summaryrefslogtreecommitdiffstats
path: root/net/ipv4/tcp_lp.c
blob: d6fb6c067af4641f232b94e7c590c212648e8173 (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
332
333
334
335
336
337
338
339
340
341
342
343
344
345
/*
 * TCP Low Priority (TCP-LP)
 *
 * TCP Low Priority is a distributed algorithm whose goal is to utilize only
 *   the excess network bandwidth as compared to the ``fair share`` of
 *   bandwidth as targeted by TCP.
 *
 * As of 2.6.13, Linux supports pluggable congestion control algorithms.
 * Due to the limitation of the API, we take the following changes from
 * the original TCP-LP implementation:
 *   o We use newReno in most core CA handling. Only add some checking
 *     within cong_avoid.
 *   o Error correcting in remote HZ, therefore remote HZ will be keeped
 *     on checking and updating.
 *   o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
 *     OWD have a similar meaning as RTT. Also correct the buggy formular.
 *   o Handle reaction for Early Congestion Indication (ECI) within
 *     pkts_acked, as mentioned within pseudo code.
 *   o OWD is handled in relative format, where local time stamp will in
 *     tcp_time_stamp format.
 *
 * Original Author:
 *   Aleksandar Kuzmanovic <akuzma@northwestern.edu>
 * Available from:
 *   http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
 * Original implementation for 2.4.19:
 *   http://www-ece.rice.edu/networks/TCP-LP/
 *
 * 2.6.x module Authors:
 *   Wong Hoi Sing, Edison <hswong3i@gmail.com>
 *   Hung Hing Lun, Mike <hlhung3i@gmail.com>
 * SourceForge project page:
 *   http://tcp-lp-mod.sourceforge.net/
 */

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

/* resolution of owd */
#define LP_RESOL       1000

/**
 * enum tcp_lp_state
 * @LP_VALID_RHZ: is remote HZ valid?
 * @LP_VALID_OWD: is OWD valid?
 * @LP_WITHIN_THR: are we within threshold?
 * @LP_WITHIN_INF: are we within inference?
 *
 * TCP-LP's state flags.
 * We create this set of state flag mainly for debugging.
 */
enum tcp_lp_state {
	LP_VALID_RHZ = (1 << 0),
	LP_VALID_OWD = (1 << 1),
	LP_WITHIN_THR = (1 << 3),
	LP_WITHIN_INF = (1 << 4),
};

/**
 * struct lp
 * @flag: TCP-LP state flag
 * @sowd: smoothed OWD << 3
 * @owd_min: min OWD
 * @owd_max: max OWD
 * @owd_max_rsv: resrved max owd
 * @remote_hz: estimated remote HZ
 * @remote_ref_time: remote reference time
 * @local_ref_time: local reference time
 * @last_drop: time for last active drop
 * @inference: current inference
 *
 * TCP-LP's private struct.
 * We get the idea from original TCP-LP implementation where only left those we
 * found are really useful.
 */
struct lp {
	u32 flag;
	u32 sowd;
	u32 owd_min;
	u32 owd_max;
	u32 owd_max_rsv;
	u32 remote_hz;
	u32 remote_ref_time;
	u32 local_ref_time;
	u32 last_drop;
	u32 inference;
};

/**
 * tcp_lp_init
 *
 * Init all required variables.
 * Clone the handling from Vegas module implementation.
 */
static void tcp_lp_init(struct sock *sk)
{
	struct lp *lp = inet_csk_ca(sk);

	lp->flag = 0;
	lp->sowd = 0;
	lp->owd_min = 0xffffffff;
	lp->owd_max = 0;
	lp->owd_max_rsv = 0;
	lp->remote_hz = 0;
	lp->remote_ref_time = 0;
	lp->local_ref_time = 0;
	lp->last_drop = 0;
	lp->inference = 0;
}

/**
 * tcp_lp_cong_avoid
 *
 * Implementation of cong_avoid.
 * Will only call newReno CA when away from inference.
 * From TCP-LP's paper, this will be handled in additive increasement.
 */
static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
	struct lp *lp = inet_csk_ca(sk);

	if (!(lp->flag & LP_WITHIN_INF))
		tcp_reno_cong_avoid(sk, ack, acked);
}

/**
 * tcp_lp_remote_hz_estimator
 *
 * Estimate remote HZ.
 * We keep on updating the estimated value, where original TCP-LP
 * implementation only guest it for once and use forever.
 */
static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	s64 rhz = lp->remote_hz << 6;	/* remote HZ << 6 */
	s64 m = 0;

	/* not yet record reference time
	 * go away!! record it before come back!! */
	if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
		goto out;

