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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * H-TCP congestion control. The algorithm is detailed in:
4 * R.N.Shorten, D.J.Leith:
5 * "H-TCP: TCP for high-speed and long-distance networks"
6 * Proc. PFLDnet, Argonne, 2004.
7 * https://www.hamilton.ie/net/htcp3.pdf
8 */
9
10#include <linux/mm.h>
11#include <linux/module.h>
12#include <net/tcp.h>
13
14#define ALPHA_BASE (1<<7) /* 1.0 with shift << 7 */
15#define BETA_MIN (1<<6) /* 0.5 with shift << 7 */
16#define BETA_MAX 102 /* 0.8 with shift << 7 */
17
18static int use_rtt_scaling __read_mostly = 1;
19module_param(use_rtt_scaling, int, 0644);
20MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
21
22static int use_bandwidth_switch __read_mostly = 1;
23module_param(use_bandwidth_switch, int, 0644);
24MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
25
26struct htcp {
27 u32 alpha; /* Fixed point arith, << 7 */
28 u8 beta; /* Fixed point arith, << 7 */
29 u8 modeswitch; /* Delay modeswitch
30 until we had at least one congestion event */
31 u16 pkts_acked;
32 u32 packetcount;
33 u32 minRTT;
34 u32 maxRTT;
35 u32 last_cong; /* Time since last congestion event end */
36 u32 undo_last_cong;
37
38 u32 undo_maxRTT;
39 u32 undo_old_maxB;
40
41 /* Bandwidth estimation */
42 u32 minB;
43 u32 maxB;
44 u32 old_maxB;
45 u32 Bi;
46 u32 lasttime;
47};
48
49static inline u32 htcp_cong_time(const struct htcp *ca)
50{
51 return jiffies - ca->last_cong;
52}
53
54static inline u32 htcp_ccount(const struct htcp *ca)
55{
56 return htcp_cong_time(ca) / ca->minRTT;
57}
58
59static inline void htcp_reset(struct htcp *ca)
60{
61 ca->undo_last_cong = ca->last_cong;
62 ca->undo_maxRTT = ca->maxRTT;
63 ca->undo_old_maxB = ca->old_maxB;
64
65 ca->last_cong = jiffies;
66}
67
68static u32 htcp_cwnd_undo(struct sock *sk)
69{
70 struct htcp *ca = inet_csk_ca(sk);
71
72 if (ca->undo_last_cong) {
73 ca->last_cong = ca->undo_last_cong;
74 ca->maxRTT = ca->undo_maxRTT;
75 ca->old_maxB = ca->undo_old_maxB;
76 ca->undo_last_cong = 0;
77 }
78
79 return tcp_reno_undo_cwnd(sk);
80}
81
82static inline void measure_rtt(struct sock *sk, u32 srtt)
83{
84 const struct inet_connection_sock *icsk = inet_csk(sk);
85 struct htcp *ca = inet_csk_ca(sk);
86
87 /* keep track of minimum RTT seen so far, minRTT is zero at first */
88 if (ca->minRTT > srtt || !ca->minRTT)
89 ca->minRTT = srtt;
90
91 /* max RTT */
92 if (icsk->icsk_ca_state == TCP_CA_Open) {
93 if (ca->maxRTT < ca->minRTT)
94 ca->maxRTT = ca->minRTT;
95 if (ca->maxRTT < srtt &&
96 srtt <= ca->maxRTT + msecs_to_jiffies(20))
97 ca->maxRTT = srtt;
98 }
99}
100
101static void measure_achieved_throughput(struct sock *sk,
102 const struct ack_sample *sample)
103{
104 const struct inet_connection_sock *icsk = inet_csk(sk);
105 const struct tcp_sock *tp = tcp_sk(sk);
106 struct htcp *ca = inet_csk_ca(sk);
107 u32 now = tcp_jiffies32;
108
109 if (icsk->icsk_ca_state == TCP_CA_Open)
110 ca->pkts_acked = sample->pkts_acked;
111
112 if (sample->rtt_us > 0)
113 measure_rtt(sk, usecs_to_jiffies(sample->rtt_us));
114
115 if (!use_bandwidth_switch)
116 return;
117
118 /* achieved throughput calculations */
119 if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) {
120 ca->packetcount = 0;
121 ca->lasttime = now;
122 return;
123 }
124
125 ca->packetcount += sample->pkts_acked;
126
127 if (ca->packetcount >= tcp_snd_cwnd(tp) - (ca->alpha >> 7 ? : 1) &&
128 now - ca->lasttime >= ca->minRTT &&
129 ca->minRTT > 0) {
130 __u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);
131
132 if (htcp_ccount(ca) <= 3) {
133 /* just after backoff */
134 ca->minB = ca->maxB = ca->Bi = cur_Bi;
135 } else {
136 ca->Bi = (3 * ca->Bi + cur_Bi) / 4;
137 if (ca->Bi > ca->maxB)
138 ca->maxB = ca->Bi;
139 if (ca->minB > ca->maxB)
140 ca->minB = ca->maxB;
141 }
142 ca->packetcount = 0;
143 ca->lasttime = now;
144 }
145}
146
147static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
148{
149 if (use_bandwidth_switch) {
150 u32 maxB = ca->maxB;
151 u32 old_maxB = ca->old_maxB;
152
153 ca->old_maxB = ca->maxB;
154 if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) {
155 ca->beta = BETA_MIN;
