[mirror_ubuntu-artful-kernel.git] / net / ipv4 / tcp_cong.c

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

#define pr_fmt(fmt) "TCP: " fmt

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

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) {
		pr_err("%s does not implement required ops\n", ca->name);
		return -EINVAL;
	}

	spin_lock(&tcp_cong_list_lock);
	if (tcp_ca_find(ca->name)) {
		pr_notice("%s already registered\n", ca->name);
		ret = -EEXIST;
	} else {
		list_add_tail_rcu(&ca->list, &tcp_cong_list);
		pr_info("%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_assign_congestion_control(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_congestion_ops *ca;

	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
		if (likely(try_module_get(ca->owner))) {
			icsk->icsk_ca_ops = ca;
			goto out;
		}
		/* Fallback to next available. The last really
		 * guaranteed fallback is Reno from this list.
		 */
	}
out:
	rcu_read_unlock();

	/* Clear out private data before diag gets it and
	 * the ca has not been initialized.
	 */
	if (ca->get_info)
		memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
}

void tcp_init_congestion_control(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);

	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) ||
		   ns_capable(sock_net(sk)->user_ns, 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;
}

/* Slow start is used when congestion window is no greater than the slow start
 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 * something better;) a packet is only considered (s)acked in its entirety to
 * defend the ACK attacks described in the RFC. Slow start processes a stretch
 * ACK of degree N as if N acks of degree 1 are received back to back except
 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 */
void tcp_slow_start(struct tcp_sock *tp, u32 acked)
{
	u32 cwnd = tp->snd_cwnd + acked;

	if (cwnd > tp->snd_ssthresh)
		cwnd = tp->snd_ssthresh + 1;
	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
}
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 acked)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (!tcp_is_cwnd_limited(sk))
		return;

