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

/*
 * TCP Low Priority (TCP-LP)
 *
 * TCP Low Priority is a distributed algorithm whose goal is to utilize only
 *   the excess network bandwidth as compared to the ``fair share`` of
 *   bandwidth as targeted by TCP.
 *
 * As of 2.6.13, Linux supports pluggable congestion control algorithms.
 * Due to the limitation of the API, we take the following changes from
 * the original TCP-LP implementation:
 *   o We use newReno in most core CA handling. Only add some checking
 *     within cong_avoid.
 *   o Error correcting in remote HZ, therefore remote HZ will be keeped
 *     on checking and updating.
 *   o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
 *     OWD have a similar meaning as RTT. Also correct the buggy formular.
 *   o Handle reaction for Early Congestion Indication (ECI) within
 *     pkts_acked, as mentioned within pseudo code.
 *   o OWD is handled in relative format, where local time stamp will in
 *     tcp_time_stamp format.
 *
 * Original Author:
 *   Aleksandar Kuzmanovic <[email protected]>
 * Available from:
 *   http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
 * Original implementation for 2.4.19:
 *   http://www-ece.rice.edu/networks/TCP-LP/
 *
 * 2.6.x module Authors:
 *   Wong Hoi Sing, Edison <[email protected]>
 *   Hung Hing Lun, Mike <[email protected]>
 * SourceForge project page:
 *   http://tcp-lp-mod.sourceforge.net/
 */

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

/* resolution of owd */
#define LP_RESOL       TCP_TS_HZ

/**
 * enum tcp_lp_state
 * @LP_VALID_RHZ: is remote HZ valid?
 * @LP_VALID_OWD: is OWD valid?
 * @LP_WITHIN_THR: are we within threshold?
 * @LP_WITHIN_INF: are we within inference?
 *
 * TCP-LP's state flags.
 * We create this set of state flag mainly for debugging.
 */
enum tcp_lp_state {
	LP_VALID_RHZ = (1 << 0),
	LP_VALID_OWD = (1 << 1),
	LP_WITHIN_THR = (1 << 3),
	LP_WITHIN_INF = (1 << 4),
};

/**
 * struct lp
 * @flag: TCP-LP state flag
 * @sowd: smoothed OWD << 3
 * @owd_min: min OWD
 * @owd_max: max OWD
 * @owd_max_rsv: resrved max owd
 * @remote_hz: estimated remote HZ
 * @remote_ref_time: remote reference time
 * @local_ref_time: local reference time
 * @last_drop: time for last active drop
 * @inference: current inference
 *
 * TCP-LP's private struct.
 * We get the idea from original TCP-LP implementation where only left those we
 * found are really useful.
 */
struct lp {
	u32 flag;
	u32 sowd;
	u32 owd_min;
	u32 owd_max;
	u32 owd_max_rsv;
	u32 remote_hz;
	u32 remote_ref_time;
	u32 local_ref_time;
	u32 last_drop;
	u32 inference;
};

/**
 * tcp_lp_init
 *
 * Init all required variables.
 * Clone the handling from Vegas module implementation.
 */
static void tcp_lp_init(struct sock *sk)
{
	struct lp *lp = inet_csk_ca(sk);

	lp->flag = 0;
	lp->sowd = 0;
	lp->owd_min = 0xffffffff;
	lp->owd_max = 0;
	lp->owd_max_rsv = 0;
	lp->remote_hz = 0;
	lp->remote_ref_time = 0;
	lp->local_ref_time = 0;
	lp->last_drop = 0;
	lp->inference = 0;
}

/**
 * tcp_lp_cong_avoid
 *
 * Implementation of cong_avoid.
 * Will only call newReno CA when away from inference.
 * From TCP-LP's paper, this will be handled in additive increasement.
 */
static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
	struct lp *lp = inet_csk_ca(sk);

	if (!(lp->flag & LP_WITHIN_INF))
		tcp_reno_cong_avoid(sk, ack, acked);
}

/**
 * tcp_lp_remote_hz_estimator
 *
 * Estimate remote HZ.
 * We keep on updating the estimated value, where original TCP-LP
 * implementation only guest it for once and use forever.
 */
static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	s64 rhz = lp->remote_hz << 6;	/* remote HZ << 6 */
	s64 m = 0;

