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

/*
 * TCP CUBIC: Binary Increase Congestion control for TCP v2.0
 *
 * This is from the implementation of CUBIC TCP in
 * Injong Rhee, Lisong Xu.
 *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant
 *  in PFLDnet 2005
 * Available from:
 *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
 *
 * Unless CUBIC 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>
#include <asm/div64.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
					  */
#define	BICTCP_HZ		10	/* BIC HZ 2^10 = 1024 */

static int fast_convergence __read_mostly = 1;
static int max_increment __read_mostly = 16;
static int beta __read_mostly = 819;	/* = 819/1024 (BICTCP_BETA_SCALE) */
static int initial_ssthresh __read_mostly = 100;
static int bic_scale __read_mostly = 41;
static int tcp_friendliness __read_mostly = 1;

static u32 cube_rtt_scale __read_mostly;
static u32 beta_scale __read_mostly;
static u64 cube_factor __read_mostly;

/* Note parameters that are used for precomputing scale factors are read-only */
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(beta, int, 0444);
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(bic_scale, int, 0444);
MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
module_param(tcp_friendliness, int, 0644);
MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");

#include <asm/div64.h>

/* 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	bic_origin_point;/* origin point of bic function */
	u32	bic_K;		/* time to origin point from the beginning of the current epoch */
	u32	delay_min;	/* min delay */
	u32	epoch_start;	/* beginning of an epoch */
	u32	ack_cnt;	/* number of acks */
	u32	tcp_cwnd;	/* estimated tcp cwnd */
#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->bic_origin_point = 0;
	ca->bic_K = 0;
	ca->delay_min = 0;
	ca->epoch_start = 0;
	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
	ca->ack_cnt = 0;
	ca->tcp_cwnd = 0;
}

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

/* 64bit divisor, dividend and result. dynamic precision */
static inline u_int64_t div64_64(u_int64_t dividend, u_int64_t divisor)
{
	u_int32_t d = divisor;

	if (divisor > 0xffffffffULL) {
		unsigned int shift = fls(divisor >> 32);

		d = divisor >> shift;
		dividend >>= shift;
	}

	/* avoid 64 bit division if possible */
	if (dividend >> 32)
		do_div(dividend, d);
	else
		dividend = (uint32_t) dividend / d;

	return dividend;
}

/*
 * calculate the cubic root of x using Newton-Raphson
 */
static u32 cubic_root(u64 a)
{
	u32 x, x1;

	/* Initial estimate is based on:
	 * cbrt(x) = exp(log(x) / 3)
	 */
	x = 1u << (fls64(a)/3);

	/*
	 * Iteration based on:
	 *                         2
	 * x    = ( 2 * x  +  a / x  ) / 3
	 *  k+1          k         k
	 */
	do {
		x1 = x;
		x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3;
	} while (abs(x1 - x) > 1);

	return x;
}

/*
 * Compute congestion window to use.
 */
static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
{
	u64 offs;
	u32 delta, t, bic_target, min_cnt, max_cnt;

	ca->ack_cnt++;	/* count the number of ACKs */

	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) {
		ca->epoch_start = tcp_time_stamp;	/* record the beginning of an epoch */
		ca->ack_cnt = 1;			/* start counting */
		ca->tcp_cwnd = cwnd;			/* syn with cubic */

		if (ca->last_max_cwnd <= cwnd) {
			ca->bic_K = 0;
			ca->bic_origin_point = cwnd;
		} else {
			/* Compute new K based on
			 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
			 */
			ca->bic_K = cubic_root(cube_factor
					       * (ca->last_max_cwnd - cwnd));
			ca->bic_origin_point = ca->last_max_cwnd;
		}
	}

