summaryrefslogtreecommitdiffstats
path: root/net/ipv4/tcp_bic.c
blob: ec38d45d6649633178c8d541a34499349443c8a4 (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
318
319
320
321
322
323
324
325
326
327
328
329
330
331
/*
 * Binary Increase Congestion control for TCP
 *
 * This is from the implementation of BICTCP in
 * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
 *  "Binary Increase Congestion Control for Fast, Long Distance
 *  Networks" in InfoComm 2004
 * Available from:
 *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
 *
 * Unless BIC is enabled and congestion window is large
 * this behaves the same as the original Reno.
 */

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


#define BICTCP_BETA_SCALE    1024	/* Scale factor beta calculation
					 * max_cwnd = snd_cwnd * beta
					 */
#define BICTCP_B		4	 /*
					  * In binary search,
					  * go to point (max+min)/N
					  */

static int fast_convergence = 1;
static int max_increment = 32;
static int low_window = 14;
static int beta = 819;		/* = 819/1024 (BICTCP_BETA_SCALE) */
static int low_utilization_threshold = 153;
static int low_utilization_period = 2;
static int initial_ssthresh = 100;
static int smooth_part = 20;

module_param(fast_convergence, int, 0644);
MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
module_param(max_increment, int, 0644);
MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
module_param(low_window, int, 0644);
MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
module_param(beta, int, 0644);
MODULE_PARM_DESC(beta, "beta for multiplicative increase");
module_param(low_utilization_threshold, int, 0644);
MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
module_param(low_utilization_period, int, 0644);
MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
module_param(initial_ssthresh, int, 0644);
MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
module_param(smooth_part, int, 0644);
MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");


/* BIC TCP Parameters */
struct bictcp {
	u32	cnt;		/* increase cwnd by 1 after ACKs */
	u32 	last_max_cwnd;	/* last maximum snd_cwnd */
	u32	loss_cwnd;	/* congestion window at last loss */
	u32	last_cwnd;	/* the last snd_cwnd */
	u32	last_time;	/* time when updated last_cwnd */
	u32	delay_min;	/* min delay */
	u32	delay_max;	/* max delay */
	u32	last_delay;
	u8	low_utilization;/* 0: high; 1: low */
	u32	low_utilization_start;	/* starting time of low utilization detection*/
	u32	epoch_start;	/* beginning of an epoch */
#define ACK_RATIO_SHIFT	4
	u32	delayed_ack;	/* estimate the ratio of Packets/ACKs << 4 */
};

static inline void bictcp_reset(struct bictcp *ca)
{
	ca->cnt = 0;
	ca->last_max_cwnd = 0;
	ca->loss_cwnd = 0;
	ca->last_cwnd = 0;
	ca->last_time = 0;
	ca->delay_min = 0;
	ca->delay_max = 0;
	ca->last_delay = 0;
	ca->low_utilization = 0;
	ca->low_utilization_start = 0;
	ca->epoch_start = 0;
	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
}

static void bictcp_init(struct tcp_sock *tp)
{
	bictcp_reset(tcp_ca(tp));
	if (initial_ssthresh)
		tp->snd_ssthresh = initial_ssthresh;
}

/*
 * Compute congestion window to use.
 */
static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
{
	if (ca->last_cwnd == cwnd &&
	    (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
		return;

	ca->last_cwnd = cwnd;
	ca->last_time = tcp_time_stamp;

	if (ca->epoch_start == 0) /* record the beginning of an epoch */
		ca->epoch_start = tcp_time_stamp;

	/* start off normal */
	if (cwnd <= low_window) {
		ca->cnt = cwnd;
		return;
	}

	/* binary increase */
	if (cwnd < ca->last_max_cwnd) {
		__u32 	dist = (ca->last_max_cwnd - cwnd)
			/ BICTCP_B;

		if (dist > max_increment)
			/* linear increase */
			ca->cnt = cwnd / max_increment;
		else if (dist <= 1U)
			/* binary search increase */
			ca->cnt = (cwnd * smooth_part) / BICTCP_B;
		else
			/* binary search increase */
			ca->cnt = cwnd / dist;
	} else {
		/* slow start AMD linear increase */
		if (cwnd < ca->last_max_cwnd + BICTCP_B)
			/* slow start */
			ca->cnt = (cwnd * smooth_part) / BICTCP_B;
		else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
			/* slow start */
			ca->cnt = (cwnd * (BICTCP_B-1))
				/ cwnd-ca->last_max_cwnd;
		else
			/* linear increase */
			ca->cnt = cwnd / max_increment;
	}

	/* if in slow start or link utilization is very low */
	if ( ca->loss_cwnd == 0 ||
	     (cwnd > ca->loss_cwnd && ca->low_utilization)) {
		if (ca->cnt > 20) /* increase cwnd 5% per RTT */
			ca->cnt = 20;
	}

	ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
	if (ca->cnt == 0)			/* cannot be zero */
		ca->cnt = 1;
}