	/* not yet record reference time
	 * go away!! record it before come back!! */
	if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
		goto out;

	/* we can't calc remote HZ with no different!! */
	if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
	    tp->rx_opt.rcv_tsecr == lp->local_ref_time)
		goto out;

	m = TCP_TS_HZ *
	    (tp->rx_opt.rcv_tsval - lp->remote_ref_time) /
	    (tp->rx_opt.rcv_tsecr - lp->local_ref_time);
	if (m < 0)
		m = -m;

	if (rhz > 0) {
		m -= rhz >> 6;	/* m is now error in remote HZ est */
		rhz += m;	/* 63/64 old + 1/64 new */
	} else
		rhz = m << 6;

 out:
	/* record time for successful remote HZ calc */
	if ((rhz >> 6) > 0)
		lp->flag |= LP_VALID_RHZ;
	else
		lp->flag &= ~LP_VALID_RHZ;

	/* record reference time stamp */
	lp->remote_ref_time = tp->rx_opt.rcv_tsval;
	lp->local_ref_time = tp->rx_opt.rcv_tsecr;

	return rhz >> 6;
}

/**
 * tcp_lp_owd_calculator
 *
 * Calculate one way delay (in relative format).
 * Original implement OWD as minus of remote time difference to local time
 * difference directly. As this time difference just simply equal to RTT, when
 * the network status is stable, remote RTT will equal to local RTT, and result
 * OWD into zero.
 * It seems to be a bug and so we fixed it.
 */
static u32 tcp_lp_owd_calculator(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	s64 owd = 0;

	lp->remote_hz = tcp_lp_remote_hz_estimator(sk);

	if (lp->flag & LP_VALID_RHZ) {
		owd =
		    tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
		    tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ);
		if (owd < 0)
			owd = -owd;
	}

	if (owd > 0)
		lp->flag |= LP_VALID_OWD;
	else
		lp->flag &= ~LP_VALID_OWD;

	return owd;
}

/**
 * tcp_lp_rtt_sample
 *
 * Implementation or rtt_sample.
 * Will take the following action,
 *   1. calc OWD,
 *   2. record the min/max OWD,
 *   3. calc smoothed OWD (SOWD).
 * Most ideas come from the original TCP-LP implementation.
 */
static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
{
	struct lp *lp = inet_csk_ca(sk);
	s64 mowd = tcp_lp_owd_calculator(sk);

	/* sorry that we don't have valid data */
	if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
		return;

	/* record the next min owd */
	if (mowd < lp->owd_min)
		lp->owd_min = mowd;

	/* always forget the max of the max
	 * we just set owd_max as one below it */
	if (mowd > lp->owd_max) {
		if (mowd > lp->owd_max_rsv) {
			if (lp->owd_max_rsv == 0)
				lp->owd_max = mowd;
			else
				lp->owd_max = lp->owd_max_rsv;
			lp->owd_max_rsv = mowd;
		} else
			lp->owd_max = mowd;
	}

	/* calc for smoothed owd */
	if (lp->sowd != 0) {
		mowd -= lp->sowd >> 3;	/* m is now error in owd est */
		lp->sowd += mowd;	/* owd = 7/8 owd + 1/8 new */
	} else
		lp->sowd = mowd << 3;	/* take the measured time be owd */
}

/**
 * tcp_lp_pkts_acked
 *
 * Implementation of pkts_acked.
 * Deal with active drop under Early Congestion Indication.
 * Only drop to half and 1 will be handle, because we hope to use back
 * newReno in increase case.
 * We work it out by following the idea from TCP-LP's paper directly
 */
static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	u32 now = tcp_time_stamp(tp);
	u32 delta;

	if (sample->rtt_us > 0)
		tcp_lp_rtt_sample(sk, sample->rtt_us);