	/* cubic function - calc*/
	/* calculate c * time^3 / rtt,
	 *  while considering overflow in calculation of time^3
	 * (so time^3 is done by using 64 bit)
	 * and without the support of division of 64bit numbers
	 * (so all divisions are done by using 32 bit)
	 *  also NOTE the unit of those veriables
	 *	  time  = (t - K) / 2^bictcp_HZ
	 *	  c = bic_scale >> 10
	 * rtt  = (srtt >> 3) / HZ
	 * !!! The following code does not have overflow problems,
	 * if the cwnd < 1 million packets !!!
	 */

	/* change the unit from HZ to bictcp_HZ */
	t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
	     << BICTCP_HZ) / HZ;

	if (t < ca->bic_K)		/* t - K */
		offs = ca->bic_K - t;
	else
		offs = t - ca->bic_K;

	/* c/rtt * (t-K)^3 */
	delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
	if (t < ca->bic_K)                                	/* below origin*/
		bic_target = ca->bic_origin_point - delta;
	else                                                	/* above origin*/
		bic_target = ca->bic_origin_point + delta;

	/* cubic function - calc bictcp_cnt*/
	if (bic_target > cwnd) {
		ca->cnt = cwnd / (bic_target - cwnd);
	} else {
		ca->cnt = 100 * cwnd;              /* very small increment*/
	}

	if (ca->delay_min > 0) {
		/* max increment = Smax * rtt / 0.1  */
		min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
		if (ca->cnt < min_cnt)
			ca->cnt = min_cnt;
	}

	/* slow start and low utilization  */
	if (ca->loss_cwnd == 0)		/* could be aggressive in slow start */
		ca->cnt = 50;

	/* TCP Friendly */
	if (tcp_friendliness) {
		u32 scale = beta_scale;
		delta = (cwnd * scale) >> 3;
		while (ca->ack_cnt > delta) {		/* update tcp cwnd */
			ca->ack_cnt -= delta;
			ca->tcp_cwnd++;
		}

		if (ca->tcp_cwnd > cwnd){	/* if bic is slower than tcp */
			delta = ca->tcp_cwnd - cwnd;
			max_cnt = cwnd / delta;
			if (ca->cnt > max_cnt)
				ca->cnt = max_cnt;
		}
	}

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


/* Keep track of minimum rtt */
static inline void measure_delay(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct bictcp *ca = inet_csk_ca(sk);
	u32 delay;

	/* No time stamp */
	if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
	     /* Discard delay samples right after fast recovery */
	    (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
		return;

	delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3;
	if (delay == 0)
		delay = 1;

	/* first time call or link delay decreases */
	if (ca->delay_min == 0 || ca->delay_min > delay)
		ca->delay_min = delay;
}

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

	if (data_acked)
		measure_delay(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++;
	}

}

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;

	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
}

static u32 bictcp_undo_cwnd(struct sock *sk)
{
	struct bictcp *ca = inet_csk_ca(sk);

	return max(tcp_sk(sk)->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)
{
	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 cubictcp = {
	.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		= "cubic",
};

static int __init cubictcp_register(void)
{
	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);

	/* Precompute a bunch of the scaling factors that are used per-packet
	 * based on SRTT of 100ms
	 */

	beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);

	cube_rtt_scale = (bic_scale * 10);	/* 1024*c/rtt */

	/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
	 *  so K = cubic_root( (wmax-cwnd)*rtt/c )
	 * the unit of K is bictcp_HZ=2^10, not HZ
	 *
	 *  c = bic_scale >> 10
	 *  rtt = 100ms
	 *
	 * the following code has been designed and tested for
	 * cwnd < 1 million packets
	 * RTT < 100 seconds
	 * HZ < 1,000,00  (corresponding to 10 nano-second)
	 */

	/* 1/c * 2^2*bictcp_HZ * srtt */
	cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */

	/* divide by bic_scale and by constant Srtt (100ms) */
	do_div(cube_factor, bic_scale * 10);

	return tcp_register_congestion_control(&cubictcp);
}

static void __exit cubictcp_unregister(void)
{
	tcp_unregister_congestion_control(&cubictcp);
}

module_init(cubictcp_register);
module_exit(cubictcp_unregister);

MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CUBIC TCP");
MODULE_VERSION("2.0");
Commit	Line	Data
df3271f3 SH	1	/*
	2	* TCP CUBIC: Binary Increase Congestion control for TCP v2.0
	3	*
	4	* This is from the implementation of CUBIC TCP in
	5	* Injong Rhee, Lisong Xu.
	6	* "CUBIC: A New TCP-Friendly High-Speed TCP Variant
	7	* in PFLDnet 2005
	8	* Available from:
	9	* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
	10	*
	11	* Unless CUBIC is enabled and congestion window is large
	12	* this behaves the same as the original Reno.
	13	*/
	14
df3271f3 SH	15	#include <linux/mm.h>
	16	#include <linux/module.h>
	17	#include <net/tcp.h>
89b3d9aa	18	#include <asm/div64.h>
df3271f3 SH	19
	20	#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
	21	* max_cwnd = snd_cwnd * beta
	22	*/
	23	#define BICTCP_B 4 /*
	24	* In binary search,
	25	* go to point (max+min)/N
	26	*/
	27	#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
	28
59758f44 SH	29	static int fast_convergence __read_mostly = 1;
	30	static int max_increment __read_mostly = 16;
	31	static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
	32	static int initial_ssthresh __read_mostly = 100;
	33	static int bic_scale __read_mostly = 41;
	34	static int tcp_friendliness __read_mostly = 1;
df3271f3	35
59758f44 SH	36	static u32 cube_rtt_scale __read_mostly;
	37	static u32 beta_scale __read_mostly;
	38	static u64 cube_factor __read_mostly;
89b3d9aa SH	39
89b3d9aa SH	40	/* Note parameters that are used for precomputing scale factors are read-only */
df3271f3 SH	41	module_param(fast_convergence, int, 0644);
	42	MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
	43	module_param(max_increment, int, 0644);
	44	MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
89b3d9aa	45	module_param(beta, int, 0444);
df3271f3 SH	46	MODULE_PARM_DESC(beta, "beta for multiplicative increase");
	47	module_param(initial_ssthresh, int, 0644);
	48	MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
89b3d9aa	49	module_param(bic_scale, int, 0444);
df3271f3 SH	50	MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
	51	module_param(tcp_friendliness, int, 0644);
	52	MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
	53
9eb2d627	54	#include <asm/div64.h>
df3271f3 SH	55
	56	/* BIC TCP Parameters */
	57	struct bictcp {
	58	u32 cnt; /* increase cwnd by 1 after ACKs */
	59	u32 last_max_cwnd; /* last maximum snd_cwnd */
	60	u32 loss_cwnd; /* congestion window at last loss */
	61	u32 last_cwnd; /* the last snd_cwnd */
	62	u32 last_time; /* time when updated last_cwnd */
	63	u32 bic_origin_point;/* origin point of bic function */
	64	u32 bic_K; /* time to origin point from the beginning of the current epoch */
	65	u32 delay_min; /* min delay */
	66	u32 epoch_start; /* beginning of an epoch */
	67	u32 ack_cnt; /* number of acks */
	68	u32 tcp_cwnd; /* estimated tcp cwnd */
	69	#define ACK_RATIO_SHIFT 4
	70	u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
	71	};
	72
	73	static inline void bictcp_reset(struct bictcp *ca)
	74	{
	75	ca->cnt = 0;
	76	ca->last_max_cwnd = 0;
	77	ca->loss_cwnd = 0;
	78	ca->last_cwnd = 0;
	79	ca->last_time = 0;
	80	ca->bic_origin_point = 0;
	81	ca->bic_K = 0;