/* Detect low utilization in congestion avoidance */
static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
{
	struct bictcp *ca = tcp_ca(tp);
	u32 dist, delay;

	/* No time stamp */
	if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
	     /* Discard delay samples right after fast recovery */
	     tcp_time_stamp < ca->epoch_start + HZ ||
	     /* this delay samples may not be accurate */
	     flag == 0) {
		ca->last_delay = 0;
		goto notlow;
	}

	delay = ca->last_delay<<3;	/* use the same scale as tp->srtt*/
	ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
	if (delay == 0) 		/* no previous delay sample */
		goto notlow;

	/* first time call or link delay decreases */
	if (ca->delay_min == 0 || ca->delay_min > delay) {
		ca->delay_min = ca->delay_max = delay;
		goto notlow;
	}

	if (ca->delay_max < delay)
		ca->delay_max = delay;

	/* utilization is low, if avg delay < dist*threshold
	   for checking_period time */
	dist = ca->delay_max - ca->delay_min;
	if (dist <= ca->delay_min>>6 ||
	    tp->srtt - ca->delay_min >=  (dist*low_utilization_threshold)>>10)
		goto notlow;

	if (ca->low_utilization_start == 0) {
		ca->low_utilization = 0;
		ca->low_utilization_start = tcp_time_stamp;
	} else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
			> low_utilization_period*HZ) {
		ca->low_utilization = 1;
	}

	return;

 notlow:
	ca->low_utilization = 0;
	ca->low_utilization_start = 0;

}

static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
			      u32 seq_rtt, u32 in_flight, int data_acked)
{
	struct bictcp *ca = tcp_ca(tp);

	bictcp_low_utilization(tp, data_acked);

	if (in_flight < tp->snd_cwnd)
		return;

	if (tp->snd_cwnd <= tp->snd_ssthresh) {
		/* In "safe" area, increase. */
		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
			tp->snd_cwnd++;
	} else {
		bictcp_update(ca, tp->snd_cwnd);

                /* In dangerous area, increase slowly.
		 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
		 */
		if (tp->snd_cwnd_cnt >= ca->cnt) {
			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
				tp->snd_cwnd++;
			tp->snd_cwnd_cnt = 0;
		} else
			tp->snd_cwnd_cnt++;
	}

}

/*
 *	behave like Reno until low_window is reached,
 *	then increase congestion window slowly
 */
static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
{
	struct bictcp *ca = tcp_ca(tp);

	ca->epoch_start = 0;	/* end of epoch */

	/* in case of wrong delay_max*/
	if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
		ca->delay_max = ca->delay_min
			+ ((ca->delay_max - ca->delay_min)* 90) / 100;

	/* Wmax and fast convergence */
	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
		ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
			/ (2 * BICTCP_BETA_SCALE);
	else
		ca->last_max_cwnd = tp->snd_cwnd;

	ca->loss_cwnd = tp->snd_cwnd;


	if (tp->snd_cwnd <= low_window)
		return max(tp->snd_cwnd >> 1U, 2U);
	else
		return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
}

static u32 bictcp_undo_cwnd(struct tcp_sock *tp)
{
	struct bictcp *ca = tcp_ca(tp);

	return max(tp->snd_cwnd, ca->last_max_cwnd);
}

static u32 bictcp_min_cwnd(struct tcp_sock *tp)
{
	return tp->snd_ssthresh;
}

static void bictcp_state(struct tcp_sock *tp, u8 new_state)
{
	if (new_state == TCP_CA_Loss)
		bictcp_reset(tcp_ca(tp));
}

/* Track delayed acknowledgement ratio using sliding window
 * ratio = (15*ratio + sample) / 16
 */
static void bictcp_acked(struct tcp_sock *tp, u32 cnt)
{
	if (cnt > 0 && 	tp->ca_state == TCP_CA_Open) {
		struct bictcp *ca = tcp_ca(tp);
		cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
		ca->delayed_ack += cnt;
	}
}


static struct tcp_congestion_ops bictcp = {
	.init		= bictcp_init,
	.ssthresh	= bictcp_recalc_ssthresh,
	.cong_avoid	= bictcp_cong_avoid,
	.set_state	= bictcp_state,
	.undo_cwnd	= bictcp_undo_cwnd,
	.min_cwnd	= bictcp_min_cwnd,
	.pkts_acked     = bictcp_acked,
	.owner		= THIS_MODULE,
	.name		= "bic",
};

static int __init bictcp_register(void)
{
	BUG_ON(sizeof(struct bictcp) > TCP_CA_PRIV_SIZE);
	return tcp_register_congestion_control(&bictcp);
}

static void __exit bictcp_unregister(void)
{
	tcp_unregister_congestion_control(&bictcp);
}

module_init(bictcp_register);
module_exit(bictcp_unregister);

MODULE_AUTHOR("Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("BIC TCP");
OpenPOWER on IntegriCloud