	239
	240	MODULE_AUTHOR("Stephen Hemminger");
	241	MODULE_LICENSE("GPL");
	242	MODULE_DESCRIPTION("BIC TCP");