[linux-2.6-block.git] / net / ipv4 / tcp_cong.c

/*
 * Plugable TCP congestion control support and newReno
 * congestion control.
 * Based on ideas from I/O scheduler suport and Web100.
 *
 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
 */

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

int sysctl_tcp_max_ssthresh = 0;

static DEFINE_SPINLOCK(tcp_cong_list_lock);
static LIST_HEAD(tcp_cong_list);

/* Simple linear search, don't expect many entries! */
static struct tcp_congestion_ops *tcp_ca_find(const char *name)
{
	struct tcp_congestion_ops *e;

	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
		if (strcmp(e->name, name) == 0)
			return e;
	}

	return NULL;
}

/*
 * Attach new congestion control algorithm to the list
 * of available options.
 */
int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
{
	int ret = 0;

	/* all algorithms must implement ssthresh and cong_avoid ops */
	if (!ca->ssthresh || !ca->cong_avoid) {
		printk(KERN_ERR "TCP %s does not implement required ops\n",
		       ca->name);
		return -EINVAL;
	}

	spin_lock(&tcp_cong_list_lock);
	if (tcp_ca_find(ca->name)) {
		printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
		ret = -EEXIST;
	} else {
		list_add_tail_rcu(&ca->list, &tcp_cong_list);
		printk(KERN_INFO "TCP %s registered\n", ca->name);
	}
	spin_unlock(&tcp_cong_list_lock);

	return ret;
}
EXPORT_SYMBOL_GPL(tcp_register_congestion_control);

/*
 * Remove congestion control algorithm, called from
 * the module's remove function.  Module ref counts are used
 * to ensure that this can't be done till all sockets using
 * that method are closed.
 */
void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
{
	spin_lock(&tcp_cong_list_lock);
	list_del_rcu(&ca->list);
	spin_unlock(&tcp_cong_list_lock);
}
EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);

/* Assign choice of congestion control. */
void tcp_init_congestion_control(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_congestion_ops *ca;

	/* if no choice made yet assign the current value set as default */
	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
		rcu_read_lock();
		list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
			if (try_module_get(ca->owner)) {
				icsk->icsk_ca_ops = ca;
				break;
			}

			/* fallback to next available */
		}
		rcu_read_unlock();
	}

	if (icsk->icsk_ca_ops->init)
		icsk->icsk_ca_ops->init(sk);
}

/* Manage refcounts on socket close. */
void tcp_cleanup_congestion_control(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);

	if (icsk->icsk_ca_ops->release)
		icsk->icsk_ca_ops->release(sk);
	module_put(icsk->icsk_ca_ops->owner);
}

/* Used by sysctl to change default congestion control */
int tcp_set_default_congestion_control(const char *name)
{
	struct tcp_congestion_ops *ca;
	int ret = -ENOENT;

	spin_lock(&tcp_cong_list_lock);
	ca = tcp_ca_find(name);
#ifdef CONFIG_MODULES
	if (!ca && capable(CAP_NET_ADMIN)) {
		spin_unlock(&tcp_cong_list_lock);

		request_module("tcp_%s", name);
		spin_lock(&tcp_cong_list_lock);
		ca = tcp_ca_find(name);
	}
#endif

	if (ca) {
		ca->flags |= TCP_CONG_NON_RESTRICTED;	/* default is always allowed */
		list_move(&ca->list, &tcp_cong_list);
		ret = 0;
	}
	spin_unlock(&tcp_cong_list_lock);

	return ret;
}

/* Set default value from kernel configuration at bootup */
static int __init tcp_congestion_default(void)
{
	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
}
late_initcall(tcp_congestion_default);


/* Build string with list of available congestion control values */
void tcp_get_available_congestion_control(char *buf, size_t maxlen)
{
	struct tcp_congestion_ops *ca;
	size_t offs = 0;

	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
		offs += snprintf(buf + offs, maxlen - offs,
				 "%s%s",
				 offs == 0 ? "" : " ", ca->name);

