[deliverable/linux.git] / net / ipv4 / tcp_vegas.c

/*
 * TCP Vegas congestion control
 *
 * This is based on the congestion detection/avoidance scheme described in
 *    Lawrence S. Brakmo and Larry L. Peterson.
 *    "TCP Vegas: End to end congestion avoidance on a global internet."
 *    IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
 *    October 1995. Available from:
 *	ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
 *
 * See http://www.cs.arizona.edu/xkernel/ for their implementation.
 * The main aspects that distinguish this implementation from the
 * Arizona Vegas implementation are:
 *   o We do not change the loss detection or recovery mechanisms of
 *     Linux in any way. Linux already recovers from losses quite well,
 *     using fine-grained timers, NewReno, and FACK.
 *   o To avoid the performance penalty imposed by increasing cwnd
 *     only every-other RTT during slow start, we increase during
 *     every RTT during slow start, just like Reno.
 *   o Largely to allow continuous cwnd growth during slow start,
 *     we use the rate at which ACKs come back as the "actual"
 *     rate, rather than the rate at which data is sent.
 *   o To speed convergence to the right rate, we set the cwnd
 *     to achieve the right ("actual") rate when we exit slow start.
 *   o To filter out the noise caused by delayed ACKs, we use the
 *     minimum RTT sample observed during the last RTT to calculate
 *     the actual rate.
 *   o When the sender re-starts from idle, it waits until it has
 *     received ACKs for an entire flight of new data before making
 *     a cwnd adjustment decision. The original Vegas implementation
 *     assumed senders never went idle.
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>

#include <net/tcp.h>

#include "tcp_vegas.h"

/* Default values of the Vegas variables, in fixed-point representation
 * with V_PARAM_SHIFT bits to the right of the binary point.
 */
#define V_PARAM_SHIFT 1
static int alpha = 2<<V_PARAM_SHIFT;
static int beta  = 4<<V_PARAM_SHIFT;
static int gamma = 1<<V_PARAM_SHIFT;

module_param(alpha, int, 0644);
MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");
module_param(beta, int, 0644);
MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");
module_param(gamma, int, 0644);
MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");


/* There are several situations when we must "re-start" Vegas:
 *
 *  o when a connection is established
 *  o after an RTO
 *  o after fast recovery
 *  o when we send a packet and there is no outstanding
 *    unacknowledged data (restarting an idle connection)
 *
 * In these circumstances we cannot do a Vegas calculation at the
 * end of the first RTT, because any calculation we do is using
 * stale info -- both the saved cwnd and congestion feedback are
 * stale.
 *
 * Instead we must wait until the completion of an RTT during
 * which we actually receive ACKs.
 */
static void vegas_enable(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct vegas *vegas = inet_csk_ca(sk);

	/* Begin taking Vegas samples next time we send something. */
	vegas->doing_vegas_now = 1;

	/* Set the beginning of the next send window. */
	vegas->beg_snd_nxt = tp->snd_nxt;

	vegas->cntRTT = 0;
	vegas->minRTT = 0x7fffffff;
}

/* Stop taking Vegas samples for now. */
static inline void vegas_disable(struct sock *sk)
{
	struct vegas *vegas = inet_csk_ca(sk);

	vegas->doing_vegas_now = 0;
}

void tcp_vegas_init(struct sock *sk)
{
	struct vegas *vegas = inet_csk_ca(sk);

	vegas->baseRTT = 0x7fffffff;
	vegas_enable(sk);
}
EXPORT_SYMBOL_GPL(tcp_vegas_init);

/* Do RTT sampling needed for Vegas.
 * Basically we:
 *   o min-filter RTT samples from within an RTT to get the current
 *     propagation delay + queuing delay (we are min-filtering to try to
 *     avoid the effects of delayed ACKs)
 *   o min-filter RTT samples from a much longer window (forever for now)
 *     to find the propagation delay (baseRTT)
 */
void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
{
	struct vegas *vegas = inet_csk_ca(sk);
	u32 vrtt;

	if (rtt_us < 0)
		return;

	/* Never allow zero rtt or baseRTT */
	vrtt = rtt_us + 1;