	82	ca->delay_min = 0;
	83	ca->epoch_start = 0;
	84	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
	85	ca->ack_cnt = 0;
	86	ca->tcp_cwnd = 0;
	87	}
	88
	89	static void bictcp_init(struct sock *sk)
	90	{
	91	bictcp_reset(inet_csk_ca(sk));
	92	if (initial_ssthresh)
	93	tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
	94	}
	95
9eb2d627 SH	96	/* 64bit divisor, dividend and result. dynamic precision */
	97	static inline u_int64_t div64_64(u_int64_t dividend, u_int64_t divisor)
	98	{
	99	u_int32_t d = divisor;
	100
	101	if (divisor > 0xffffffffULL) {
	102	unsigned int shift = fls(divisor >> 32);
	103
	104	d = divisor >> shift;
	105	dividend >>= shift;
	106	}
	107
	108	/* avoid 64 bit division if possible */
	109	if (dividend >> 32)
	110	do_div(dividend, d);
	111	else
	112	dividend = (uint32_t) dividend / d;
	113
	114	return dividend;
	115	}
df3271f3 SH	116
df3271f3 SH	117	/*
9eb2d627	118	* calculate the cubic root of x using Newton-Raphson
df3271f3	119	*/
9eb2d627	120	static u32 cubic_root(u64 a)
df3271f3	121	{
9eb2d627 SH	122	u32 x, x1;
	123
	124	/* Initial estimate is based on:
	125	* cbrt(x) = exp(log(x) / 3)
	126	*/
	127	x = 1u << (fls64(a)/3);
	128
	129	/*
	130	* Iteration based on:
	131	* 2
	132	* x = ( 2 * x + a / x ) / 3
	133	* k+1 k k
	134	*/
	135	do {
	136	x1 = x;
	137	x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3;
	138	} while (abs(x1 - x) > 1);
	139
	140	return x;
df3271f3 SH	141	}
df3271f3 SH	142
df3271f3 SH	143	/*
	144	* Compute congestion window to use.
	145	*/
	146	static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
	147	{
89b3d9aa SH	148	u64 offs;
89b3d9aa SH	149	u32 delta, t, bic_target, min_cnt, max_cnt;
df3271f3 SH	150
	151	ca->ack_cnt++; /* count the number of ACKs */
	152
	153	if (ca->last_cwnd == cwnd &&
	154	(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
	155	return;
	156
	157	ca->last_cwnd = cwnd;
	158	ca->last_time = tcp_time_stamp;
	159
df3271f3 SH	160	if (ca->epoch_start == 0) {
	161	ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
	162	ca->ack_cnt = 1; /* start counting */
	163	ca->tcp_cwnd = cwnd; /* syn with cubic */
	164
	165	if (ca->last_max_cwnd <= cwnd) {
	166	ca->bic_K = 0;
	167	ca->bic_origin_point = cwnd;
	168	} else {
89b3d9aa SH	169	/* Compute new K based on
	170	* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
	171	*/
	172	ca->bic_K = cubic_root(cube_factor
	173	* (ca->last_max_cwnd - cwnd));
df3271f3 SH	174	ca->bic_origin_point = ca->last_max_cwnd;
	175	}
	176	}
	177
e905a9ed YH	178	/* cubic function - calc*/
	179	/* calculate c * time^3 / rtt,
	180	* while considering overflow in calculation of time^3
89b3d9aa	181	* (so time^3 is done by using 64 bit)
df3271f3	182	* and without the support of division of 64bit numbers
89b3d9aa	183	* (so all divisions are done by using 32 bit)
e905a9ed YH	184	* also NOTE the unit of those veriables
	185	* time = (t - K) / 2^bictcp_HZ
	186	* c = bic_scale >> 10
df3271f3 SH	187	* rtt = (srtt >> 3) / HZ
	188	* !!! The following code does not have overflow problems,
	189	* if the cwnd < 1 million packets !!!
e905a9ed	190	*/
df3271f3 SH	191
df3271f3 SH	192	/* change the unit from HZ to bictcp_HZ */