156 ca->modeswitch = 0;
157 return;
158 }
159 }
160
161 if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
162 ca->beta = (minRTT << 7) / maxRTT;
163 if (ca->beta < BETA_MIN)
164 ca->beta = BETA_MIN;
165 else if (ca->beta > BETA_MAX)
166 ca->beta = BETA_MAX;
167 } else {
168 ca->beta = BETA_MIN;
169 ca->modeswitch = 1;
170 }
171}
172
173static inline void htcp_alpha_update(struct htcp *ca)
174{
175 u32 minRTT = ca->minRTT;
176 u32 factor = 1;
177 u32 diff = htcp_cong_time(ca);
178
179 if (diff > HZ) {
180 diff -= HZ;
181 factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ;
182 }
183
184 if (use_rtt_scaling && minRTT) {
185 u32 scale = (HZ << 3) / (10 * minRTT);
186
187 /* clamping ratio to interval [0.5,10]<<3 */
188 scale = clamp(scale, 1U << 2, 10U << 3);
189 factor = (factor << 3) / scale;
190 if (!factor)
191 factor = 1;
192 }
193
194 ca->alpha = 2 * factor * ((1 << 7) - ca->beta);
195 if (!ca->alpha)
196 ca->alpha = ALPHA_BASE;
197}
198
199/*
200 * After we have the rtt data to calculate beta, we'd still prefer to wait one
201 * rtt before we adjust our beta to ensure we are working from a consistent
202 * data.
203 *
204 * This function should be called when we hit a congestion event since only at
205 * that point do we really have a real sense of maxRTT (the queues en route
206 * were getting just too full now).
207 */
208static void htcp_param_update(struct sock *sk)
209{
210 struct htcp *ca = inet_csk_ca(sk);
211 u32 minRTT = ca->minRTT;
212 u32 maxRTT = ca->maxRTT;
213
214 htcp_beta_update(ca, minRTT, maxRTT);
215 htcp_alpha_update(ca);
216
217 /* add slowly fading memory for maxRTT to accommodate routing changes */
218 if (minRTT > 0 && maxRTT > minRTT)
219 ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100;
220}
221
222static u32 htcp_recalc_ssthresh(struct sock *sk)
223{
224 const struct tcp_sock *tp = tcp_sk(sk);
225 const struct htcp *ca = inet_csk_ca(sk);
226
227 htcp_param_update(sk);
228 return max((tcp_snd_cwnd(tp) * ca->beta) >> 7, 2U);
229}
230
231static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
232{
233 struct tcp_sock *tp = tcp_sk(sk);
234 struct htcp *ca = inet_csk_ca(sk);
235
236 if (!tcp_is_cwnd_limited(sk))
237 return;
238
239 if (tcp_in_slow_start(tp))
240 tcp_slow_start(tp, acked);
241 else {
242 /* In dangerous area, increase slowly.
243 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
244 */
245 if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tcp_snd_cwnd(tp)) {
246 if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp)
247 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
248 tp->snd_cwnd_cnt = 0;
249 htcp_alpha_update(ca);
250 } else
251 tp->snd_cwnd_cnt += ca->pkts_acked;
252
253 ca->pkts_acked = 1;
254 }
255}
256
257static void htcp_init(struct sock *sk)
258{
259 struct htcp *ca = inet_csk_ca(sk);
260
261 memset(ca, 0, sizeof(struct htcp));
262 ca->alpha = ALPHA_BASE;
263 ca->beta = BETA_MIN;
264 ca->pkts_acked = 1;
265 ca->last_cong = jiffies;
266}
267
268static void htcp_state(struct sock *sk, u8 new_state)
269{
270 switch (new_state) {
271 case TCP_CA_Open:
272 {
273 struct htcp *ca = inet_csk_ca(sk);
274
275 if (ca->undo_last_cong) {
276 ca->last_cong = jiffies;
277 ca->undo_last_cong = 0;
278 }
279 }
280 break;
281 case TCP_CA_CWR:
282 case TCP_CA_Recovery:
283 case TCP_CA_Loss:
284 htcp_reset(inet_csk_ca(sk));
285 break;
286 }
287}
288
289static struct tcp_congestion_ops htcp __read_mostly = {
290 .init = htcp_init,
291 .ssthresh = htcp_recalc_ssthresh,
292 .cong_avoid = htcp_cong_avoid,
293 .set_state = htcp_state,
294 .undo_cwnd = htcp_cwnd_undo,
295 .pkts_acked = measure_achieved_throughput,
296 .owner = THIS_MODULE,
297 .name = "htcp",
298};
299
300static int __init htcp_register(void)
301{
302 BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
303 BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
304 return tcp_register_congestion_control(&htcp);
305}
306
307static void __exit htcp_unregister(void)
308{
309 tcp_unregister_congestion_control(&htcp);
310}
311
312module_init(htcp_register);
313module_exit(htcp_unregister);
314
315MODULE_AUTHOR("Baruch Even");
316MODULE_LICENSE("GPL");
317MODULE_DESCRIPTION("H-TCP");