	/* Filter to find propagation delay: */
	if (vrtt < vegas->baseRTT)
		vegas->baseRTT = vrtt;

	/* Find the min RTT during the last RTT to find
	 * the current prop. delay + queuing delay:
	 */
	vegas->minRTT = min(vegas->minRTT, vrtt);
	vegas->cntRTT++;
}
EXPORT_SYMBOL_GPL(tcp_vegas_pkts_acked);

void tcp_vegas_state(struct sock *sk, u8 ca_state)
{

	if (ca_state == TCP_CA_Open)
		vegas_enable(sk);
	else
		vegas_disable(sk);
}
EXPORT_SYMBOL_GPL(tcp_vegas_state);

/*
 * If the connection is idle and we are restarting,
 * then we don't want to do any Vegas calculations
 * until we get fresh RTT samples.  So when we
 * restart, we reset our Vegas state to a clean
 * slate. After we get acks for this flight of
 * packets, _then_ we can make Vegas calculations
 * again.
 */
void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
	if (event == CA_EVENT_CWND_RESTART ||
	    event == CA_EVENT_TX_START)
		tcp_vegas_init(sk);
}
EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);

static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct vegas *vegas = inet_csk_ca(sk);

	if (!vegas->doing_vegas_now)
		return tcp_reno_cong_avoid(sk, ack, in_flight);

	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
	 *
	 * These are so named because they represent the approximate values
	 * of snd_una and snd_nxt at the beginning of the current RTT. More
	 * precisely, they represent the amount of data sent during the RTT.
	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
	 * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
	 * bytes of data have been ACKed during the course of the RTT, giving
	 * an "actual" rate of:
	 *
	 *     (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
	 *
	 * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
	 * because delayed ACKs can cover more than one segment, so they
	 * don't line up nicely with the boundaries of RTTs.
	 *
	 * Another unfortunate fact of life is that delayed ACKs delay the
	 * advance of the left edge of our send window, so that the number
	 * of bytes we send in an RTT is often less than our cwnd will allow.
	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
	 */

	if (after(ack, vegas->beg_snd_nxt)) {
		/* Do the Vegas once-per-RTT cwnd adjustment. */
		u32 old_wnd, old_snd_cwnd;


		/* Here old_wnd is essentially the window of data that was
		 * sent during the previous RTT, and has all
		 * been acknowledged in the course of the RTT that ended
		 * with the ACK we just received. Likewise, old_snd_cwnd
		 * is the cwnd during the previous RTT.
		 */
		old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
			tp->mss_cache;
		old_snd_cwnd = vegas->beg_snd_cwnd;

		/* Save the extent of the current window so we can use this
		 * at the end of the next RTT.
		 */
		vegas->beg_snd_una  = vegas->beg_snd_nxt;
		vegas->beg_snd_nxt  = tp->snd_nxt;
		vegas->beg_snd_cwnd = tp->snd_cwnd;

		/* We do the Vegas calculations only if we got enough RTT
		 * samples that we can be reasonably sure that we got
		 * at least one RTT sample that wasn't from a delayed ACK.
		 * If we only had 2 samples total,
		 * then that means we're getting only 1 ACK per RTT, which
		 * means they're almost certainly delayed ACKs.
		 * If  we have 3 samples, we should be OK.
		 */

		if (vegas->cntRTT <= 2) {
			/* We don't have enough RTT samples to do the Vegas
			 * calculation, so we'll behave like Reno.
			 */
			tcp_reno_cong_avoid(sk, ack, in_flight);
		} else {
			u32 rtt, diff;
			u64 target_cwnd;

			/* We have enough RTT samples, so, using the Vegas
			 * algorithm, we determine if we should increase or
			 * decrease cwnd, and by how much.
			 */

			/* Pluck out the RTT we are using for the Vegas
			 * calculations. This is the min RTT seen during the
			 * last RTT. Taking the min filters out the effects
			 * of delayed ACKs, at the cost of noticing congestion
			 * a bit later.
			 */
			rtt = vegas->minRTT;