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

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,
};
Commit	Line	Data
317a76f9	1	/*
b92022f3	2	* Pluggable TCP congestion control support and newReno
317a76f9	3	* congestion control.
02582e9b	4	* Based on ideas from I/O scheduler support and Web100.
317a76f9 SH	5	*
	6	* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
	7	*/
	8
afd46503 JP	9	#define pr_fmt(fmt) "TCP: " fmt
afd46503 JP	10
317a76f9 SH	11	#include <linux/module.h>
	12	#include <linux/mm.h>
	13	#include <linux/types.h>
	14	#include <linux/list.h>
5a0e3ad6	15	#include <linux/gfp.h>
317a76f9 SH	16	#include <net/tcp.h>
	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
5f8ef48d	26	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
317a76f9 SH	27	if (strcmp(e->name, name) == 0)
	28	return e;
	29	}
	30
	31	return NULL;
	32	}
	33
	34	/*
d08df601	35	* Attach new congestion control algorithm to the list
317a76f9 SH	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 */
72dc5b92	43	if (!ca->ssthresh \|\| !ca->cong_avoid) {
afd46503	44	pr_err("%s does not implement required ops\n", ca->name);
317a76f9 SH	45	return -EINVAL;
	46	}
	47
	48	spin_lock(&tcp_cong_list_lock);
	49	if (tcp_ca_find(ca->name)) {
afd46503	50	pr_notice("%s already registered\n", ca->name);
317a76f9 SH	51	ret = -EEXIST;
317a76f9 SH	52	} else {
3d2573f7	53	list_add_tail_rcu(&ca->list, &tcp_cong_list);
afd46503	54	pr_info("%s registered\n", ca->name);
317a76f9 SH	55	}
	56	spin_unlock(&tcp_cong_list_lock);
	57
	58	return ret;
	59	}
	60	EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
	61
	62	/*
	63	* Remove congestion control algorithm, called from
	64	* the module's remove function. Module ref counts are used
	65	* to ensure that this can't be done till all sockets using
	66	* that method are closed.
	67	*/
	68	void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
	69	{
	70	spin_lock(&tcp_cong_list_lock);
	71	list_del_rcu(&ca->list);
	72	spin_unlock(&tcp_cong_list_lock);
	73	}
	74	EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
	75
	76	/* Assign choice of congestion control. */
55d8694f	77	void tcp_assign_congestion_control(struct sock *sk)
317a76f9	78	{
6687e988	79	struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9 SH	80	struct tcp_congestion_ops *ca;
317a76f9 SH	81
55d8694f FW	82	rcu_read_lock();
	83	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	84	if (likely(try_module_get(ca->owner))) {
	85	icsk->icsk_ca_ops = ca;
	86	goto out;
317a76f9	87	}
55d8694f FW	88	/* Fallback to next available. The last really
	89	* guaranteed fallback is Reno from this list.
	90	*/
317a76f9	91	}
55d8694f FW	92	out:
	93	rcu_read_unlock();
	94
	95	/* Clear out private data before diag gets it and
	96	* the ca has not been initialized.
	97	*/
	98	if (ca->get_info)
	99	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
	100	}
	101
	102	void tcp_init_congestion_control(struct sock *sk)
	103	{
	104	const struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9	105
6687e988 ACM	106	if (icsk->icsk_ca_ops->init)
6687e988 ACM	107	icsk->icsk_ca_ops->init(sk);
317a76f9 SH	108	}
	109
	110	/* Manage refcounts on socket close. */
6687e988	111	void tcp_cleanup_congestion_control(struct sock *sk)
317a76f9	112	{
6687e988 ACM	113	struct inet_connection_sock *icsk = inet_csk(sk);
	114
	115	if (icsk->icsk_ca_ops->release)
	116	icsk->icsk_ca_ops->release(sk);
	117	module_put(icsk->icsk_ca_ops->owner);
317a76f9 SH	118	}
	119
	120	/* Used by sysctl to change default congestion control */
	121	int tcp_set_default_congestion_control(const char *name)
	122	{
	123	struct tcp_congestion_ops *ca;
	124	int ret = -ENOENT;
	125
	126	spin_lock(&tcp_cong_list_lock);
	127	ca = tcp_ca_find(name);
95a5afca	128	#ifdef CONFIG_MODULES
a8f80e8f	129	if (!ca && capable(CAP_NET_ADMIN)) {
317a76f9 SH	130	spin_unlock(&tcp_cong_list_lock);
	131
	132	request_module("tcp_%s", name);
	133	spin_lock(&tcp_cong_list_lock);
	134	ca = tcp_ca_find(name);
	135	}
	136	#endif
	137
	138	if (ca) {
164891aa	139	ca->flags \|= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
317a76f9 SH	140	list_move(&ca->list, &tcp_cong_list);
	141	ret = 0;
	142	}
	143	spin_unlock(&tcp_cong_list_lock);
	144
	145	return ret;
	146	}
	147
b1736a71 SH	148	/* Set default value from kernel configuration at bootup */
	149	static int __init tcp_congestion_default(void)
	150	{
	151	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
	152	}
	153	late_initcall(tcp_congestion_default);
	154
3ff825b2 SH	155	/* Build string with list of available congestion control values */
	156	void tcp_get_available_congestion_control(char *buf, size_t maxlen)
	157	{
	158	struct tcp_congestion_ops *ca;
	159	size_t offs = 0;
	160
	161	rcu_read_lock();
	162	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	163	offs += snprintf(buf + offs, maxlen - offs,
	164	"%s%s",
	165	offs == 0 ? "" : " ", ca->name);
3ff825b2 SH	166	}
	167	rcu_read_unlock();
	168	}
	169
317a76f9 SH	170	/* Get current default congestion control */
	171	void tcp_get_default_congestion_control(char *name)
	172	{
	173	struct tcp_congestion_ops *ca;
	174	/* We will always have reno... */
	175	BUG_ON(list_empty(&tcp_cong_list));
	176
	177	rcu_read_lock();
	178	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	179	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	180	rcu_read_unlock();
	181	}
	182
ce7bc3bf SH	183	/* Built list of non-restricted congestion control values */
	184	void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
	185	{
	186	struct tcp_congestion_ops *ca;
	187	size_t offs = 0;