	}
	rcu_read_unlock();
}

/* Get current default congestion control */
void tcp_get_default_congestion_control(char *name)
{
	struct tcp_congestion_ops *ca;
	/* We will always have reno... */
	BUG_ON(list_empty(&tcp_cong_list));

	rcu_read_lock();
	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	rcu_read_unlock();
}

/* Built list of non-restricted congestion control values */
void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
{
	struct tcp_congestion_ops *ca;
	size_t offs = 0;

	*buf = '\0';
	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
		if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
			continue;
		offs += snprintf(buf + offs, maxlen - offs,
				 "%s%s",
				 offs == 0 ? "" : " ", ca->name);

	}
	rcu_read_unlock();
}

/* Change list of non-restricted congestion control */
int tcp_set_allowed_congestion_control(char *val)
{
	struct tcp_congestion_ops *ca;
	char *saved_clone, *clone, *name;
	int ret = 0;

	saved_clone = clone = kstrdup(val, GFP_USER);
	if (!clone)
		return -ENOMEM;

	spin_lock(&tcp_cong_list_lock);
	/* pass 1 check for bad entries */
	while ((name = strsep(&clone, " ")) && *name) {
		ca = tcp_ca_find(name);
		if (!ca) {
			ret = -ENOENT;
			goto out;
		}
	}

	/* pass 2 clear old values */
	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
		ca->flags &= ~TCP_CONG_NON_RESTRICTED;

	/* pass 3 mark as allowed */
	while ((name = strsep(&val, " ")) && *name) {
		ca = tcp_ca_find(name);
		WARN_ON(!ca);
		if (ca)
			ca->flags |= TCP_CONG_NON_RESTRICTED;
	}
out:
	spin_unlock(&tcp_cong_list_lock);
	kfree(saved_clone);

	return ret;
}


/* Change congestion control for socket */
int tcp_set_congestion_control(struct sock *sk, const char *name)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_congestion_ops *ca;
	int err = 0;

	rcu_read_lock();
	ca = tcp_ca_find(name);

	/* no change asking for existing value */
	if (ca == icsk->icsk_ca_ops)
		goto out;

#ifdef CONFIG_MODULES
	/* not found attempt to autoload module */
	if (!ca && capable(CAP_NET_ADMIN)) {
		rcu_read_unlock();
		request_module("tcp_%s", name);
		rcu_read_lock();
		ca = tcp_ca_find(name);
	}
#endif
	if (!ca)
		err = -ENOENT;

	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
		err = -EPERM;

	else if (!try_module_get(ca->owner))
		err = -EBUSY;

	else {
		tcp_cleanup_congestion_control(sk);
		icsk->icsk_ca_ops = ca;

		if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
			icsk->icsk_ca_ops->init(sk);
	}
 out:
	rcu_read_unlock();
	return err;
}

/* RFC2861 Check whether we are limited by application or congestion window
 * This is the inverse of cwnd check in tcp_tso_should_defer
 */
int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	u32 left;

	if (in_flight >= tp->snd_cwnd)
		return 1;

	left = tp->snd_cwnd - in_flight;
	if (sk_can_gso(sk) &&
	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
	    left * tp->mss_cache < sk->sk_gso_max_size)
		return 1;
	return left <= tcp_max_tso_deferred_mss(tp);
}
EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);

/*
 * Slow start is used when congestion window is less than slow start
 * threshold. This version implements the basic RFC2581 version
 * and optionally supports:
 * 	RFC3742 Limited Slow Start  	  - growth limited to max_ssthresh
 *	RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
 */
void tcp_slow_start(struct tcp_sock *tp)
{
	int cnt; /* increase in packets */

	/* RFC3465: ABC Slow start
	 * Increase only after a full MSS of bytes is acked
	 *
	 * TCP sender SHOULD increase cwnd by the number of
	 * previously unacknowledged bytes ACKed by each incoming
	 * acknowledgment, provided the increase is not more than L
	 */
	if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
		return;

	if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
		cnt = sysctl_tcp_max_ssthresh >> 1;	/* limited slow start */
	else
		cnt = tp->snd_cwnd;			/* exponential increase */