			/* Calculate the cwnd we should have, if we weren't
			 * going too fast.
			 *
			 * This is:
			 *     (actual rate in segments) * baseRTT
			 * We keep it as a fixed point number with
			 * V_PARAM_SHIFT bits to the right of the binary point.
			 */
			target_cwnd = ((u64)old_wnd * vegas->baseRTT);
			target_cwnd <<= V_PARAM_SHIFT;
			do_div(target_cwnd, rtt);

			/* Calculate the difference between the window we had,
			 * and the window we would like to have. This quantity
			 * is the "Diff" from the Arizona Vegas papers.
			 *
			 * Again, this is a fixed point number with
			 * V_PARAM_SHIFT bits to the right of the binary
			 * point.
			 */
			diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;

			if (diff > gamma && tp->snd_ssthresh > 2 ) {
				/* Going too fast. Time to slow down
				 * and switch to congestion avoidance.
				 */
				tp->snd_ssthresh = 2;

				/* Set cwnd to match the actual rate
				 * exactly:
				 *   cwnd = (actual rate) * baseRTT
				 * Then we add 1 because the integer
				 * truncation robs us of full link
				 * utilization.
				 */
				tp->snd_cwnd = min(tp->snd_cwnd,
						   ((u32)target_cwnd >>
						    V_PARAM_SHIFT)+1);

			} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
				/* Slow start.  */
				tcp_slow_start(tp);
			} else {
				/* Congestion avoidance. */
				u32 next_snd_cwnd;

				/* Figure out where we would like cwnd
				 * to be.
				 */
				if (diff > beta) {
					/* The old window was too fast, so
					 * we slow down.
					 */
					next_snd_cwnd = old_snd_cwnd - 1;
				} else if (diff < alpha) {
					/* We don't have enough extra packets
					 * in the network, so speed up.
					 */
					next_snd_cwnd = old_snd_cwnd + 1;
				} else {
					/* Sending just as fast as we
					 * should be.
					 */
					next_snd_cwnd = old_snd_cwnd;
				}

				/* Adjust cwnd upward or downward, toward the
				 * desired value.
				 */
				if (next_snd_cwnd > tp->snd_cwnd)
					tp->snd_cwnd++;
				else if (next_snd_cwnd < tp->snd_cwnd)
					tp->snd_cwnd--;
			}

			if (tp->snd_cwnd < 2)
				tp->snd_cwnd = 2;
			else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
				tp->snd_cwnd = tp->snd_cwnd_clamp;
		}

		/* Wipe the slate clean for the next RTT. */
		vegas->cntRTT = 0;
		vegas->minRTT = 0x7fffffff;
	}
	/* Use normal slow start */
	else if (tp->snd_cwnd <= tp->snd_ssthresh)
		tcp_slow_start(tp);

}

/* Extract info for Tcp socket info provided via netlink. */
void tcp_vegas_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
{
	const struct vegas *ca = inet_csk_ca(sk);
	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
		struct tcpvegas_info info = {
			.tcpv_enabled = ca->doing_vegas_now,
			.tcpv_rttcnt = ca->cntRTT,
			.tcpv_rtt = ca->baseRTT,
			.tcpv_minrtt = ca->minRTT,
		};

		nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
	}
}
EXPORT_SYMBOL_GPL(tcp_vegas_get_info);

static struct tcp_congestion_ops tcp_vegas = {
	.flags		= TCP_CONG_RTT_STAMP,
	.init		= tcp_vegas_init,
	.ssthresh	= tcp_reno_ssthresh,
	.cong_avoid	= tcp_vegas_cong_avoid,
	.min_cwnd	= tcp_reno_min_cwnd,
	.pkts_acked	= tcp_vegas_pkts_acked,
	.set_state	= tcp_vegas_state,
	.cwnd_event	= tcp_vegas_cwnd_event,
	.get_info	= tcp_vegas_get_info,

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

static int __init tcp_vegas_register(void)
{
	BUILD_BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE);
	tcp_register_congestion_control(&tcp_vegas);
	return 0;
}

static void __exit tcp_vegas_unregister(void)
{
	tcp_unregister_congestion_control(&tcp_vegas);
}

module_init(tcp_vegas_register);
module_exit(tcp_vegas_unregister);

