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-rw-r--r--net/ipv4/tcp_hybla.c187
1 files changed, 187 insertions, 0 deletions
diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c
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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/config.h>
14#include <linux/module.h>
15#include <net/tcp.h>
16
17/* Tcp Hybla structure. */
18struct hybla {
19 u8 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; /* Minimum smoothed round trip time value seen */
26};
27
28/* Hybla reference round trip time (default= 1/40 sec = 25 ms),
29 expressed in jiffies */
30static int rtt0 = 25;
31module_param(rtt0, int, 0644);
32MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
33
34
35/* This is called to refresh values for hybla parameters */
36static inline void hybla_recalc_param (struct tcp_sock *tp)
37{
38 struct hybla *ca = tcp_ca(tp);
39
40 ca->rho_3ls = max_t(u32, tp->srtt / msecs_to_jiffies(rtt0), 8);
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 tcp_sock *tp)
47{
48 struct hybla *ca = tcp_ca(tp);
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(tp);
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 tcp_sock *tp, u8 ca_state)
68{
69 struct hybla *ca = tcp_ca(tp);
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 tcp_sock *tp, u32 ack, u32 rtt,
90 u32 in_flight, int flag)
91{
92 struct hybla *ca = tcp_ca(tp);
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(tp);
99 ca->minrtt = tp->srtt;
100 }
101
102 if (!ca->hybla_en)
103 return tcp_reno_cong_avoid(tp, ack, rtt, in_flight, flag);
104
105 if (in_flight < tp->snd_cwnd)
106 return;
107
108 if (ca->rho == 0)
109 hybla_recalc_param(tp);
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 BUG_ON(sizeof(struct hybla) > TCP_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");
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