	/* RFC3465: ABC
	 * We MAY increase by 2 if discovered delayed ack
	 */
	if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
		cnt <<= 1;
	tp->bytes_acked = 0;

	tp->snd_cwnd_cnt += cnt;
	while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
		tp->snd_cwnd_cnt -= tp->snd_cwnd;
		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
			tp->snd_cwnd++;
	}
}
EXPORT_SYMBOL_GPL(tcp_slow_start);

/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
{
	if (tp->snd_cwnd_cnt >= w) {
		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
			tp->snd_cwnd++;
		tp->snd_cwnd_cnt = 0;
	} else {
		tp->snd_cwnd_cnt++;
	}
}
EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);

/*
 * TCP Reno congestion control
 * This is special case used for fallback as well.
 */
/* This is Jacobson's slow start and congestion avoidance.
 * SIGCOMM '88, p. 328.
 */
void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
{
	struct tcp_sock *tp = tcp_sk(sk);

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

	/* In "safe" area, increase. */
	if (tp->snd_cwnd <= tp->snd_ssthresh)
		tcp_slow_start(tp);

	/* In dangerous area, increase slowly. */
	else if (sysctl_tcp_abc) {
		/* RFC3465: Appropriate Byte Count
		 * increase once for each full cwnd acked
		 */
		if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
			tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
				tp->snd_cwnd++;
		}
	} else {
		tcp_cong_avoid_ai(tp, tp->snd_cwnd);
	}
}
EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);

/* Slow start threshold is half the congestion window (min 2) */
u32 tcp_reno_ssthresh(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	return max(tp->snd_cwnd >> 1U, 2U);
}
EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);

/* Lower bound on congestion window with halving. */
u32 tcp_reno_min_cwnd(const struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	return tp->snd_ssthresh/2;
}
EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);

struct tcp_congestion_ops tcp_reno = {
	.flags		= TCP_CONG_NON_RESTRICTED,
	.name		= "reno",
	.owner		= THIS_MODULE,
	.ssthresh	= tcp_reno_ssthresh,
	.cong_avoid	= tcp_reno_cong_avoid,
	.min_cwnd	= tcp_reno_min_cwnd,
};