MODULE_AUTHOR("Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Vegas");
Commit	Line	Data
b87d8561 SH	1	/*
	2	* TCP Vegas congestion control
	3	*
	4	* This is based on the congestion detection/avoidance scheme described in
	5	* Lawrence S. Brakmo and Larry L. Peterson.
	6	* "TCP Vegas: End to end congestion avoidance on a global internet."
	7	* IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
	8	* October 1995. Available from:
	9	* ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
	10	*
	11	* See http://www.cs.arizona.edu/xkernel/ for their implementation.
	12	* The main aspects that distinguish this implementation from the
	13	* Arizona Vegas implementation are:
	14	* o We do not change the loss detection or recovery mechanisms of
	15	* Linux in any way. Linux already recovers from losses quite well,
	16	* using fine-grained timers, NewReno, and FACK.
	17	* o To avoid the performance penalty imposed by increasing cwnd
	18	* only every-other RTT during slow start, we increase during
	19	* every RTT during slow start, just like Reno.
	20	* o Largely to allow continuous cwnd growth during slow start,
	21	* we use the rate at which ACKs come back as the "actual"
	22	* rate, rather than the rate at which data is sent.
	23	* o To speed convergence to the right rate, we set the cwnd
	24	* to achieve the right ("actual") rate when we exit slow start.
	25	* o To filter out the noise caused by delayed ACKs, we use the
	26	* minimum RTT sample observed during the last RTT to calculate
	27	* the actual rate.
	28	* o When the sender re-starts from idle, it waits until it has
	29	* received ACKs for an entire flight of new data before making
	30	* a cwnd adjustment decision. The original Vegas implementation
	31	* assumed senders never went idle.
	32	*/
	33
b87d8561 SH	34	#include <linux/mm.h>
	35	#include <linux/module.h>
	36	#include <linux/skbuff.h>
a8c2190e	37	#include <linux/inet_diag.h>
b87d8561 SH	38
	39	#include <net/tcp.h>
	40
7752237e SH	41	#include "tcp_vegas.h"
7752237e SH	42
b87d8561 SH	43	/* Default values of the Vegas variables, in fixed-point representation
	44	* with V_PARAM_SHIFT bits to the right of the binary point.
	45	*/
	46	#define V_PARAM_SHIFT 1
d2e4bdc8 DM	47	static int alpha = 2<<V_PARAM_SHIFT;
d2e4bdc8 DM	48	static int beta = 4<<V_PARAM_SHIFT;
b87d8561 SH	49	static int gamma = 1<<V_PARAM_SHIFT;
	50
	51	module_param(alpha, int, 0644);
	52	MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");
	53	module_param(beta, int, 0644);
	54	MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");
	55	module_param(gamma, int, 0644);
	56	MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");
	57
	58
b87d8561 SH	59	/* There are several situations when we must "re-start" Vegas:
	60	*
	61	* o when a connection is established
	62	* o after an RTO
	63	* o after fast recovery
	64	* o when we send a packet and there is no outstanding
	65	* unacknowledged data (restarting an idle connection)
	66	*
	67	* In these circumstances we cannot do a Vegas calculation at the
	68	* end of the first RTT, because any calculation we do is using
	69	* stale info -- both the saved cwnd and congestion feedback are
	70	* stale.
	71	*
	72	* Instead we must wait until the completion of an RTT during
	73	* which we actually receive ACKs.
	74	*/
7752237e	75	static void vegas_enable(struct sock *sk)
b87d8561	76	{
6687e988 ACM	77	const struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	78	struct vegas *vegas = inet_csk_ca(sk);
b87d8561 SH	79