e905a9ed	193	t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
df3271f3 SH	194	<< BICTCP_HZ) / HZ;
df3271f3 SH	195
e905a9ed	196	if (t < ca->bic_K) /* t - K */
89b3d9aa	197	offs = ca->bic_K - t;
e905a9ed YH	198	else
e905a9ed YH	199	offs = t - ca->bic_K;
df3271f3	200
89b3d9aa SH	201	/* c/rtt * (t-K)^3 */
89b3d9aa SH	202	delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
e905a9ed YH	203	if (t < ca->bic_K) /* below origin*/
	204	bic_target = ca->bic_origin_point - delta;
	205	else /* above origin*/
	206	bic_target = ca->bic_origin_point + delta;
df3271f3	207
e905a9ed YH	208	/* cubic function - calc bictcp_cnt*/
e905a9ed YH	209	if (bic_target > cwnd) {
df3271f3	210	ca->cnt = cwnd / (bic_target - cwnd);
e905a9ed YH	211	} else {
	212	ca->cnt = 100 * cwnd; /* very small increment*/
	213	}
df3271f3 SH	214
	215	if (ca->delay_min > 0) {
	216	/* max increment = Smax * rtt / 0.1 */
	217	min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
	218	if (ca->cnt < min_cnt)
	219	ca->cnt = min_cnt;
	220	}
	221
e905a9ed	222	/* slow start and low utilization */
df3271f3 SH	223	if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
	224	ca->cnt = 50;
	225
	226	/* TCP Friendly */
	227	if (tcp_friendliness) {
89b3d9aa SH	228	u32 scale = beta_scale;
89b3d9aa SH	229	delta = (cwnd * scale) >> 3;
e905a9ed YH	230	while (ca->ack_cnt > delta) { /* update tcp cwnd */
	231	ca->ack_cnt -= delta;
	232	ca->tcp_cwnd++;
df3271f3 SH	233	}
	234
	235	if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
89b3d9aa SH	236	delta = ca->tcp_cwnd - cwnd;
89b3d9aa SH	237	max_cnt = cwnd / delta;
df3271f3 SH	238	if (ca->cnt > max_cnt)
	239	ca->cnt = max_cnt;
	240	}
e905a9ed	241	}
df3271f3 SH	242
	243	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
	244	if (ca->cnt == 0) /* cannot be zero */
	245	ca->cnt = 1;
	246	}
	247
	248
	249	/* Keep track of minimum rtt */
	250	static inline void measure_delay(struct sock *sk)
	251	{
	252	const struct tcp_sock *tp = tcp_sk(sk);
	253	struct bictcp *ca = inet_csk_ca(sk);
	254	u32 delay;
	255
	256	/* No time stamp */
	257	if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) \|\|
	258	/* Discard delay samples right after fast recovery */
	259	(s32)(tcp_time_stamp - ca->epoch_start) < HZ)
	260	return;
	261
22119240	262	delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3;
df3271f3 SH	263	if (delay == 0)
	264	delay = 1;
	265
	266	/* first time call or link delay decreases */
	267	if (ca->delay_min == 0 \|\| ca->delay_min > delay)
	268	ca->delay_min = delay;
	269	}
	270
	271	static void bictcp_cong_avoid(struct sock *sk, u32 ack,
	272	u32 seq_rtt, u32 in_flight, int data_acked)
	273	{
	274	struct tcp_sock *tp = tcp_sk(sk);
	275	struct bictcp *ca = inet_csk_ca(sk);
	276
	277	if (data_acked)
	278	measure_delay(sk);
	279
	280	if (!tcp_is_cwnd_limited(sk, in_flight))
	281	return;
	282
	283	if (tp->snd_cwnd <= tp->snd_ssthresh)
	284	tcp_slow_start(tp);
	285	else {
	286	bictcp_update(ca, tp->snd_cwnd);
	287
	288	/* In dangerous area, increase slowly.
	289	* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
	290	*/
	291	if (tp->snd_cwnd_cnt >= ca->cnt) {
	292	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	293	tp->snd_cwnd++;
	294	tp->snd_cwnd_cnt = 0;
