1/*
2 * H-TCP congestion control. The algorithm is detailed in:
3 * R.N.Shorten, D.J.Leith:
4 * "H-TCP: TCP for high-speed and long-distance networks"
5 * Proc. PFLDnet, Argonne, 2004.
6 * http://www.hamilton.ie/net/htcp3.pdf
7 */
8
9#include <linux/mm.h>
10#include <linux/module.h>
11#include <net/tcp.h>
12
13#define ALPHA_BASE (1<<7) /* 1.0 with shift << 7 */
14#define BETA_MIN (1<<6) /* 0.5 with shift << 7 */
15#define BETA_MAX 102 /* 0.8 with shift << 7 */
16
17static int use_rtt_scaling __read_mostly = 1;
18module_param(use_rtt_scaling, int, 0644);
19MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
20
21static int use_bandwidth_switch __read_mostly = 1;
22module_param(use_bandwidth_switch, int, 0644);
23MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
24
25struct htcp {
26 u32 alpha; /* Fixed point arith, << 7 */
27 u8 beta; /* Fixed point arith, << 7 */
28 u8 modeswitch; /* Delay modeswitch
29 until we had at least one congestion event */
30 u16 pkts_acked;
31 u32 packetcount;
32 u32 minRTT;
33 u32 maxRTT;
34 u32 last_cong; /* Time since last congestion event end */
35 u32 undo_last_cong;
36
37 u32 undo_maxRTT;
38 u32 undo_old_maxB;
39
40 /* Bandwidth estimation */
41 u32 minB;
42 u32 maxB;
43 u32 old_maxB;
44 u32 Bi;
45 u32 lasttime;
46};
47
48static inline u32 htcp_cong_time(const struct htcp *ca)
49{
50 return jiffies - ca->last_cong;
51}
52
53static inline u32 htcp_ccount(const struct htcp *ca)
54{
55 return htcp_cong_time(ca) / ca->minRTT;
56}
57
58static inline void htcp_reset(struct htcp *ca)
59{
60 ca->undo_last_cong = ca->last_cong;
61 ca->undo_maxRTT = ca->maxRTT;
62 ca->undo_old_maxB = ca->old_maxB;
63
64 ca->last_cong = jiffies;
65}
66
67static u32 htcp_cwnd_undo(struct sock *sk)
68{
69 struct htcp *ca = inet_csk_ca(sk);
70
71 if (ca->undo_last_cong) {
72 ca->last_cong = ca->undo_last_cong;
73 ca->maxRTT = ca->undo_maxRTT;
74 ca->old_maxB = ca->undo_old_maxB;
75 ca->undo_last_cong = 0;
76 }
77
78 return tcp_reno_undo_cwnd(sk);
79}
80
81static inline void measure_rtt(struct sock *sk, u32 srtt)
82{
83 const struct inet_connection_sock *icsk = inet_csk(sk);
84 struct htcp *ca = inet_csk_ca(sk);
85
86 /* keep track of minimum RTT seen so far, minRTT is zero at first */
87 if (ca->minRTT > srtt || !ca->minRTT)
88 ca->minRTT = srtt;
89
90 /* max RTT */
91 if (icsk->icsk_ca_state == TCP_CA_Open) {
92 if (ca->maxRTT < ca->minRTT)
93 ca->maxRTT = ca->minRTT;
94 if (ca->maxRTT < srtt &&
95 srtt <= ca->maxRTT + msecs_to_jiffies(20))
96 ca->maxRTT = srtt;
97 }
98}
99
100static void measure_achieved_throughput(struct sock *sk,
101 const struct ack_sample *sample)
102{
103 const struct inet_connection_sock *icsk = inet_csk(sk);
104 const struct tcp_sock *tp = tcp_sk(sk);
105 struct htcp *ca = inet_csk_ca(sk);
106 u32 now = tcp_jiffies32;
107
108 if (icsk->icsk_ca_state == TCP_CA_Open)
109 ca->pkts_acked = sample->pkts_acked;
110
111 if (sample->rtt_us > 0)
112 measure_rtt(sk, usecs_to_jiffies(sample->rtt_us));
113
114 if (!use_bandwidth_switch)
115 return;
116
117 /* achieved throughput calculations */
118 if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) {
119 ca->packetcount = 0;
120 ca->lasttime = now;
121 return;
122 }
123
124 ca->packetcount += sample->pkts_acked;
125
126 if (ca->packetcount >= tp->snd_cwnd - (ca->alpha >> 7 ? : 1) &&
127 now - ca->lasttime >= ca->minRTT &&
128 ca->minRTT > 0) {
129 __u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);
130
131 if (htcp_ccount(ca) <= 3) {
132 /* just after backoff */
133 ca->minB = ca->maxB = ca->Bi = cur_Bi;
134 } else {
135 ca->Bi = (3 * ca->Bi + cur_Bi) / 4;
136 if (ca->Bi > ca->maxB)
137 ca->maxB = ca->Bi;
138 if (ca->minB > ca->maxB)
139 ca->minB = ca->maxB;
140 }
141 ca->packetcount = 0;
142 ca->lasttime = now;
143 }
144}
145
146static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
147{
148 if (use_bandwidth_switch) {
149 u32 maxB = ca->maxB;
150 u32 old_maxB = ca->old_maxB;
151
152 ca->old_maxB = ca->maxB;
153 if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) {
154 ca->beta = BETA_MIN;
155 ca->modeswitch = 0;
156 return;
157 }