	80	/* Begin taking Vegas samples next time we send something. */
	81	vegas->doing_vegas_now = 1;
	82
	83	/* Set the beginning of the next send window. */
	84	vegas->beg_snd_nxt = tp->snd_nxt;
	85
	86	vegas->cntRTT = 0;
	87	vegas->minRTT = 0x7fffffff;
	88	}
	89
	90	/* Stop taking Vegas samples for now. */
6687e988	91	static inline void vegas_disable(struct sock *sk)
b87d8561	92	{
6687e988	93	struct vegas *vegas = inet_csk_ca(sk);
b87d8561 SH	94
	95	vegas->doing_vegas_now = 0;
	96	}
	97
7752237e	98	void tcp_vegas_init(struct sock *sk)
b87d8561	99	{
6687e988	100	struct vegas *vegas = inet_csk_ca(sk);
b87d8561 SH	101
b87d8561 SH	102	vegas->baseRTT = 0x7fffffff;
6687e988	103	vegas_enable(sk);
b87d8561	104	}
7752237e	105	EXPORT_SYMBOL_GPL(tcp_vegas_init);
b87d8561 SH	106
	107	/* Do RTT sampling needed for Vegas.
	108	* Basically we:
	109	* o min-filter RTT samples from within an RTT to get the current
	110	* propagation delay + queuing delay (we are min-filtering to try to
	111	* avoid the effects of delayed ACKs)
	112	* o min-filter RTT samples from a much longer window (forever for now)
	113	* to find the propagation delay (baseRTT)
	114	*/
30cfd0ba	115	void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
b87d8561	116	{
6687e988	117	struct vegas *vegas = inet_csk_ca(sk);
164891aa SH	118	u32 vrtt;
164891aa SH	119
30cfd0ba	120	if (rtt_us < 0)
b9ce204f IJ	121	return;
b9ce204f IJ	122
164891aa	123	/* Never allow zero rtt or baseRTT */
30cfd0ba	124	vrtt = rtt_us + 1;
b87d8561 SH	125
	126	/* Filter to find propagation delay: */
	127	if (vrtt < vegas->baseRTT)
	128	vegas->baseRTT = vrtt;
	129
	130	/* Find the min RTT during the last RTT to find
	131	* the current prop. delay + queuing delay:
	132	*/
	133	vegas->minRTT = min(vegas->minRTT, vrtt);
	134	vegas->cntRTT++;
	135	}
7752237e	136	EXPORT_SYMBOL_GPL(tcp_vegas_pkts_acked);
b87d8561	137
7752237e	138	void tcp_vegas_state(struct sock *sk, u8 ca_state)
b87d8561 SH	139	{
	140
	141	if (ca_state == TCP_CA_Open)
6687e988	142	vegas_enable(sk);
b87d8561	143	else
6687e988	144	vegas_disable(sk);
b87d8561	145	}
7752237e	146	EXPORT_SYMBOL_GPL(tcp_vegas_state);
b87d8561 SH	147
	148	/*
	149	* If the connection is idle and we are restarting,
	150	* then we don't want to do any Vegas calculations
	151	* until we get fresh RTT samples. So when we
	152	* restart, we reset our Vegas state to a clean
	153	* slate. After we get acks for this flight of
	154	* packets, _then_ we can make Vegas calculations
	155	* again.
	156	*/
7752237e	157	void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)
b87d8561 SH	158	{
	159	if (event == CA_EVENT_CWND_RESTART \|\|
	160	event == CA_EVENT_TX_START)
6687e988	161	tcp_vegas_init(sk);
b87d8561	162	}
7752237e	163	EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);
b87d8561	164
c3a05c60	165	static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
b87d8561	166	{
6687e988 ACM	167	struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	168	struct vegas *vegas = inet_csk_ca(sk);
b87d8561 SH	169
b87d8561 SH	170	if (!vegas->doing_vegas_now)
c3a05c60	171	return tcp_reno_cong_avoid(sk, ack, in_flight);
b87d8561 SH	172
	173	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
	174	*
	175	* These are so named because they represent the approximate values
	176	* of snd_una and snd_nxt at the beginning of the current RTT. More
	177	* precisely, they represent the amount of data sent during the RTT.
	178	* At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