	/* calc inference */
	delta = now - tp->rx_opt.rcv_tsecr;
	if ((s32)delta > 0)
		lp->inference = 3 * delta;

	/* test if within inference */
	if (lp->last_drop && (now - lp->last_drop < lp->inference))
		lp->flag |= LP_WITHIN_INF;
	else
		lp->flag &= ~LP_WITHIN_INF;

	/* test if within threshold */
	if (lp->sowd >> 3 <
	    lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
		lp->flag |= LP_WITHIN_THR;
	else
		lp->flag &= ~LP_WITHIN_THR;

	pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
		 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
		 lp->sowd >> 3);

	if (lp->flag & LP_WITHIN_THR)
		return;

	/* FIXME: try to reset owd_min and owd_max here
	 * so decrease the chance the min/max is no longer suitable
	 * and will usually within threshold when whithin inference */
	lp->owd_min = lp->sowd >> 3;
	lp->owd_max = lp->sowd >> 2;
	lp->owd_max_rsv = lp->sowd >> 2;

	/* happened within inference
	 * drop snd_cwnd into 1 */
	if (lp->flag & LP_WITHIN_INF)
		tp->snd_cwnd = 1U;

	/* happened after inference
	 * cut snd_cwnd into half */
	else
		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);

	/* record this drop time */
	lp->last_drop = now;
}

static struct tcp_congestion_ops tcp_lp __read_mostly = {
	.init = tcp_lp_init,
	.ssthresh = tcp_reno_ssthresh,
	.undo_cwnd = tcp_reno_undo_cwnd,
	.cong_avoid = tcp_lp_cong_avoid,
	.pkts_acked = tcp_lp_pkts_acked,

	.owner = THIS_MODULE,
	.name = "lp"
};

static int __init tcp_lp_register(void)
{
	BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
	return tcp_register_congestion_control(&tcp_lp);
}

static void __exit tcp_lp_unregister(void)
{
	tcp_unregister_congestion_control(&tcp_lp);
}

module_init(tcp_lp_register);
module_exit(tcp_lp_unregister);

MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Low Priority");
Commit	Line	Data
7c106d7e WHSE	1	/*
	2	* TCP Low Priority (TCP-LP)
	3	*
	4	* TCP Low Priority is a distributed algorithm whose goal is to utilize only
	5	* the excess network bandwidth as compared to the ``fair share`` of
3795da47	6	* bandwidth as targeted by TCP.
7c106d7e	7	*
7c106d7e WHSE	8	* As of 2.6.13, Linux supports pluggable congestion control algorithms.
	9	* Due to the limitation of the API, we take the following changes from
	10	* the original TCP-LP implementation:
	11	* o We use newReno in most core CA handling. Only add some checking
	12	* within cong_avoid.
	13	* o Error correcting in remote HZ, therefore remote HZ will be keeped
	14	* on checking and updating.
25985edc	15	* o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
7c106d7e WHSE	16	* OWD have a similar meaning as RTT. Also correct the buggy formular.
	17	* o Handle reaction for Early Congestion Indication (ECI) within
	18	* pkts_acked, as mentioned within pseudo code.
	19	* o OWD is handled in relative format, where local time stamp will in
	20	* tcp_time_stamp format.
	21	*
3795da47 WHSE	22	* Original Author:
	23	* Aleksandar Kuzmanovic <[email protected]>
	24	* Available from:
	25	* http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
	26	* Original implementation for 2.4.19:
	27	* http://www-ece.rice.edu/networks/TCP-LP/
7c106d7e	28	*
3795da47 WHSE	29	* 2.6.x module Authors:
	30	* Wong Hoi Sing, Edison <[email protected]>
	31	* Hung Hing Lun, Mike <[email protected]>
	32	* SourceForge project page:
	33	* http://tcp-lp-mod.sourceforge.net/
7c106d7e WHSE	34	*/
7c106d7e WHSE	35
7c106d7e WHSE	36	#include <linux/module.h>
	37	#include <net/tcp.h>
	38
	39	/* resolution of owd */
9a568de4	40	#define LP_RESOL TCP_TS_HZ
7c106d7e WHSE	41
	42	/**
	43	* enum tcp_lp_state
	44	* @LP_VALID_RHZ: is remote HZ valid?
	45	* @LP_VALID_OWD: is OWD valid?
	46	* @LP_WITHIN_THR: are we within threshold?
	47	* @LP_WITHIN_INF: are we within inference?
	48	*
	49	* TCP-LP's state flags.
	50	* We create this set of state flag mainly for debugging.
	51	*/
	52	enum tcp_lp_state {
	53	LP_VALID_RHZ = (1 << 0),
	54	LP_VALID_OWD = (1 << 1),
	55	LP_WITHIN_THR = (1 << 3),
	56	LP_WITHIN_INF = (1 << 4),
	57	};
	58
	59	/**
	60	* struct lp
	61	* @flag: TCP-LP state flag
	62	* @sowd: smoothed OWD << 3
	63	* @owd_min: min OWD
	64	* @owd_max: max OWD
	65	* @owd_max_rsv: resrved max owd
	66	* @remote_hz: estimated remote HZ
	67	* @remote_ref_time: remote reference time
	68	* @local_ref_time: local reference time
	69	* @last_drop: time for last active drop
	70	* @inference: current inference
	71	*
	72	* TCP-LP's private struct.
	73	* We get the idea from original TCP-LP implementation where only left those we
	74	* found are really useful.
	75	*/
	76	struct lp {
	77	u32 flag;
	78	u32 sowd;
	79	u32 owd_min;
	80	u32 owd_max;
	81	u32 owd_max_rsv;
	82	u32 remote_hz;
	83	u32 remote_ref_time;
	84	u32 local_ref_time;
	85	u32 last_drop;
	86	u32 inference;
	87	};
	88
	89	/**
	90	* tcp_lp_init
	91	*
	92	* Init all required variables.
	93	* Clone the handling from Vegas module implementation.
	94	*/
	95	static void tcp_lp_init(struct sock *sk)
	96	{
	97	struct lp *lp = inet_csk_ca(sk);
	98
	99	lp->flag = 0;
	100	lp->sowd = 0;
	101	lp->owd_min = 0xffffffff;
	102	lp->owd_max = 0;
	103	lp->owd_max_rsv = 0;
	104	lp->remote_hz = 0;
105	lp->remote_ref_time = 0;
106	lp->local_ref_time = 0;
107	lp->last_drop = 0;
108	lp->inference = 0;
109	}
110
111	/**
112	* tcp_lp_cong_avoid
113	*
114	* Implementation of cong_avoid.
115	* Will only call newReno CA when away from inference.
