1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * TCP HYBLA
4 *
5 * TCP-HYBLA Congestion control algorithm, based on:
6 *   C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
7 *   for Heterogeneous Networks",
8 *   International Journal on satellite Communications,
9 *				       September 2004
10 *    Daniele Lacamera
11 *    root at danielinux.net
12 */
13
14#include <linux/module.h>
15#include <net/tcp.h>
16
17/* Tcp Hybla structure. */
18struct hybla {
19	bool  hybla_en;
20	u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
21	u32   rho;	      /* Rho parameter, integer part  */
22	u32   rho2;	      /* Rho * Rho, integer part */
23	u32   rho_3ls;	      /* Rho parameter, <<3 */
24	u32   rho2_7ls;	      /* Rho^2, <<7	*/
25	u32   minrtt_us;      /* Minimum smoothed round trip time value seen */
26};
27
28/* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
29static int rtt0 = 25;
30module_param(rtt0, int, 0644);
31MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
32
33/* This is called to refresh values for hybla parameters */
34static inline void hybla_recalc_param (struct sock *sk)
35{
36	struct hybla *ca = inet_csk_ca(sk);
37
38	ca->rho_3ls = max_t(u32,
39			    tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
40			    8U);
41	ca->rho = ca->rho_3ls >> 3;
42	ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
43	ca->rho2 = ca->rho2_7ls >> 7;
44}
45
46static void hybla_init(struct sock *sk)
47{
48	struct tcp_sock *tp = tcp_sk(sk);
49	struct hybla *ca = inet_csk_ca(sk);
50
51	ca->rho = 0;
52	ca->rho2 = 0;
53	ca->rho_3ls = 0;
54	ca->rho2_7ls = 0;
55	ca->snd_cwnd_cents = 0;
56	ca->hybla_en = true;
57	tcp_snd_cwnd_set(tp, 2);
58	tp->snd_cwnd_clamp = 65535;
59
60	/* 1st Rho measurement based on initial srtt */
61	hybla_recalc_param(sk);
62
63	/* set minimum rtt as this is the 1st ever seen */
64	ca->minrtt_us = tp->srtt_us;
65	tcp_snd_cwnd_set(tp, ca->rho);
66}
67
68static void hybla_state(struct sock *sk, u8 ca_state)
69{
70	struct hybla *ca = inet_csk_ca(sk);
71
72	ca->hybla_en = (ca_state == TCP_CA_Open);
73}
74
75static inline u32 hybla_fraction(u32 odds)
76{
77	static const u32 fractions[] = {
78		128, 139, 152, 165, 181, 197, 215, 234,
79	};
80
81	return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
82}
83
84/* TCP Hybla main routine.
85 * This is the algorithm behavior:
86 *     o Recalc Hybla parameters if min_rtt has changed
87 *     o Give cwnd a new value based on the model proposed
88 *     o remember increments <1
89 */
90static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
91{
92	struct tcp_sock *tp = tcp_sk(sk);
93	struct hybla *ca = inet_csk_ca(sk);
94	u32 increment, odd, rho_fractions;
95	int is_slowstart = 0;
96
97	/*  Recalculate rho only if this srtt is the lowest */
98	if (tp->srtt_us < ca->minrtt_us) {
99		hybla_recalc_param(sk);
100		ca->minrtt_us = tp->srtt_us;
101	}
102
103	if (!tcp_is_cwnd_limited(sk))
104		return;
105
106	if (!ca->hybla_en) {
107		tcp_reno_cong_avoid(sk, ack, acked);
108		return;
109	}
110
111	if (ca->rho == 0)
112		hybla_recalc_param(sk);
113
114	rho_fractions = ca->rho_3ls - (ca->rho << 3);
115
116	if (tcp_in_slow_start(tp)) {
117		/*
118		 * slow start
119		 *      INC = 2^RHO - 1
120		 * This is done by splitting the rho parameter
121		 * into 2 parts: an integer part and a fraction part.
122		 * Inrement<<7 is estimated by doing:
123		 *	       [2^(int+fract)]<<7
124		 * that is equal to:
125		 *	       (2^int)	*  [(2^fract) <<7]
126		 * 2^int is straightly computed as 1<<int,
127		 * while we will use hybla_slowstart_fraction_increment() to
128		 * calculate 2^fract in a <<7 value.
129		 */
130		is_slowstart = 1;
131		increment = ((1 << min(ca->rho, 16U)) *
132			hybla_fraction(rho_fractions)) - 128;
133	} else {
134		/*
135		 * congestion avoidance
136		 * INC = RHO^2 / W
137		 * as long as increment is estimated as (rho<<7)/window
138		 * it already is <<7 and we can easily count its fractions.
139		 */
140		increment = ca->rho2_7ls / tcp_snd_cwnd(tp);
141		if (increment < 128)
142			tp->snd_cwnd_cnt++;
143	}
144
145	odd = increment % 128;
146	tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + (increment >> 7));
147	ca->snd_cwnd_cents += odd;
148
149	/* check when fractions goes >=128 and increase cwnd by 1. */
150	while (ca->snd_cwnd_cents >= 128) {
151		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
152		ca->snd_cwnd_cents -= 128;
153		tp->snd_cwnd_cnt = 0;
154	}
155	/* check when cwnd has not been incremented for a while */
156	if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
157		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
158		tp->snd_cwnd_cnt = 0;
159	}
160	/* clamp down slowstart cwnd to ssthresh value. */
161	if (is_slowstart)
162		tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_ssthresh));
163
164	tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
165}
166
167static struct tcp_congestion_ops tcp_hybla __read_mostly = {
168	.init		= hybla_init,
169	.ssthresh	= tcp_reno_ssthresh,
170	.undo_cwnd	= tcp_reno_undo_cwnd,
171	.cong_avoid	= hybla_cong_avoid,
172	.set_state	= hybla_state,
173
174	.owner		= THIS_MODULE,
175	.name		= "hybla"
176};
177
178static int __init hybla_register(void)
179{
180	BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
181	return tcp_register_congestion_control(&tcp_hybla);
182}
183
184static void __exit hybla_unregister(void)
185{
186	tcp_unregister_congestion_control(&tcp_hybla);
187}
188
189module_init(hybla_register);
190module_exit(hybla_unregister);
191
192MODULE_AUTHOR("Daniele Lacamera");
193MODULE_LICENSE("GPL");
194MODULE_DESCRIPTION("TCP Hybla");
195