	179	* we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
	180	* bytes of data have been ACKed during the course of the RTT, giving
	181	* an "actual" rate of:
	182	*
	183	* (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
	184	*
	185	* Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
	186	* because delayed ACKs can cover more than one segment, so they
	187	* don't line up nicely with the boundaries of RTTs.
	188	*
	189	* Another unfortunate fact of life is that delayed ACKs delay the
	190	* advance of the left edge of our send window, so that the number
	191	* of bytes we send in an RTT is often less than our cwnd will allow.
	192	* So we keep track of our cwnd separately, in v_beg_snd_cwnd.
	193	*/
	194
	195	if (after(ack, vegas->beg_snd_nxt)) {
	196	/* Do the Vegas once-per-RTT cwnd adjustment. */
	197	u32 old_wnd, old_snd_cwnd;
	198
	199
	200	/* Here old_wnd is essentially the window of data that was
	201	* sent during the previous RTT, and has all
	202	* been acknowledged in the course of the RTT that ended
	203	* with the ACK we just received. Likewise, old_snd_cwnd
	204	* is the cwnd during the previous RTT.
	205	*/
	206	old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
	207	tp->mss_cache;
	208	old_snd_cwnd = vegas->beg_snd_cwnd;
	209
	210	/* Save the extent of the current window so we can use this
	211	* at the end of the next RTT.
	212	*/
	213	vegas->beg_snd_una = vegas->beg_snd_nxt;
	214	vegas->beg_snd_nxt = tp->snd_nxt;
	215	vegas->beg_snd_cwnd = tp->snd_cwnd;
	216
b87d8561 SH	217	/* We do the Vegas calculations only if we got enough RTT
	218	* samples that we can be reasonably sure that we got
	219	* at least one RTT sample that wasn't from a delayed ACK.
	220	* If we only had 2 samples total,
	221	* then that means we're getting only 1 ACK per RTT, which
	222	* means they're almost certainly delayed ACKs.
	223	* If we have 3 samples, we should be OK.
	224	*/
	225
	226	if (vegas->cntRTT <= 2) {
	227	/* We don't have enough RTT samples to do the Vegas
	228	* calculation, so we'll behave like Reno.
	229	*/
c3a05c60	230	tcp_reno_cong_avoid(sk, ack, in_flight);
b87d8561	231	} else {
15913114 LA	232	u32 rtt, diff;
15913114 LA	233	u64 target_cwnd;
b87d8561 SH	234
	235	/* We have enough RTT samples, so, using the Vegas
	236	* algorithm, we determine if we should increase or
	237	* decrease cwnd, and by how much.
	238	*/
	239
	240	/* Pluck out the RTT we are using for the Vegas
	241	* calculations. This is the min RTT seen during the
	242	* last RTT. Taking the min filters out the effects
	243	* of delayed ACKs, at the cost of noticing congestion
	244	* a bit later.
	245	*/
	246	rtt = vegas->minRTT;
	247
	248	/* Calculate the cwnd we should have, if we weren't
	249	* going too fast.
	250	*
	251	* This is:
	252	* (actual rate in segments) * baseRTT
	253	* We keep it as a fixed point number with
	254	* V_PARAM_SHIFT bits to the right of the binary point.
	255	*/
15913114 LA	256	target_cwnd = ((u64)old_wnd * vegas->baseRTT);
	257	target_cwnd <<= V_PARAM_SHIFT;
	258	do_div(target_cwnd, rtt);
b87d8561 SH	259
	260	/* Calculate the difference between the window we had,
	261	* and the window we would like to have. This quantity
	262	* is the "Diff" from the Arizona Vegas papers.
	263	*
	264	* Again, this is a fixed point number with
	265	* V_PARAM_SHIFT bits to the right of the binary
	266	* point.
	267	*/
	268	diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
	269
c940587b XDW	270	if (diff > gamma && tp->snd_ssthresh > 2 ) {
