[GitHub/mt8127/android_kernel_alcatel_ttab.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/config.h>
#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 = 1;
static int max_increment = 16;
static int beta = 819;		/* = 819/1024 (BICTCP_BETA_SCALE) */
static int initial_ssthresh = 100;
static int bic_scale = 41;
static int tcp_friendliness = 1;

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

/* 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");


/* 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;
}

/* 65536 times the cubic root */
static const u64 cubic_table[8]
	= {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367};

/*
 * calculate the cubic root of x
 * the basic idea is that x can be expressed as i*8^j
 * so cubic_root(x) = cubic_root(i)*2^j
 *  in the following code, x is i, and y is 2^j
 *  because of integer calculation, there are errors in calculation
 *  so finally use binary search to find out the exact solution
 */
static u32 cubic_root(u64 x)
{
        u64 y, app, target, start, end, mid, start_diff, end_diff;

        if (x == 0)
                return 0;

        target = x;

        /* first estimate lower and upper bound */
        y = 1;
        while (x >= 8){
                x = (x >> 3);
                y = (y << 1);
        }
        start = (y*cubic_table[x])>>16;
        if (x==7)
                end = (y<<1);
        else
                end = (y*cubic_table[x+1]+65535)>>16;

        /* binary search for more accurate one */
        while (start < end-1) {
                mid = (start+end) >> 1;
                app = mid*mid*mid;
                if (app < target)
                        start = mid;
                else if (app > target)
                        end = mid;
                else
                        return mid;
        }

        /* find the most accurate one from start and end */
        app = start*start*start;
        if (app < target)
                start_diff = target - app;
        else
                start_diff = app - target;
        app = end*end*end;
        if (app < target)
                end_diff = target - app;
        else
                end_diff = app - target;

        if (start_diff < end_diff)
                return (u32)start;
        else
                return (u32)end;
}

/*
 * 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 - 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;
	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 u32 bictcp_min_cwnd(struct sock *sk)
{
	return tcp_sk(sk)->snd_ssthresh;
}

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,
	.min_cwnd	= bictcp_min_cwnd,
	.pkts_acked     = bictcp_acked,
	.owner		= THIS_MODULE,
	.name		= "cubic",
};