158 }
159
160 if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
161 ca->beta = (minRTT << 7) / maxRTT;
162 if (ca->beta < BETA_MIN)
163 ca->beta = BETA_MIN;
164 else if (ca->beta > BETA_MAX)
165 ca->beta = BETA_MAX;
166 } else {
167 ca->beta = BETA_MIN;
168 ca->modeswitch = 1;
169 }
170}
171
172static inline void htcp_alpha_update(struct htcp *ca)
173{
174 u32 minRTT = ca->minRTT;
175 u32 factor = 1;
176 u32 diff = htcp_cong_time(ca);
177
178 if (diff > HZ) {
179 diff -= HZ;
180 factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ;
181 }
182
183 if (use_rtt_scaling && minRTT) {
184 u32 scale = (HZ << 3) / (10 * minRTT);
185
186 /* clamping ratio to interval [0.5,10]<<3 */
187 scale = min(max(scale, 1U << 2), 10U << 3);
188 factor = (factor << 3) / scale;
189 if (!factor)
190 factor = 1;
191 }
192
193 ca->alpha = 2 * factor * ((1 << 7) - ca->beta);
194 if (!ca->alpha)
195 ca->alpha = ALPHA_BASE;
196}
197
198/*
199 * After we have the rtt data to calculate beta, we'd still prefer to wait one
200 * rtt before we adjust our beta to ensure we are working from a consistent
201 * data.
202 *
203 * This function should be called when we hit a congestion event since only at
204 * that point do we really have a real sense of maxRTT (the queues en route
205 * were getting just too full now).
206 */
207static void htcp_param_update(struct sock *sk)
208{
209 struct htcp *ca = inet_csk_ca(sk);
210 u32 minRTT = ca->minRTT;
211 u32 maxRTT = ca->maxRTT;
212
213 htcp_beta_update(ca, minRTT, maxRTT);
214 htcp_alpha_update(ca);
215
216 /* add slowly fading memory for maxRTT to accommodate routing changes */
217 if (minRTT > 0 && maxRTT > minRTT)
218 ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100;
219}
220
221static u32 htcp_recalc_ssthresh(struct sock *sk)
222{
223 const struct tcp_sock *tp = tcp_sk(sk);
224 const struct htcp *ca = inet_csk_ca(sk);
225
226 htcp_param_update(sk);
227 return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
228}
229
230static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
231{
232 struct tcp_sock *tp = tcp_sk(sk);
233 struct htcp *ca = inet_csk_ca(sk);
234
235 if (!tcp_is_cwnd_limited(sk))
236 return;
237
238 if (tcp_in_slow_start(tp))
239 tcp_slow_start(tp, acked);
240 else {
241 /* In dangerous area, increase slowly.
242 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
243 */
244 if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
245 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
246 tp->snd_cwnd++;
247 tp->snd_cwnd_cnt = 0;
248 htcp_alpha_update(ca);
249 } else
250 tp->snd_cwnd_cnt += ca->pkts_acked;
251
252 ca->pkts_acked = 1;
253 }
254}
255
256static void htcp_init(struct sock *sk)
257{
258 struct htcp *ca = inet_csk_ca(sk);
259
260 memset(ca, 0, sizeof(struct htcp));
261 ca->alpha = ALPHA_BASE;
262 ca->beta = BETA_MIN;
263 ca->pkts_acked = 1;
264 ca->last_cong = jiffies;
265}
266
267static void htcp_state(struct sock *sk, u8 new_state)
268{
269 switch (new_state) {
270 case TCP_CA_Open:
271 {
272 struct htcp *ca = inet_csk_ca(sk);
273
274 if (ca->undo_last_cong) {
275 ca->last_cong = jiffies;
276 ca->undo_last_cong = 0;
277 }
278 }
279 break;
280 case TCP_CA_CWR:
281 case TCP_CA_Recovery:
282 case TCP_CA_Loss:
283 htcp_reset(inet_csk_ca(sk));
284 break;
285 }
286}
287
288static struct tcp_congestion_ops htcp __read_mostly = {
289 .init = htcp_init,
290 .ssthresh = htcp_recalc_ssthresh,
291 .cong_avoid = htcp_cong_avoid,
292 .set_state = htcp_state,
293 .undo_cwnd = htcp_cwnd_undo,
294 .pkts_acked = measure_achieved_throughput,
295 .owner = THIS_MODULE,
296 .name = "htcp",
297};
298
299static int __init htcp_register(void)
300{
301 BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
302 BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
303 return tcp_register_congestion_control(&htcp);
304}
305
306static void __exit htcp_unregister(void)
307{
308 tcp_unregister_congestion_control(&htcp);
309}
310
311module_init(htcp_register);
312module_exit(htcp_unregister);
313
314MODULE_AUTHOR("Baruch Even");
315MODULE_LICENSE("GPL");
316MODULE_DESCRIPTION("H-TCP");
317