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 (tcp_in_slow_start(tp)) {
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 .undo_cwnd = tcp_reno_undo_cwnd,
170 .cong_avoid = hybla_cong_avoid,
171 .set_state = hybla_state,
172
173 .owner = THIS_MODULE,
174 .name = "hybla"
175};
176
177static int __init hybla_register(void)
178{
179 BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
180 return tcp_register_congestion_control(&tcp_hybla);
181}
182
183static void __exit hybla_unregister(void)
184{
185 tcp_unregister_congestion_control(&tcp_hybla);
186}
187
188module_init(hybla_register);
189module_exit(hybla_unregister);
190
191MODULE_AUTHOR("Daniele Lacamera");
192MODULE_LICENSE("GPL");
193MODULE_DESCRIPTION("TCP Hybla");
194