static int __init cubictcp_register(void)
{
	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 << 3) / 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
	15	#include <linux/config.h>
	16	#include <linux/mm.h>
	17	#include <linux/module.h>
	18	#include <net/tcp.h>
89b3d9aa	19	#include <asm/div64.h>
df3271f3 SH	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	#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
	29
	30	static int fast_convergence = 1;
	31	static int max_increment = 16;
	32	static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
	33	static int initial_ssthresh = 100;
	34	static int bic_scale = 41;
	35	static int tcp_friendliness = 1;
	36
89b3d9aa SH	37	static u32 cube_rtt_scale;
	38	static u32 beta_scale;
	39	static u64 cube_factor;
	40
	41	/* Note parameters that are used for precomputing scale factors are read-only */
df3271f3 SH	42	module_param(fast_convergence, int, 0644);
	43	MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
	44	module_param(max_increment, int, 0644);
	45	MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
89b3d9aa	46	module_param(beta, int, 0444);
df3271f3 SH	47	MODULE_PARM_DESC(beta, "beta for multiplicative increase");
	48	module_param(initial_ssthresh, int, 0644);
	49	MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
89b3d9aa	50	module_param(bic_scale, int, 0444);
df3271f3 SH	51	MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
	52	module_param(tcp_friendliness, int, 0644);
	53	MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
	54
	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
	96	/* 65536 times the cubic root */
	97	static const u64 cubic_table[8]
	98	= {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367};
	99
	100	/*
	101	* calculate the cubic root of x
	102	* the basic idea is that x can be expressed as i*8^j
	103	* so cubic_root(x) = cubic_root(i)*2^j
	104	* in the following code, x is i, and y is 2^j
	105	* because of integer calculation, there are errors in calculation
	106	* so finally use binary search to find out the exact solution
	107	*/
	108	static u32 cubic_root(u64 x)
	109	{
	110	u64 y, app, target, start, end, mid, start_diff, end_diff;
	111
	112	if (x == 0)
	113	return 0;
	114
115	target = x;
116
117	/* first estimate lower and upper bound */
118	y = 1;
119	while (x >= 8){
120	x = (x >> 3);
121	y = (y << 1);
122	}
123	start = (y*cubic_table[x])>>16;
124	if (x==7)
125	end = (y<<1);
126	else
127	end = (y*cubic_table[x+1]+65535)>>16;
128
129	/* binary search for more accurate one */
130	while (start < end-1) {
131	mid = (start+end) >> 1;
132	app = midmidmid;
133	if (app < target)
134	start = mid;
135	else if (app > target)
136	end = mid;
137	else
138	return mid;
139	}
140
141	/* find the most accurate one from start and end */
142	app = startstartstart;
143	if (app < target)
144	start_diff = target - app;
145	else
146	start_diff = app - target;
147	app = endendend;
148	if (app < target)
149	end_diff = target - app;
150	else
151	end_diff = app - target;
152
153	if (start_diff < end_diff)
154	return (u32)start;
155	else
156	return (u32)end;
157	}
158
df3271f3 SH	159	/*
	160	* Compute congestion window to use.
	161	*/
	162	static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
	163	{
89b3d9aa SH	164	u64 offs;
89b3d9aa SH	165	u32 delta, t, bic_target, min_cnt, max_cnt;
df3271f3 SH	166
	167	ca->ack_cnt++; /* count the number of ACKs */
	168
	169	if (ca->last_cwnd == cwnd &&
	170	(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
	171	return;
	172
	173	ca->last_cwnd = cwnd;
	174	ca->last_time = tcp_time_stamp;
	175
df3271f3 SH	176	if (ca->epoch_start == 0) {
	177	ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
	178	ca->ack_cnt = 1; /* start counting */
	179	ca->tcp_cwnd = cwnd; /* syn with cubic */
	180
	181	if (ca->last_max_cwnd <= cwnd) {
	182	ca->bic_K = 0;
	183	ca->bic_origin_point = cwnd;
	184	} else {
89b3d9aa SH	185	/* Compute new K based on
	186	* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
	187	*/
	188	ca->bic_K = cubic_root(cube_factor
	189	* (ca->last_max_cwnd - cwnd));
df3271f3 SH	190	ca->bic_origin_point = ca->last_max_cwnd;
	191	}
	192	}
	193
	194	/* cubic function - calc*/
	195	/* calculate c * time^3 / rtt,
	196	* while considering overflow in calculation of time^3
89b3d9aa	197	* (so time^3 is done by using 64 bit)
df3271f3	198	* and without the support of division of 64bit numbers
89b3d9aa	199	* (so all divisions are done by using 32 bit)
df3271f3 SH	200	* also NOTE the unit of those veriables
	201	* time = (t - K) / 2^bictcp_HZ
	202	* c = bic_scale >> 10
	203	* rtt = (srtt >> 3) / HZ
	204	* !!! The following code does not have overflow problems,
	205	* if the cwnd < 1 million packets !!!
	206	*/
	207
	208	/* change the unit from HZ to bictcp_HZ */
	209	t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start)
	210	<< BICTCP_HZ) / HZ;
	211
	212	if (t < ca->bic_K) /* t - K */
89b3d9aa	213	offs = ca->bic_K - t;
df3271f3	214	else
89b3d9aa	215	offs = t - ca->bic_K;
df3271f3	216
89b3d9aa SH	217	/* c/rtt * (t-K)^3 */
89b3d9aa SH	218	delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
df3271f3	219	if (t < ca->bic_K) /* below origin*/
89b3d9aa	220	bic_target = ca->bic_origin_point - delta;
df3271f3	221	else /* above origin*/
89b3d9aa	222	bic_target = ca->bic_origin_point + delta;
df3271f3 SH	223
	224	/* cubic function - calc bictcp_cnt*/
	225	if (bic_target > cwnd) {
	226	ca->cnt = cwnd / (bic_target - cwnd);
	227	} else {
	228	ca->cnt = 100 * cwnd; /* very small increment*/
	229	}
	230
