aboutsummaryrefslogtreecommitdiff
path: root/net/ipv4/tcp_htcp.c
blob: 55adcfcf96feaca1032198c1931e569ee80b3668 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
// SPDX-License-Identifier: GPL-2.0-only
/*
 * H-TCP congestion control. The algorithm is detailed in:
 * R.N.Shorten, D.J.Leith:
 *   "H-TCP: TCP for high-speed and long-distance networks"
 *   Proc. PFLDnet, Argonne, 2004.
 * https://www.hamilton.ie/net/htcp3.pdf
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <net/tcp.h>

#define ALPHA_BASE	(1<<7)	/* 1.0 with shift << 7 */
#define BETA_MIN	(1<<6)	/* 0.5 with shift << 7 */
#define BETA_MAX	102	/* 0.8 with shift << 7 */

static int use_rtt_scaling __read_mostly = 1;
module_param(use_rtt_scaling, int, 0644);
MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");

static int use_bandwidth_switch __read_mostly = 1;
module_param(use_bandwidth_switch, int, 0644);
MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");

struct htcp {
	u32	alpha;		/* Fixed point arith, << 7 */
	u8	beta;           /* Fixed point arith, << 7 */
	u8	modeswitch;	/* Delay modeswitch
				   until we had at least one congestion event */
	u16	pkts_acked;
	u32	packetcount;
	u32	minRTT;
	u32	maxRTT;
	u32	last_cong;	/* Time since last congestion event end */
	u32	undo_last_cong;

	u32	undo_maxRTT;
	u32	undo_old_maxB;

	/* Bandwidth estimation */
	u32	minB;
	u32	maxB;
	u32	old_maxB;
	u32	Bi;
	u32	lasttime;
};

static inline u32 htcp_cong_time(const struct htcp *ca)
{
	return jiffies - ca->last_cong;
}

static inline u32 htcp_ccount(const struct htcp *ca)
{
	return htcp_cong_time(ca) / ca->minRTT;
}

static inline void htcp_reset(struct htcp *ca)
{
	ca->undo_last_cong = ca->last_cong;
	ca->undo_maxRTT = ca->maxRTT;
	ca->undo_old_maxB = ca->old_maxB;

	ca->last_cong = jiffies;
}

static u32 htcp_cwnd_undo(struct sock *sk)
{
	struct htcp *ca = inet_csk_ca(sk);

	if (ca->undo_last_cong) {
		ca->last_cong = ca->undo_last_cong;
		ca->maxRTT = ca->undo_maxRTT;
		ca->old_maxB = ca->undo_old_maxB;
		ca->undo_last_cong = 0;
	}

	return tcp_reno_undo_cwnd(sk);
}

static inline void measure_rtt(struct sock *sk, u32 srtt)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct htcp *ca = inet_csk_ca(sk);

	/* keep track of minimum RTT seen so far, minRTT is zero at first */
	if (ca->minRTT > srtt || !ca->minRTT)
		ca->minRTT = srtt;

	/* max RTT */
	if (icsk->icsk_ca_state == TCP_CA_Open) {
		if (ca->maxRTT < ca->minRTT)
			ca->maxRTT = ca->minRTT;
		if (ca->maxRTT < srtt &&
		    srtt <= ca->maxRTT + msecs_to_jiffies(20))
			ca->maxRTT = srtt;
	}
}

static void measure_achieved_throughput(struct sock *sk,
					const struct ack_sample *sample)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	const struct tcp_sock *tp = tcp_sk(sk);
	struct htcp *ca = inet_csk_ca(sk);
	u32 now = tcp_jiffies32;

	if (icsk->icsk_ca_state == TCP_CA_Open)
		ca->pkts_acked = sample->pkts_acked;

	if (sample->rtt_us > 0)
		measure_rtt(sk, usecs_to_jiffies(sample->rtt_us));

	if (!use_bandwidth_switch)
		return;

	/* achieved throughput calculations */
	if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) {
		ca->packetcount = 0;
		ca->lasttime = now;
		return;
	}

	ca->packetcount += sample->pkts_acked;

	if (ca->packetcount >= tp->snd_cwnd - (ca->alpha >> 7 ? : 1) &&
	    now - ca->lasttime >= ca->minRTT &&
	    ca->minRTT > 0) {
		__u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);

		if (htcp_ccount(ca) <= 3) {
			/* just after backoff */
			ca->minB = ca->maxB = ca->Bi = cur_Bi;
		} else {
			ca->Bi = (3 * ca->Bi + cur_Bi) / 4;
			if (ca->Bi > ca->maxB)
				ca->maxB = ca->Bi;
			if (ca->minB > ca->maxB)
				ca->minB = ca->maxB;
		}
		ca->packetcount = 0;
		ca->lasttime = now;
	}
}

