xref: /linux/net/ipv4/tcp_htcp.c (revision 9410645520e9b820069761f3450ef6661418e279)
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 
18 static int use_rtt_scaling __read_mostly = 1;
19 module_param(use_rtt_scaling, int, 0644);
20 MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
21 
22 static int use_bandwidth_switch __read_mostly = 1;
23 module_param(use_bandwidth_switch, int, 0644);
24 MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
25 
26 struct 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 
htcp_cong_time(const struct htcp * ca)49 static inline u32 htcp_cong_time(const struct htcp *ca)
50 {
51 	return jiffies - ca->last_cong;
52 }
53 
htcp_ccount(const struct htcp * ca)54 static inline u32 htcp_ccount(const struct htcp *ca)
55 {
56 	return htcp_cong_time(ca) / ca->minRTT;
57 }
58 
htcp_reset(struct htcp * ca)59 static 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 
htcp_cwnd_undo(struct sock * sk)68 static 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 
measure_rtt(struct sock * sk,u32 srtt)82 static 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 
measure_achieved_throughput(struct sock * sk,const struct ack_sample * sample)101 static 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 
htcp_beta_update(struct htcp * ca,u32 minRTT,u32 maxRTT)147 static 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 
htcp_alpha_update(struct htcp * ca)173 static 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  */
htcp_param_update(struct sock * sk)208 static 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 
htcp_recalc_ssthresh(struct sock * sk)222 static 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 
htcp_cong_avoid(struct sock * sk,u32 ack,u32 acked)231 static 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 
htcp_init(struct sock * sk)257 static 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 
htcp_state(struct sock * sk,u8 new_state)268 static 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 
289 static 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 
htcp_register(void)300 static 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 
htcp_unregister(void)307 static void __exit htcp_unregister(void)
308 {
309 	tcp_unregister_congestion_control(&htcp);
310 }
311 
312 module_init(htcp_register);
313 module_exit(htcp_unregister);
314 
315 MODULE_AUTHOR("Baruch Even");
316 MODULE_LICENSE("GPL");
317 MODULE_DESCRIPTION("H-TCP");
318