	271	/* Going too fast. Time to slow down
	272	* and switch to congestion avoidance.
	273	*/
	274	tp->snd_ssthresh = 2;
	275
	276	/* Set cwnd to match the actual rate
	277	* exactly:
	278	* cwnd = (actual rate) * baseRTT
	279	* Then we add 1 because the integer
	280	* truncation robs us of full link
	281	* utilization.
	282	*/
	283	tp->snd_cwnd = min(tp->snd_cwnd,
15913114	284	((u32)target_cwnd >>
c940587b	285	V_PARAM_SHIFT)+1);
b87d8561	286
c940587b XDW	287	} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
c940587b XDW	288	/* Slow start. */
7faffa1c	289	tcp_slow_start(tp);
b87d8561 SH	290	} else {
	291	/* Congestion avoidance. */
	292	u32 next_snd_cwnd;
	293
	294	/* Figure out where we would like cwnd
	295	* to be.
	296	*/
	297	if (diff > beta) {
	298	/* The old window was too fast, so
	299	* we slow down.
	300	*/
	301	next_snd_cwnd = old_snd_cwnd - 1;
	302	} else if (diff < alpha) {
	303	/* We don't have enough extra packets
	304	* in the network, so speed up.
	305	*/
	306	next_snd_cwnd = old_snd_cwnd + 1;
	307	} else {
	308	/* Sending just as fast as we
	309	* should be.
	310	*/
	311	next_snd_cwnd = old_snd_cwnd;
	312	}
	313
	314	/* Adjust cwnd upward or downward, toward the
	315	* desired value.
	316	*/
	317	if (next_snd_cwnd > tp->snd_cwnd)
	318	tp->snd_cwnd++;
	319	else if (next_snd_cwnd < tp->snd_cwnd)
	320	tp->snd_cwnd--;
	321	}
b87d8561	322
7faffa1c SH	323	if (tp->snd_cwnd < 2)
	324	tp->snd_cwnd = 2;
	325	else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
	326	tp->snd_cwnd = tp->snd_cwnd_clamp;
	327	}
b87d8561	328
5b495613 TY	329	/* Wipe the slate clean for the next RTT. */
	330	vegas->cntRTT = 0;
	331	vegas->minRTT = 0x7fffffff;
	332	}
74cb8798	333	/* Use normal slow start */
e905a9ed	334	else if (tp->snd_cwnd <= tp->snd_ssthresh)
74cb8798	335	tcp_slow_start(tp);
e905a9ed	336
b87d8561 SH	337	}
	338
	339	/* Extract info for Tcp socket info provided via netlink. */
7752237e	340	void tcp_vegas_get_info(struct sock sk, u32 ext, struct sk_buff skb)
b87d8561	341	{
6687e988	342	const struct vegas *ca = inet_csk_ca(sk);
73c1f4a0	343	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
e9195d67 TG	344	struct tcpvegas_info info = {
	345	.tcpv_enabled = ca->doing_vegas_now,
	346	.tcpv_rttcnt = ca->cntRTT,
	347	.tcpv_rtt = ca->baseRTT,
	348	.tcpv_minrtt = ca->minRTT,
	349	};
	350
	351	nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
b87d8561 SH	352	}
b87d8561 SH	353	}
7752237e	354	EXPORT_SYMBOL_GPL(tcp_vegas_get_info);
b87d8561 SH	355
b87d8561 SH	356	static struct tcp_congestion_ops tcp_vegas = {
164891aa	357	.flags = TCP_CONG_RTT_STAMP,
b87d8561 SH	358	.init = tcp_vegas_init,
	359	.ssthresh = tcp_reno_ssthresh,
	360	.cong_avoid = tcp_vegas_cong_avoid,
	361	.min_cwnd = tcp_reno_min_cwnd,
164891aa	362	.pkts_acked = tcp_vegas_pkts_acked,
b87d8561 SH	363	.set_state = tcp_vegas_state,
	364	.cwnd_event = tcp_vegas_cwnd_event,
	365	.get_info = tcp_vegas_get_info,
	366
	367	.owner = THIS_MODULE,
	368	.name = "vegas",
	369	};
	370
	371	static int __init tcp_vegas_register(void)
	372	{
74975d40	373	BUILD_BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE);
b87d8561 SH	374	tcp_register_congestion_control(&tcp_vegas);
	375	return 0;
	376	}
	377
	378	static void __exit tcp_vegas_unregister(void)
	379	{
	380	tcp_unregister_congestion_control(&tcp_vegas);
	381	}
	382
	383	module_init(tcp_vegas_register);
	384	module_exit(tcp_vegas_unregister);
	385
	386	MODULE_AUTHOR("Stephen Hemminger");
	387	MODULE_LICENSE("GPL");
	388	MODULE_DESCRIPTION("TCP Vegas");