	231	if (ca->delay_min > 0) {
	232	/* max increment = Smax * rtt / 0.1 */
	233	min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
	234	if (ca->cnt < min_cnt)
	235	ca->cnt = min_cnt;
	236	}
	237
	238	/* slow start and low utilization */
	239	if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
	240	ca->cnt = 50;
	241
	242	/* TCP Friendly */
	243	if (tcp_friendliness) {
89b3d9aa SH	244	u32 scale = beta_scale;
	245	delta = (cwnd * scale) >> 3;
	246	while (ca->ack_cnt > delta) { /* update tcp cwnd */
	247	ca->ack_cnt -= delta;
df3271f3 SH	248	ca->tcp_cwnd++;
	249	}
	250
	251	if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
89b3d9aa SH	252	delta = ca->tcp_cwnd - cwnd;
89b3d9aa SH	253	max_cnt = cwnd / delta;
df3271f3 SH	254	if (ca->cnt > max_cnt)
	255	ca->cnt = max_cnt;
	256	}
	257	}
	258
	259	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
	260	if (ca->cnt == 0) /* cannot be zero */
	261	ca->cnt = 1;
	262	}
	263
	264
	265	/* Keep track of minimum rtt */
	266	static inline void measure_delay(struct sock *sk)
	267	{
	268	const struct tcp_sock *tp = tcp_sk(sk);
	269	struct bictcp *ca = inet_csk_ca(sk);
	270	u32 delay;
	271
	272	/* No time stamp */
	273	if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) \|\|
	274	/* Discard delay samples right after fast recovery */
	275	(s32)(tcp_time_stamp - ca->epoch_start) < HZ)
	276	return;
	277
	278	delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
	279	if (delay == 0)
	280	delay = 1;
	281
	282	/* first time call or link delay decreases */
	283	if (ca->delay_min == 0 \|\| ca->delay_min > delay)
	284	ca->delay_min = delay;
	285	}
	286
	287	static void bictcp_cong_avoid(struct sock *sk, u32 ack,
	288	u32 seq_rtt, u32 in_flight, int data_acked)
	289	{
	290	struct tcp_sock *tp = tcp_sk(sk);
	291	struct bictcp *ca = inet_csk_ca(sk);
	292
	293	if (data_acked)
	294	measure_delay(sk);
	295
	296	if (!tcp_is_cwnd_limited(sk, in_flight))
	297	return;
	298
	299	if (tp->snd_cwnd <= tp->snd_ssthresh)
	300	tcp_slow_start(tp);
	301	else {
	302	bictcp_update(ca, tp->snd_cwnd);
	303
	304	/* In dangerous area, increase slowly.
	305	* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
	306	*/
	307	if (tp->snd_cwnd_cnt >= ca->cnt) {
	308	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	309	tp->snd_cwnd++;
	310	tp->snd_cwnd_cnt = 0;
	311	} else
	312	tp->snd_cwnd_cnt++;
	313	}
	314
	315	}
	316
	317	static u32 bictcp_recalc_ssthresh(struct sock *sk)
318	{
319	const struct tcp_sock *tp = tcp_sk(sk);
320	struct bictcp *ca = inet_csk_ca(sk);
321
322	ca->epoch_start = 0; /* end of epoch */
323
324	/* Wmax and fast convergence */
325	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
326	ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
327	/ (2 * BICTCP_BETA_SCALE);
328	else
329	ca->last_max_cwnd = tp->snd_cwnd;
330
331	ca->loss_cwnd = tp->snd_cwnd;
332
333	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
334	}
335
336	static u32 bictcp_undo_cwnd(struct sock *sk)
337	{
338	struct bictcp *ca = inet_csk_ca(sk);
339
340	return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
341	}
342
343	static u32 bictcp_min_cwnd(struct sock *sk)
344	{
345	return tcp_sk(sk)->snd_ssthresh;
346	}
347
348	static void bictcp_state(struct sock *sk, u8 new_state)
349	{
350	if (new_state == TCP_CA_Loss)
351	bictcp_reset(inet_csk_ca(sk));
352	}
353
354	/* Track delayed acknowledgment ratio using sliding window
355	* ratio = (15*ratio + sample) / 16
356	*/
357	static void bictcp_acked(struct sock *sk, u32 cnt)
358	{
359	const struct inet_connection_sock *icsk = inet_csk(sk);
360
361	if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
362	struct bictcp *ca = inet_csk_ca(sk);
363	cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
364	ca->delayed_ack += cnt;
365	}
366	}
367
368
369	static struct tcp_congestion_ops cubictcp = {
370	.init = bictcp_init,
371	.ssthresh = bictcp_recalc_ssthresh,
372	.cong_avoid = bictcp_cong_avoid,
373	.set_state = bictcp_state,
374	.undo_cwnd = bictcp_undo_cwnd,
375	.min_cwnd = bictcp_min_cwnd,
376	.pkts_acked = bictcp_acked,
377	.owner = THIS_MODULE,
378	.name = "cubic",
379	};
380
381	static int __init cubictcp_register(void)
382	{
383	BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
89b3d9aa SH	384
	385	/* Precompute a bunch of the scaling factors that are used per-packet
	386	* based on SRTT of 100ms
	387	*/
	388
	389	beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
	390
	391	cube_rtt_scale = (bic_scale << 3) / 10; /* 1024c/rtt /
	392
	393	/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
	394	* so K = cubic_root( (wmax-cwnd)*rtt/c )
	395	* the unit of K is bictcp_HZ=2^10, not HZ
	396	*
	397	* c = bic_scale >> 10
	398	* rtt = 100ms
	399	*
	400	* the following code has been designed and tested for
	401	* cwnd < 1 million packets
	402	* RTT < 100 seconds
	403	* HZ < 1,000,00 (corresponding to 10 nano-second)
	404	*/
	405
	406	/* 1/c * 2^2bictcp_HZ srtt */
	407	cube_factor = 1ull << (10+3BICTCP_HZ); / 2^40 */
	408
	409	/* divide by bic_scale and by constant Srtt (100ms) */
	410	do_div(cube_factor, bic_scale * 10);
	411
df3271f3 SH	412	return tcp_register_congestion_control(&cubictcp);
	413	}
	414
	415	static void __exit cubictcp_unregister(void)
	416	{
	417	tcp_unregister_congestion_control(&cubictcp);
	418	}
	419
	420	module_init(cubictcp_register);
	421	module_exit(cubictcp_unregister);
	422
	423	MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
	424	MODULE_LICENSE("GPL");
	425	MODULE_DESCRIPTION("CUBIC TCP");
	426	MODULE_VERSION("2.0");