1/*
2 * TCP HYBLA
3 *
4 * TCP-HYBLA Congestion control algorithm, based on:
5 *   C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
6 *   for Heterogeneous Networks",
7 *   International Journal on satellite Communications,
8 *				       September 2004
9 *    Daniele Lacamera
10 *    root at danielinux.net
11 */
12
13#include <linux/module.h>
14#include <net/tcp.h>
15
16/* Tcp Hybla structure. */
17struct hybla {
18	bool  hybla_en;
19	u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
20	u32   rho;	      /* Rho parameter, integer part  */
21	u32   rho2;	      /* Rho * Rho, integer part */
22	u32   rho_3ls;	      /* Rho parameter, <<3 */
23	u32   rho2_7ls;	      /* Rho^2, <<7	*/
24	u32   minrtt_us;      /* Minimum smoothed round trip time value seen */
25};
26
27/* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
28static int rtt0 = 25;
29module_param(rtt0, int, 0644);
30MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
31
32/* This is called to refresh values for hybla parameters */
33static inline void hybla_recalc_param (struct sock *sk)
34{
35	struct hybla *ca = inet_csk_ca(sk);
36
37	ca->rho_3ls = max_t(u32,
38			    tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
39			    8U);
40	ca->rho = ca->rho_3ls >> 3;
41	ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
42	ca->rho2 = ca->rho2_7ls >> 7;
43}
44
45static void hybla_init(struct sock *sk)
46{
47	struct tcp_sock *tp = tcp_sk(sk);
48	struct hybla *ca = inet_csk_ca(sk);
49
50	ca->rho = 0;
51	ca->rho2 = 0;
52	ca->rho_3ls = 0;
53	ca->rho2_7ls = 0;
54	ca->snd_cwnd_cents = 0;
55	ca->hybla_en = true;
56	tp->snd_cwnd = 2;
57	tp->snd_cwnd_clamp = 65535;
58
59	/* 1st Rho measurement based on initial srtt */
60	hybla_recalc_param(sk);
61
62	/* set minimum rtt as this is the 1st ever seen */
63	ca->minrtt_us = tp->srtt_us;
64	tp->snd_cwnd = ca->rho;
65}
66
67static void hybla_state(struct sock *sk, u8 ca_state)
68{
69	struct hybla *ca = inet_csk_ca(sk);
70
71	ca->hybla_en = (ca_state == TCP_CA_Open);
72}
73
74static inline u32 hybla_fraction(u32 odds)
75{
76	static const u32 fractions[] = {
77		128, 139, 152, 165, 181, 197, 215, 234,
78	};
79
80	return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
81}
82
83/* TCP Hybla main routine.
84 * This is the algorithm behavior:
85 *     o Recalc Hybla parameters if min_rtt has changed
86 *     o Give cwnd a new value based on the model proposed
87 *     o remember increments <1
88 */
89static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
90{
91	struct tcp_sock *tp = tcp_sk(sk);
92	struct hybla *ca = inet_csk_ca(sk);
93	u32 increment, odd, rho_fractions;
94	int is_slowstart = 0;
95
96	/*  Recalculate rho only if this srtt is the lowest */
97	if (tp->srtt_us < ca->minrtt_us) {
98		hybla_recalc_param(sk);
99		ca->minrtt_us = tp->srtt_us;
100	}
101
102	if (!tcp_is_cwnd_limited(sk))
103		return;
104
105	if (!ca->hybla_en) {
106		tcp_reno_cong_avoid(sk, ack, acked);
107		return;
108	}
109
110	if (ca->rho == 0)
111		hybla_recalc_param(sk);
112
113	rho_fractions = ca->rho_3ls - (ca->rho << 3);
114
115	if (tp->snd_cwnd < tp->snd_ssthresh) {
116		/*
117		 * slow start
118		 *      INC = 2^RHO - 1
119		 * This is done by splitting the rho parameter
120		 * into 2 parts: an integer part and a fraction part.
121		 * Inrement<<7 is estimated by doing:
122		 *	       [2^(int+fract)]<<7
123		 * that is equal to:
124		 *	       (2^int)	*  [(2^fract) <<7]
125		 * 2^int is straightly computed as 1<<int,
126		 * while we will use hybla_slowstart_fraction_increment() to
127		 * calculate 2^fract in a <<7 value.
128		 */
129		is_slowstart = 1;
130		increment = ((1 << min(ca->rho, 16U)) *
131			hybla_fraction(rho_fractions)) - 128;
132	} else {
133		/*
134		 * congestion avoidance
135		 * INC = RHO^2 / W
136		 * as long as increment is estimated as (rho<<7)/window
137		 * it already is <<7 and we can easily count its fractions.
138		 */
139		increment = ca->rho2_7ls / tp->snd_cwnd;
140		if (increment < 128)
141			tp->snd_cwnd_cnt++;
142	}
143
144	odd = increment % 128;
145	tp->snd_cwnd += increment >> 7;
146	ca->snd_cwnd_cents += odd;
147
148	/* check when fractions goes >=128 and increase cwnd by 1. */
149	while (ca->snd_cwnd_cents >= 128) {
150		tp->snd_cwnd++;
151		ca->snd_cwnd_cents -= 128;
152		tp->snd_cwnd_cnt = 0;
153	}
154	/* check when cwnd has not been incremented for a while */
155	if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
156		tp->snd_cwnd++;
157		tp->snd_cwnd_cnt = 0;
158	}
159	/* clamp down slowstart cwnd to ssthresh value. */
160	if (is_slowstart)
161		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
162
163	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
164}
165
166static struct tcp_congestion_ops tcp_hybla __read_mostly = {
167	.init		= hybla_init,
168	.ssthresh	= tcp_reno_ssthresh,
169	.cong_avoid	= hybla_cong_avoid,
170	.set_state	= hybla_state,
171
172	.owner		= THIS_MODULE,
173	.name		= "hybla"
174};
175
176static int __init hybla_register(void)
177{
178	BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
179	return tcp_register_congestion_control(&tcp_hybla);
180}
181
182static void __exit hybla_unregister(void)
183{
184	tcp_unregister_congestion_control(&tcp_hybla);
185}
186
187module_init(hybla_register);
188module_exit(hybla_unregister);
189
190MODULE_AUTHOR("Daniele Lacamera");
191MODULE_LICENSE("GPL");
192MODULE_DESCRIPTION("TCP Hybla");
193