116	* From TCP-LP's paper, this will be handled in additive increasement.
117	*/
24901551	118	static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
7c106d7e WHSE	119	{
	120	struct lp *lp = inet_csk_ca(sk);
	121
	122	if (!(lp->flag & LP_WITHIN_INF))
24901551	123	tcp_reno_cong_avoid(sk, ack, acked);
7c106d7e WHSE	124	}
	125
	126	/**
	127	* tcp_lp_remote_hz_estimator
	128	*
	129	* Estimate remote HZ.
	130	* We keep on updating the estimated value, where original TCP-LP
	131	* implementation only guest it for once and use forever.
	132	*/
	133	static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
	134	{
	135	struct tcp_sock *tp = tcp_sk(sk);
	136	struct lp *lp = inet_csk_ca(sk);
	137	s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */
	138	s64 m = 0;
	139
	140	/* not yet record reference time
	141	* go away!! record it before come back!! */
	142	if (lp->remote_ref_time == 0 \|\| lp->local_ref_time == 0)
	143	goto out;
	144
	145	/* we can't calc remote HZ with no different!! */
9d4fb27d JP	146	if (tp->rx_opt.rcv_tsval == lp->remote_ref_time \|\|
9d4fb27d JP	147	tp->rx_opt.rcv_tsecr == lp->local_ref_time)
7c106d7e WHSE	148	goto out;
7c106d7e WHSE	149
9a568de4 ED	150	m = TCP_TS_HZ *
	151	(tp->rx_opt.rcv_tsval - lp->remote_ref_time) /
	152	(tp->rx_opt.rcv_tsecr - lp->local_ref_time);
7c106d7e WHSE	153	if (m < 0)
	154	m = -m;
	155
3795da47	156	if (rhz > 0) {
7c106d7e WHSE	157	m -= rhz >> 6; /* m is now error in remote HZ est */
	158	rhz += m; /* 63/64 old + 1/64 new */
	159	} else
	160	rhz = m << 6;
	161
3795da47	162	out:
7c106d7e	163	/* record time for successful remote HZ calc */
bfbea8a8	164	if ((rhz >> 6) > 0)
3795da47 WHSE	165	lp->flag \|= LP_VALID_RHZ;
	166	else
	167	lp->flag &= ~LP_VALID_RHZ;
7c106d7e	168
7c106d7e WHSE	169	/* record reference time stamp */
	170	lp->remote_ref_time = tp->rx_opt.rcv_tsval;
	171	lp->local_ref_time = tp->rx_opt.rcv_tsecr;
	172
	173	return rhz >> 6;
	174	}
	175
	176	/**
	177	* tcp_lp_owd_calculator
	178	*
	179	* Calculate one way delay (in relative format).
	180	* Original implement OWD as minus of remote time difference to local time
	181	* difference directly. As this time difference just simply equal to RTT, when
	182	* the network status is stable, remote RTT will equal to local RTT, and result
	183	* OWD into zero.
	184	* It seems to be a bug and so we fixed it.
	185	*/
	186	static u32 tcp_lp_owd_calculator(struct sock *sk)
	187	{
	188	struct tcp_sock *tp = tcp_sk(sk);
	189	struct lp *lp = inet_csk_ca(sk);
	190	s64 owd = 0;
	191
	192	lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
	193
	194	if (lp->flag & LP_VALID_RHZ) {
	195	owd =
	196	tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
9a568de4	197	tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ);
7c106d7e WHSE	198	if (owd < 0)
	199	owd = -owd;
	200	}
	201
	202	if (owd > 0)
	203	lp->flag \|= LP_VALID_OWD;
	204	else
	205	lp->flag &= ~LP_VALID_OWD;
	206
	207	return owd;
	208	}
	209
	210	/**
	211	* tcp_lp_rtt_sample
	212	*
	213	* Implementation or rtt_sample.
	214	* Will take the following action,
	215	* 1. calc OWD,
	216	* 2. record the min/max OWD,
	217	* 3. calc smoothed OWD (SOWD).
	218	* Most ideas come from the original TCP-LP implementation.
	219	*/
164891aa	220	static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
7c106d7e WHSE	221	{
	222	struct lp *lp = inet_csk_ca(sk);
	223	s64 mowd = tcp_lp_owd_calculator(sk);
	224
	225	/* sorry that we don't have valid data */
	226	if (!(lp->flag & LP_VALID_RHZ) \|\| !(lp->flag & LP_VALID_OWD))
	227	return;
	228
	229	/* record the next min owd */
	230	if (mowd < lp->owd_min)
	231	lp->owd_min = mowd;
	232
	233	/* always forget the max of the max