	188
	189	*buf = '\0';
	190	rcu_read_lock();
	191	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
164891aa	192	if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
ce7bc3bf SH	193	continue;
	194	offs += snprintf(buf + offs, maxlen - offs,
	195	"%s%s",
	196	offs == 0 ? "" : " ", ca->name);
ce7bc3bf SH	197	}
	198	rcu_read_unlock();
	199	}
	200
	201	/* Change list of non-restricted congestion control */
	202	int tcp_set_allowed_congestion_control(char *val)
	203	{
	204	struct tcp_congestion_ops *ca;
c34186ed	205	char saved_clone, clone, *name;
ce7bc3bf SH	206	int ret = 0;
ce7bc3bf SH	207
c34186ed	208	saved_clone = clone = kstrdup(val, GFP_USER);
ce7bc3bf SH	209	if (!clone)
	210	return -ENOMEM;
	211
	212	spin_lock(&tcp_cong_list_lock);
	213	/* pass 1 check for bad entries */
	214	while ((name = strsep(&clone, " ")) && *name) {
	215	ca = tcp_ca_find(name);
	216	if (!ca) {
	217	ret = -ENOENT;
	218	goto out;
	219	}
	220	}
	221
164891aa	222	/* pass 2 clear old values */
ce7bc3bf	223	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
164891aa	224	ca->flags &= ~TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	225
	226	/* pass 3 mark as allowed */
	227	while ((name = strsep(&val, " ")) && *name) {
	228	ca = tcp_ca_find(name);
	229	WARN_ON(!ca);
	230	if (ca)
164891aa	231	ca->flags \|= TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	232	}
	233	out:
	234	spin_unlock(&tcp_cong_list_lock);
c34186ed	235	kfree(saved_clone);
ce7bc3bf SH	236
	237	return ret;
	238	}
	239
5f8ef48d	240	/* Change congestion control for socket */
6687e988	241	int tcp_set_congestion_control(struct sock sk, const char name)
5f8ef48d	242	{
6687e988	243	struct inet_connection_sock *icsk = inet_csk(sk);
5f8ef48d SH	244	struct tcp_congestion_ops *ca;
	245	int err = 0;
	246
	247	rcu_read_lock();
	248	ca = tcp_ca_find(name);
4d4d3d1e	249
35bfbc94	250	/* no change asking for existing value */
6687e988	251	if (ca == icsk->icsk_ca_ops)
5f8ef48d SH	252	goto out;
5f8ef48d SH	253
95a5afca	254	#ifdef CONFIG_MODULES
35bfbc94	255	/* not found attempt to autoload module */
a8f80e8f	256	if (!ca && capable(CAP_NET_ADMIN)) {
35bfbc94 SH	257	rcu_read_unlock();
	258	request_module("tcp_%s", name);
	259	rcu_read_lock();
	260	ca = tcp_ca_find(name);
	261	}
	262	#endif
5f8ef48d SH	263	if (!ca)
	264	err = -ENOENT;
	265
52e804c6 EB	266	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) \|\|
52e804c6 EB	267	ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
ce7bc3bf SH	268	err = -EPERM;
ce7bc3bf SH	269
5f8ef48d SH	270	else if (!try_module_get(ca->owner))
	271	err = -EBUSY;
	272
	273	else {
6687e988 ACM	274	tcp_cleanup_congestion_control(sk);
6687e988 ACM	275	icsk->icsk_ca_ops = ca;
4d4d3d1e SH	276
4d4d3d1e SH	277	if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
6687e988	278	icsk->icsk_ca_ops->init(sk);
5f8ef48d SH	279	}
	280	out:
	281	rcu_read_unlock();
	282	return err;
	283	}
	284
9f9843a7 YC	285	/* Slow start is used when congestion window is no greater than the slow start
	286	* threshold. We base on RFC2581 and also handle stretch ACKs properly.
	287	* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
	288	* something better;) a packet is only considered (s)acked in its entirety to
	289	* defend the ACK attacks described in the RFC. Slow start processes a stretch
	290	* ACK of degree N as if N acks of degree 1 are received back to back except
	291	* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
	292	* returns the leftover acks to adjust cwnd in congestion avoidance mode.
40efc6fa	293	*/
a12a601e	294	void tcp_slow_start(struct tcp_sock *tp, u32 acked)
40efc6fa	295	{
9f9843a7	296	u32 cwnd = tp->snd_cwnd + acked;
a02ba041	297
9f9843a7 YC	298	if (cwnd > tp->snd_ssthresh)
9f9843a7 YC	299	cwnd = tp->snd_ssthresh + 1;
9f9843a7	300	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
40efc6fa SH	301	}
	302	EXPORT_SYMBOL_GPL(tcp_slow_start);
	303
758ce5c8 IJ	304	/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
	305	void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
	306	{
	307	if (tp->snd_cwnd_cnt >= w) {
	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	EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
	316
317a76f9 SH	317	/*
	318	* TCP Reno congestion control
	319	* This is special case used for fallback as well.
	320	*/
	321	/* This is Jacobson's slow start and congestion avoidance.
	322	* SIGCOMM '88, p. 328.
	323	*/
24901551	324	void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
317a76f9	325	{
6687e988 ACM	326	struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	327
24901551	328	if (!tcp_is_cwnd_limited(sk))
317a76f9 SH	329	return;
317a76f9 SH	330
7faffa1c	331	/* In "safe" area, increase. */
e905a9ed	332	if (tp->snd_cwnd <= tp->snd_ssthresh)
9f9843a7	333	tcp_slow_start(tp, acked);
e905a9ed	334	/* In dangerous area, increase slowly. */
ca2eb567	335	else
758ce5c8	336	tcp_cong_avoid_ai(tp, tp->snd_cwnd);
317a76f9 SH	337	}
	338	EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
	339
	340	/* Slow start threshold is half the congestion window (min 2) */
6687e988	341	u32 tcp_reno_ssthresh(struct sock *sk)
317a76f9	342	{
6687e988	343	const struct tcp_sock *tp = tcp_sk(sk);
688d1945	344
317a76f9 SH	345	return max(tp->snd_cwnd >> 1U, 2U);
	346	}
	347	EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
	348
317a76f9	349	struct tcp_congestion_ops tcp_reno = {
164891aa	350	.flags = TCP_CONG_NON_RESTRICTED,
317a76f9 SH	351	.name = "reno",
	352	.owner = THIS_MODULE,
	353	.ssthresh = tcp_reno_ssthresh,
	354	.cong_avoid = tcp_reno_cong_avoid,
317a76f9	355	};