static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
{
	if (use_bandwidth_switch) {
		u32 maxB = ca->maxB;
		u32 old_maxB = ca->old_maxB;

		ca->old_maxB = ca->maxB;
		if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) {
			ca->beta = BETA_MIN;
			ca->modeswitch = 0;
			return;
		}
	}

	if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
		ca->beta = (minRTT << 7) / maxRTT;
		if (ca->beta < BETA_MIN)
			ca->beta = BETA_MIN;
		else if (ca->beta > BETA_MAX)
			ca->beta = BETA_MAX;
	} else {
		ca->beta = BETA_MIN;
		ca->modeswitch = 1;
	}
}

static inline void htcp_alpha_update(struct htcp *ca)
{
	u32 minRTT = ca->minRTT;
	u32 factor = 1;
	u32 diff = htcp_cong_time(ca);

	if (diff > HZ) {
		diff -= HZ;
		factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ;
	}

	if (use_rtt_scaling && minRTT) {
		u32 scale = (HZ << 3) / (10 * minRTT);

		/* clamping ratio to interval [0.5,10]<<3 */
		scale = min(max(scale, 1U << 2), 10U << 3);
		factor = (factor << 3) / scale;
		if (!factor)
			factor = 1;
	}

	ca->alpha = 2 * factor * ((1 << 7) - ca->beta);
	if (!ca->alpha)
		ca->alpha = ALPHA_BASE;
}

/*
 * After we have the rtt data to calculate beta, we'd still prefer to wait one
 * rtt before we adjust our beta to ensure we are working from a consistent
 * data.
 *
 * This function should be called when we hit a congestion event since only at
 * that point do we really have a real sense of maxRTT (the queues en route
 * were getting just too full now).
 */
static void htcp_param_update(struct sock *sk)
{
	struct htcp *ca = inet_csk_ca(sk);
	u32 minRTT = ca->minRTT;
	u32 maxRTT = ca->maxRTT;

	htcp_beta_update(ca, minRTT, maxRTT);
	htcp_alpha_update(ca);

	/* add slowly fading memory for maxRTT to accommodate routing changes */
	if (minRTT > 0 && maxRTT > minRTT)
		ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100;
}

static u32 htcp_recalc_ssthresh(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct htcp *ca = inet_csk_ca(sk);

	htcp_param_update(sk);
	return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
}

static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct htcp *ca = inet_csk_ca(sk);

	if (!tcp_is_cwnd_limited(sk))
		return;

	if (tcp_in_slow_start(tp))
		tcp_slow_start(tp, acked);
	else {
		/* In dangerous area, increase slowly.
		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
		 */
		if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
				tp->snd_cwnd++;
			tp->snd_cwnd_cnt = 0;
			htcp_alpha_update(ca);
		} else
			tp->snd_cwnd_cnt += ca->pkts_acked;

		ca->pkts_acked = 1;
	}
}

static void htcp_init(struct sock *sk)
{
	struct htcp *ca = inet_csk_ca(sk);

	memset(ca, 0, sizeof(struct htcp));
	ca->alpha = ALPHA_BASE;
	ca->beta = BETA_MIN;
	ca->pkts_acked = 1;
	ca->last_cong = jiffies;
}

static void htcp_state(struct sock *sk, u8 new_state)
{
	switch (new_state) {
	case TCP_CA_Open:
		{
			struct htcp *ca = inet_csk_ca(sk);

			if (ca->undo_last_cong) {
				ca->last_cong = jiffies;
				ca->undo_last_cong = 0;
			}
		}
		break;
	case TCP_CA_CWR:
	case TCP_CA_Recovery:
	case TCP_CA_Loss:
		htcp_reset(inet_csk_ca(sk));
		break;
	}
}

static struct tcp_congestion_ops htcp __read_mostly = {
	.init		= htcp_init,
	.ssthresh	= htcp_recalc_ssthresh,
	.cong_avoid	= htcp_cong_avoid,
	.set_state	= htcp_state,
	.undo_cwnd	= htcp_cwnd_undo,
	.pkts_acked	= measure_achieved_throughput,
	.owner		= THIS_MODULE,
	.name		= "htcp",
};

static int __init htcp_register(void)
{
	BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
	BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
	return tcp_register_congestion_control(&htcp);
}

static void __exit htcp_unregister(void)
{
	tcp_unregister_congestion_control(&htcp);
}

module_init(htcp_register);
module_exit(htcp_unregister);

MODULE_AUTHOR("Baruch Even");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("H-TCP");