	234	* we just set owd_max as one below it */
	235	if (mowd > lp->owd_max) {
	236	if (mowd > lp->owd_max_rsv) {
	237	if (lp->owd_max_rsv == 0)
	238	lp->owd_max = mowd;
	239	else
	240	lp->owd_max = lp->owd_max_rsv;
	241	lp->owd_max_rsv = mowd;
	242	} else
	243	lp->owd_max = mowd;
	244	}
	245
	246	/* calc for smoothed owd */
	247	if (lp->sowd != 0) {
	248	mowd -= lp->sowd >> 3; /* m is now error in owd est */
	249	lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */
	250	} else
	251	lp->sowd = mowd << 3; /* take the measured time be owd */
	252	}
	253
	254	/**
	255	* tcp_lp_pkts_acked
	256	*
	257	* Implementation of pkts_acked.
	258	* Deal with active drop under Early Congestion Indication.
	259	* Only drop to half and 1 will be handle, because we hope to use back
	260	* newReno in increase case.
	261	* We work it out by following the idea from TCP-LP's paper directly
	262	*/
756ee172	263	static void tcp_lp_pkts_acked(struct sock sk, const struct ack_sample sample)
7c106d7e WHSE	264	{
	265	struct tcp_sock *tp = tcp_sk(sk);
	266	struct lp *lp = inet_csk_ca(sk);
9a568de4	267	u32 now = tcp_time_stamp(tp);
a9f11f96	268	u32 delta;
7c106d7e	269
756ee172 LB	270	if (sample->rtt_us > 0)
756ee172 LB	271	tcp_lp_rtt_sample(sk, sample->rtt_us);
164891aa	272
7c106d7e	273	/* calc inference */
46bf466f	274	delta = now - tp->rx_opt.rcv_tsecr;
a9f11f96 ED	275	if ((s32)delta > 0)
a9f11f96 ED	276	lp->inference = 3 * delta;
7c106d7e WHSE	277
7c106d7e WHSE	278	/* test if within inference */
46bf466f	279	if (lp->last_drop && (now - lp->last_drop < lp->inference))
7c106d7e WHSE	280	lp->flag \|= LP_WITHIN_INF;
	281	else
	282	lp->flag &= ~LP_WITHIN_INF;
	283
	284	/* test if within threshold */
	285	if (lp->sowd >> 3 <
	286	lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
	287	lp->flag \|= LP_WITHIN_THR;
	288	else
	289	lp->flag &= ~LP_WITHIN_THR;
	290
	291	pr_debug("TCP-LP: %05o\|%5u\|%5u\|%15u\|%15u\|%15u\n", lp->flag,
	292	tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
	293	lp->sowd >> 3);
	294
	295	if (lp->flag & LP_WITHIN_THR)
	296	return;
	297
	298	/* FIXME: try to reset owd_min and owd_max here
	299	* so decrease the chance the min/max is no longer suitable
	300	* and will usually within threshold when whithin inference */
	301	lp->owd_min = lp->sowd >> 3;
	302	lp->owd_max = lp->sowd >> 2;
	303	lp->owd_max_rsv = lp->sowd >> 2;
	304
	305	/* happened within inference
	306	* drop snd_cwnd into 1 */
	307	if (lp->flag & LP_WITHIN_INF)
	308	tp->snd_cwnd = 1U;
	309
	310	/* happened after inference
	311	* cut snd_cwnd into half */
	312	else
	313	tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
	314
	315	/* record this drop time */
46bf466f	316	lp->last_drop = now;
7c106d7e WHSE	317	}
7c106d7e WHSE	318
a252bebe	319	static struct tcp_congestion_ops tcp_lp __read_mostly = {
7c106d7e WHSE	320	.init = tcp_lp_init,
7c106d7e WHSE	321	.ssthresh = tcp_reno_ssthresh,
e9799183	322	.undo_cwnd = tcp_reno_undo_cwnd,
7c106d7e	323	.cong_avoid = tcp_lp_cong_avoid,
7c106d7e WHSE	324	.pkts_acked = tcp_lp_pkts_acked,
	325
	326	.owner = THIS_MODULE,
	327	.name = "lp"
	328	};
	329
	330	static int __init tcp_lp_register(void)
	331	{
29896972	332	BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
7c106d7e WHSE	333	return tcp_register_congestion_control(&tcp_lp);
	334	}
	335
	336	static void __exit tcp_lp_unregister(void)
	337	{
	338	tcp_unregister_congestion_control(&tcp_lp);
	339	}
	340
	341	module_init(tcp_lp_register);
	342	module_exit(tcp_lp_unregister);
	343
3795da47	344	MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
7c106d7e WHSE	345	MODULE_LICENSE("GPL");
7c106d7e WHSE	346	MODULE_DESCRIPTION("TCP Low Priority");