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. */
18 struct 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 */
29 static int rtt0 = 25;
30 module_param(rtt0, int, 0644);
31 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
32
33 /* This is called to refresh values for hybla parameters */
34 static 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
46 static 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
68 static 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
75 static 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 */
90 static 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
167 static 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
178 static 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
184 static void __exit hybla_unregister(void)
185 {
186 tcp_unregister_congestion_control(&tcp_hybla);
187 }
188
189 module_init(hybla_register);
190 module_exit(hybla_unregister);
191
192 MODULE_AUTHOR("Daniele Lacamera");
193 MODULE_LICENSE("GPL");
194 MODULE_DESCRIPTION("TCP Hybla");
195
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