/* Initial congestion control used (until SYN)
 * really reno under another name so we can tell difference
 * during tcp_set_default_congestion_control
 */
struct tcp_congestion_ops tcp_init_congestion_ops  = {
	.name		= "",
	.owner		= THIS_MODULE,
	.ssthresh	= tcp_reno_ssthresh,
	.cong_avoid	= tcp_reno_cong_avoid,
	.min_cwnd	= tcp_reno_min_cwnd,
};
EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
Commit	Line	Data
	1	/*
	2	* Plugable TCP congestion control support and newReno
	3	* congestion control.
	4	* Based on ideas from I/O scheduler suport and Web100.
	5	*
	6	* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
	7	*/
	8
	9	#include <linux/module.h>
	10	#include <linux/mm.h>
	11	#include <linux/types.h>
	12	#include <linux/list.h>
	13	#include <linux/gfp.h>
	14	#include <net/tcp.h>
	15
	16	int sysctl_tcp_max_ssthresh = 0;
	17
	18	static DEFINE_SPINLOCK(tcp_cong_list_lock);
	19	static LIST_HEAD(tcp_cong_list);
	20
	21	/* Simple linear search, don't expect many entries! */
	22	static struct tcp_congestion_ops tcp_ca_find(const char name)
	23	{
	24	struct tcp_congestion_ops *e;
	25
	26	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
	27	if (strcmp(e->name, name) == 0)
	28	return e;
	29	}
	30
	31	return NULL;
	32	}
	33
	34	/*
	35	* Attach new congestion control algorithm to the list
	36	* of available options.
	37	*/
	38	int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
	39	{
	40	int ret = 0;
	41
	42	/* all algorithms must implement ssthresh and cong_avoid ops */
	43	if (!ca->ssthresh \|\| !ca->cong_avoid) {
	44	printk(KERN_ERR "TCP %s does not implement required ops\n",
	45	ca->name);
	46	return -EINVAL;
	47	}
	48
	49	spin_lock(&tcp_cong_list_lock);
	50	if (tcp_ca_find(ca->name)) {
	51	printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
	52	ret = -EEXIST;
	53	} else {
	54	list_add_tail_rcu(&ca->list, &tcp_cong_list);
	55	printk(KERN_INFO "TCP %s registered\n", ca->name);
	56	}
	57	spin_unlock(&tcp_cong_list_lock);
	58
	59	return ret;
	60	}
	61	EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
	62
	63	/*
	64	* Remove congestion control algorithm, called from
	65	* the module's remove function. Module ref counts are used
	66	* to ensure that this can't be done till all sockets using
	67	* that method are closed.
	68	*/
	69	void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
	70	{
	71	spin_lock(&tcp_cong_list_lock);
	72	list_del_rcu(&ca->list);
	73	spin_unlock(&tcp_cong_list_lock);
	74	}
	75	EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
	76
	77	/* Assign choice of congestion control. */
	78	void tcp_init_congestion_control(struct sock *sk)
	79	{
	80	struct inet_connection_sock *icsk = inet_csk(sk);
	81	struct tcp_congestion_ops *ca;
	82
	83	/* if no choice made yet assign the current value set as default */
	84	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
	85	rcu_read_lock();
	86	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	87	if (try_module_get(ca->owner)) {
	88	icsk->icsk_ca_ops = ca;
	89	break;
	90	}
	91
	92	/* fallback to next available */
	93	}
	94	rcu_read_unlock();
	95	}
	96
	97	if (icsk->icsk_ca_ops->init)
	98	icsk->icsk_ca_ops->init(sk);
	99	}
	100
	101	/* Manage refcounts on socket close. */
	102	void tcp_cleanup_congestion_control(struct sock *sk)
	103	{
	104	struct inet_connection_sock *icsk = inet_csk(sk);
	105
	106	if (icsk->icsk_ca_ops->release)
	107	icsk->icsk_ca_ops->release(sk);
	108	module_put(icsk->icsk_ca_ops->owner);
	109	}
	110
	111	/* Used by sysctl to change default congestion control */
	112	int tcp_set_default_congestion_control(const char *name)
	113	{
	114	struct tcp_congestion_ops *ca;
	115	int ret = -ENOENT;
	116
	117	spin_lock(&tcp_cong_list_lock);
	118	ca = tcp_ca_find(name);
	119	#ifdef CONFIG_MODULES
	120	if (!ca && capable(CAP_NET_ADMIN)) {
	121	spin_unlock(&tcp_cong_list_lock);
	122
	123	request_module("tcp_%s", name);
	124	spin_lock(&tcp_cong_list_lock);
	125	ca = tcp_ca_find(name);
	126	}
	127	#endif
	128
	129	if (ca) {
	130	ca->flags \|= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
	131	list_move(&ca->list, &tcp_cong_list);
	132	ret = 0;
	133	}
	134	spin_unlock(&tcp_cong_list_lock);
	135
	136	return ret;
	137	}
	138