	295	} else
	296	tp->snd_cwnd_cnt++;
	297	}
	298
	299	}
	300
	301	static u32 bictcp_recalc_ssthresh(struct sock *sk)
	302	{
	303	const struct tcp_sock *tp = tcp_sk(sk);
	304	struct bictcp *ca = inet_csk_ca(sk);
	305
	306	ca->epoch_start = 0; /* end of epoch */
	307
	308	/* Wmax and fast convergence */
	309	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
	310	ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
	311	/ (2 * BICTCP_BETA_SCALE);
	312	else
	313	ca->last_max_cwnd = tp->snd_cwnd;
	314
	315	ca->loss_cwnd = tp->snd_cwnd;
	316
	317	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
	318	}
	319
	320	static u32 bictcp_undo_cwnd(struct sock *sk)
	321	{
	322	struct bictcp *ca = inet_csk_ca(sk);
	323
	324	return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
	325	}
	326
df3271f3 SH	327	static void bictcp_state(struct sock *sk, u8 new_state)
	328	{
	329	if (new_state == TCP_CA_Loss)
	330	bictcp_reset(inet_csk_ca(sk));
	331	}
	332
	333	/* Track delayed acknowledgment ratio using sliding window
	334	* ratio = (15*ratio + sample) / 16
	335	*/
	336	static void bictcp_acked(struct sock *sk, u32 cnt)
	337	{
	338	const struct inet_connection_sock *icsk = inet_csk(sk);
	339
	340	if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
	341	struct bictcp *ca = inet_csk_ca(sk);
	342	cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
	343	ca->delayed_ack += cnt;
	344	}
	345	}
	346
	347
	348	static struct tcp_congestion_ops cubictcp = {
	349	.init = bictcp_init,
	350	.ssthresh = bictcp_recalc_ssthresh,
	351	.cong_avoid = bictcp_cong_avoid,
	352	.set_state = bictcp_state,
	353	.undo_cwnd = bictcp_undo_cwnd,
df3271f3 SH	354	.pkts_acked = bictcp_acked,
	355	.owner = THIS_MODULE,
	356	.name = "cubic",
	357	};
	358
	359	static int __init cubictcp_register(void)
	360	{
74975d40	361	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
89b3d9aa SH	362
	363	/* Precompute a bunch of the scaling factors that are used per-packet
	364	* based on SRTT of 100ms
	365	*/
	366
	367	beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
	368
22119240	369	cube_rtt_scale = (bic_scale * 10); /* 1024c/rtt /
89b3d9aa SH	370
	371	/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
	372	* so K = cubic_root( (wmax-cwnd)*rtt/c )
	373	* the unit of K is bictcp_HZ=2^10, not HZ
	374	*
	375	* c = bic_scale >> 10
	376	* rtt = 100ms
	377	*
	378	* the following code has been designed and tested for
	379	* cwnd < 1 million packets
	380	* RTT < 100 seconds
	381	* HZ < 1,000,00 (corresponding to 10 nano-second)
	382	*/
	383
	384	/* 1/c * 2^2bictcp_HZ srtt */
	385	cube_factor = 1ull << (10+3BICTCP_HZ); / 2^40 */
	386
	387	/* divide by bic_scale and by constant Srtt (100ms) */
	388	do_div(cube_factor, bic_scale * 10);
	389
df3271f3 SH	390	return tcp_register_congestion_control(&cubictcp);
	391	}
	392
	393	static void __exit cubictcp_unregister(void)
	394	{
	395	tcp_unregister_congestion_control(&cubictcp);
	396	}
	397
	398	module_init(cubictcp_register);
	399	module_exit(cubictcp_unregister);
	400
	401	MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
	402	MODULE_LICENSE("GPL");
	403	MODULE_DESCRIPTION("CUBIC TCP");
	404	MODULE_VERSION("2.0");