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	u8    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;	      /* Minimum smoothed round trip time value seen */
25};
26
27/* Hybla reference round trip time (default= 1/40 sec = 25 ms),
28   expressed in jiffies */
29static int rtt0 = 25;
30module_param(rtt0, int, 0644);
31MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
32
33
34/* This is called to refresh values for hybla parameters */
35static inline void hybla_recalc_param (struct sock *sk)
36{
37	struct hybla *ca = inet_csk_ca(sk);
38
39	ca->rho_3ls = max_t(u32, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8);
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 = 1;
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 = tp->srtt;
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	ca->hybla_en = (ca_state == TCP_CA_Open);
71}
72
73static inline u32 hybla_fraction(u32 odds)
74{
75	static const u32 fractions[] = {
76		128, 139, 152, 165, 181, 197, 215, 234,
77	};
78
79	return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
80}
81
82/* TCP Hybla main routine.
83 * This is the algorithm behavior:
84 *     o Recalc Hybla parameters if min_rtt has changed
85 *     o Give cwnd a new value based on the model proposed
86 *     o remember increments <1
87 */
88static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
89			    u32 in_flight, int flag)
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 < ca->minrtt){
98		hybla_recalc_param(sk);
99		ca->minrtt = tp->srtt;
100	}
101
102	if (!tcp_is_cwnd_limited(sk, in_flight))
103		return;
104
105	if (!ca->hybla_en)
106		return tcp_reno_cong_avoid(sk, ack, rtt, in_flight, flag);
107
108	if (ca->rho == 0)
109		hybla_recalc_param(sk);
110
111	rho_fractions = ca->rho_3ls - (ca->rho << 3);
112
113	if (tp->snd_cwnd < tp->snd_ssthresh) {
114		/*
115		 * slow start
116		 *      INC = 2^RHO - 1
117		 * This is done by splitting the rho parameter
118		 * into 2 parts: an integer part and a fraction part.
119		 * Inrement<<7 is estimated by doing:
120		 *	       [2^(int+fract)]<<7
121		 * that is equal to:
122		 *	       (2^int)	*  [(2^fract) <<7]
123		 * 2^int is straightly computed as 1<<int,
124		 * while we will use hybla_slowstart_fraction_increment() to
125		 * calculate 2^fract in a <<7 value.
126		 */
127		is_slowstart = 1;
128		increment = ((1 << ca->rho) * hybla_fraction(rho_fractions))
129			- 128;
130	} else {
131		/*
132		 * congestion avoidance
133		 * INC = RHO^2 / W
134		 * as long as increment is estimated as (rho<<7)/window
135		 * it already is <<7 and we can easily count its fractions.
136		 */
137		increment = ca->rho2_7ls / tp->snd_cwnd;
138		if (increment < 128)
139			tp->snd_cwnd_cnt++;
140	}
141
142	odd = increment % 128;
143	tp->snd_cwnd += increment >> 7;
144	ca->snd_cwnd_cents += odd;
145
146	/* check when fractions goes >=128 and increase cwnd by 1. */
147	while (ca->snd_cwnd_cents >= 128) {
148		tp->snd_cwnd++;
149		ca->snd_cwnd_cents -= 128;
150		tp->snd_cwnd_cnt = 0;
151	}
152
153	/* clamp down slowstart cwnd to ssthresh value. */
154	if (is_slowstart)
155		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
156
157	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
158}
159
160static struct tcp_congestion_ops tcp_hybla = {
161	.init		= hybla_init,
162	.ssthresh	= tcp_reno_ssthresh,
163	.min_cwnd	= tcp_reno_min_cwnd,
164	.cong_avoid	= hybla_cong_avoid,
165	.set_state	= hybla_state,
166
167	.owner		= THIS_MODULE,
168	.name		= "hybla"
169};
170
171static int __init hybla_register(void)
172{
173	BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
174	return tcp_register_congestion_control(&tcp_hybla);
175}
176
177static void __exit hybla_unregister(void)
178{
179	tcp_unregister_congestion_control(&tcp_hybla);
180}
181
182module_init(hybla_register);
183module_exit(hybla_unregister);
184
185MODULE_AUTHOR("Daniele Lacamera");
186MODULE_LICENSE("GPL");
187MODULE_DESCRIPTION("TCP Hybla");
188