	139	/* Set default value from kernel configuration at bootup */
	140	static int __init tcp_congestion_default(void)
	141	{
	142	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
	143	}
	144	late_initcall(tcp_congestion_default);
	145
	146
	147	/* Build string with list of available congestion control values */
	148	void tcp_get_available_congestion_control(char *buf, size_t maxlen)
	149	{
	150	struct tcp_congestion_ops *ca;
	151	size_t offs = 0;
	152
	153	rcu_read_lock();
	154	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	155	offs += snprintf(buf + offs, maxlen - offs,
	156	"%s%s",
	157	offs == 0 ? "" : " ", ca->name);
	158
	159	}
	160	rcu_read_unlock();
	161	}
	162
	163	/* Get current default congestion control */
	164	void tcp_get_default_congestion_control(char *name)
	165	{
	166	struct tcp_congestion_ops *ca;
	167	/* We will always have reno... */
	168	BUG_ON(list_empty(&tcp_cong_list));
	169
	170	rcu_read_lock();
	171	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	172	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	173	rcu_read_unlock();
	174	}
	175
	176	/* Built list of non-restricted congestion control values */
	177	void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
	178	{
	179	struct tcp_congestion_ops *ca;
	180	size_t offs = 0;
	181
	182	*buf = '\0';
	183	rcu_read_lock();
	184	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	185	if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
	186	continue;
	187	offs += snprintf(buf + offs, maxlen - offs,
	188	"%s%s",
	189	offs == 0 ? "" : " ", ca->name);
	190
	191	}
	192	rcu_read_unlock();
	193	}
	194
	195	/* Change list of non-restricted congestion control */
	196	int tcp_set_allowed_congestion_control(char *val)
	197	{
	198	struct tcp_congestion_ops *ca;
	199	char saved_clone, clone, *name;
	200	int ret = 0;
	201
	202	saved_clone = clone = kstrdup(val, GFP_USER);
	203	if (!clone)
	204	return -ENOMEM;
	205
	206	spin_lock(&tcp_cong_list_lock);
	207	/* pass 1 check for bad entries */
	208	while ((name = strsep(&clone, " ")) && *name) {
	209	ca = tcp_ca_find(name);
	210	if (!ca) {
	211	ret = -ENOENT;
	212	goto out;
	213	}
	214	}
	215
	216	/* pass 2 clear old values */
	217	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
	218	ca->flags &= ~TCP_CONG_NON_RESTRICTED;
	219
	220	/* pass 3 mark as allowed */
	221	while ((name = strsep(&val, " ")) && *name) {
	222	ca = tcp_ca_find(name);
	223	WARN_ON(!ca);
	224	if (ca)
	225	ca->flags \|= TCP_CONG_NON_RESTRICTED;
	226	}
	227	out:
	228	spin_unlock(&tcp_cong_list_lock);
	229	kfree(saved_clone);
	230
	231	return ret;
	232	}
	233
	234
	235	/* Change congestion control for socket */
	236	int tcp_set_congestion_control(struct sock sk, const char name)
	237	{
	238	struct inet_connection_sock *icsk = inet_csk(sk);
	239	struct tcp_congestion_ops *ca;
	240	int err = 0;
	241
	242	rcu_read_lock();
	243	ca = tcp_ca_find(name);
	244
	245	/* no change asking for existing value */
	246	if (ca == icsk->icsk_ca_ops)
	247	goto out;
	248
	249	#ifdef CONFIG_MODULES
	250	/* not found attempt to autoload module */
	251	if (!ca && capable(CAP_NET_ADMIN)) {
	252	rcu_read_unlock();
	253	request_module("tcp_%s", name);
	254	rcu_read_lock();
	255	ca = tcp_ca_find(name);
	256	}
	257	#endif
	258	if (!ca)
	259	err = -ENOENT;
	260
	261	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) \|\| capable(CAP_NET_ADMIN)))
	262	err = -EPERM;
	263
	264	else if (!try_module_get(ca->owner))
	265	err = -EBUSY;
	266
	267	else {
	268	tcp_cleanup_congestion_control(sk);
	269	icsk->icsk_ca_ops = ca;
	270
	271	if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
	272	icsk->icsk_ca_ops->init(sk);
	273	}
	274	out:
	275	rcu_read_unlock();
	276	return err;
	277	}
	278
	279	/* RFC2861 Check whether we are limited by application or congestion window
	280	* This is the inverse of cwnd check in tcp_tso_should_defer
	281	*/
	282	int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
	283	{
	284	const struct tcp_sock *tp = tcp_sk(sk);
	285	u32 left;
	286
	287	if (in_flight >= tp->snd_cwnd)
	288	return 1;
	289
	290	left = tp->snd_cwnd - in_flight;
	291	if (sk_can_gso(sk) &&
	292	left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
	293	left * tp->mss_cache < sk->sk_gso_max_size)
	294	return 1;
	295	return left <= tcp_max_tso_deferred_mss(tp);
	296	}
	297	EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
	298
	299	/*
	300	* Slow start is used when congestion window is less than slow start
	301	* threshold. This version implements the basic RFC2581 version
	302	* and optionally supports:
	303	* RFC3742 Limited Slow Start - growth limited to max_ssthresh
	304	* RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
	305	*/
	306	void tcp_slow_start(struct tcp_sock *tp)
	307	{
	308	int cnt; /* increase in packets */
	309
	310	/* RFC3465: ABC Slow start
	311	* Increase only after a full MSS of bytes is acked
	312	*
	313	* TCP sender SHOULD increase cwnd by the number of
	314	* previously unacknowledged bytes ACKed by each incoming
	315	* acknowledgment, provided the increase is not more than L
	316	*/
	317	if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
	318	return;
	319
	320	if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
	321	cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
	322	else
	323	cnt = tp->snd_cwnd; /* exponential increase */
	324
	325	/* RFC3465: ABC
	326	* We MAY increase by 2 if discovered delayed ack
	327	*/
	328	if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
	329	cnt <<= 1;
	330	tp->bytes_acked = 0;
	331
	332	tp->snd_cwnd_cnt += cnt;
	333	while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
	334	tp->snd_cwnd_cnt -= tp->snd_cwnd;
	335	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	336	tp->snd_cwnd++;
	337	}
	338	}
	339	EXPORT_SYMBOL_GPL(tcp_slow_start);
	340
	341	/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
	342	void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
	343	{
	344	if (tp->snd_cwnd_cnt >= w) {
	345	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	346	tp->snd_cwnd++;
	347	tp->snd_cwnd_cnt = 0;
	348	} else {
	349	tp->snd_cwnd_cnt++;
	350	}
	351	}
	352	EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
	353
	354	/*
	355	* TCP Reno congestion control
	356	* This is special case used for fallback as well.
	357	*/
	358	/* This is Jacobson's slow start and congestion avoidance.
	359	* SIGCOMM '88, p. 328.
	360	*/
	361	void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
	362	{
	363	struct tcp_sock *tp = tcp_sk(sk);
	364
	365	if (!tcp_is_cwnd_limited(sk, in_flight))
	366	return;
	367
	368	/* In "safe" area, increase. */
	369	if (tp->snd_cwnd <= tp->snd_ssthresh)
	370	tcp_slow_start(tp);
	371
	372	/* In dangerous area, increase slowly. */
	373	else if (sysctl_tcp_abc) {
	374	/* RFC3465: Appropriate Byte Count
	375	* increase once for each full cwnd acked
	376	*/
	377	if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
	378	tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
	379	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	380	tp->snd_cwnd++;
	381	}
	382	} else {
	383	tcp_cong_avoid_ai(tp, tp->snd_cwnd);
	384	}
	385	}
	386	EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
	387
	388	/* Slow start threshold is half the congestion window (min 2) */
	389	u32 tcp_reno_ssthresh(struct sock *sk)
	390	{
	391	const struct tcp_sock *tp = tcp_sk(sk);
	392	return max(tp->snd_cwnd >> 1U, 2U);
	393	}
	394	EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
	395
	396	/* Lower bound on congestion window with halving. */
	397	u32 tcp_reno_min_cwnd(const struct sock *sk)
	398	{
	399	const struct tcp_sock *tp = tcp_sk(sk);
	400	return tp->snd_ssthresh/2;
	401	}
	402	EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
	403
	404	struct tcp_congestion_ops tcp_reno = {
	405	.flags = TCP_CONG_NON_RESTRICTED,
	406	.name = "reno",
	407	.owner = THIS_MODULE,
	408	.ssthresh = tcp_reno_ssthresh,
	409	.cong_avoid = tcp_reno_cong_avoid,
	410	.min_cwnd = tcp_reno_min_cwnd,
	411	};
	412
	413	/* Initial congestion control used (until SYN)
	414	* really reno under another name so we can tell difference
	415	* during tcp_set_default_congestion_control
	416	*/
	417	struct tcp_congestion_ops tcp_init_congestion_ops = {
	418	.name = "",
	419	.owner = THIS_MODULE,
	420	.ssthresh = tcp_reno_ssthresh,
	421	.cong_avoid = tcp_reno_cong_avoid,
	422	.min_cwnd = tcp_reno_min_cwnd,
	423	};
	424	EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);