	/* we can't calc remote HZ with no different!! */
	if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
	    tp->rx_opt.rcv_tsecr == lp->local_ref_time)
		goto out;

	m = HZ * (tp->rx_opt.rcv_tsval -
		  lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr -
					  lp->local_ref_time);
	if (m < 0)
		m = -m;

	if (rhz > 0) {
		m -= rhz >> 6;	/* m is now error in remote HZ est */
		rhz += m;	/* 63/64 old + 1/64 new */
	} else
		rhz = m << 6;

 out:
	/* record time for successful remote HZ calc */
	if ((rhz >> 6) > 0)
		lp->flag |= LP_VALID_RHZ;
	else
		lp->flag &= ~LP_VALID_RHZ;

	/* record reference time stamp */
	lp->remote_ref_time = tp->rx_opt.rcv_tsval;
	lp->local_ref_time = tp->rx_opt.rcv_tsecr;

	return rhz >> 6;
}

/**
 * tcp_lp_owd_calculator
 *
 * Calculate one way delay (in relative format).
 * Original implement OWD as minus of remote time difference to local time
 * difference directly. As this time difference just simply equal to RTT, when
 * the network status is stable, remote RTT will equal to local RTT, and result
 * OWD into zero.
 * It seems to be a bug and so we fixed it.
 */
static u32 tcp_lp_owd_calculator(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	s64 owd = 0;

	lp->remote_hz = tcp_lp_remote_hz_estimator(sk);

	if (lp->flag & LP_VALID_RHZ) {
		owd =
		    tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
		    tp->rx_opt.rcv_tsecr * (LP_RESOL / HZ);
		if (owd < 0)
			owd = -owd;
	}

	if (owd > 0)
		lp->flag |= LP_VALID_OWD;
	else
		lp->flag &= ~LP_VALID_OWD;

	return owd;
}

/**
 * tcp_lp_rtt_sample
 *
 * Implementation or rtt_sample.
 * Will take the following action,
 *   1. calc OWD,
 *   2. record the min/max OWD,
 *   3. calc smoothed OWD (SOWD).
 * Most ideas come from the original TCP-LP implementation.
 */
static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
{
	struct lp *lp = inet_csk_ca(sk);
	s64 mowd = tcp_lp_owd_calculator(sk);

	/* sorry that we don't have valid data */
	if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
		return;

	/* record the next min owd */
	if (mowd < lp->owd_min)
		lp->owd_min = mowd;

	/* always forget the max of the max
	 * we just set owd_max as one below it */
	if (mowd > lp->owd_max) {
		if (mowd > lp->owd_max_rsv) {
			if (lp->owd_max_rsv == 0)
				lp->owd_max = mowd;
			else
				lp->owd_max = lp->owd_max_rsv;
			lp->owd_max_rsv = mowd;
		} else
			lp->owd_max = mowd;
	}

	/* calc for smoothed owd */
	if (lp->sowd != 0) {
		mowd -= lp->sowd >> 3;	/* m is now error in owd est */
		lp->sowd += mowd;	/* owd = 7/8 owd + 1/8 new */
	} else
		lp->sowd = mowd << 3;	/* take the measured time be owd */
}

/**
 * tcp_lp_pkts_acked
 *
 * Implementation of pkts_acked.
 * Deal with active drop under Early Congestion Indication.
 * Only drop to half and 1 will be handle, because we hope to use back
 * newReno in increase case.
 * We work it out by following the idea from TCP-LP's paper directly
 */
static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct lp *lp = inet_csk_ca(sk);
	u32 delta;

	if (sample->rtt_us > 0)
		tcp_lp_rtt_sample(sk, sample->rtt_us);

	/* calc inference */
	delta = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
	if ((s32)delta > 0)
		lp->inference = 3 * delta;

	/* test if within inference */
	if (lp->last_drop && (tcp_time_stamp - lp->last_drop < lp->inference))
		lp->flag |= LP_WITHIN_INF;
	else
		lp->flag &= ~LP_WITHIN_INF;

	/* test if within threshold */
	if (lp->sowd >> 3 <
	    lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
		lp->flag |= LP_WITHIN_THR;
	else
		lp->flag &= ~LP_WITHIN_THR;

	pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
		 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
		 lp->sowd >> 3);

	if (lp->flag & LP_WITHIN_THR)
		return;

	/* FIXME: try to reset owd_min and owd_max here
	 * so decrease the chance the min/max is no longer suitable
	 * and will usually within threshold when whithin inference */
	lp->owd_min = lp->sowd >> 3;
	lp->owd_max = lp->sowd >> 2;
	lp->owd_max_rsv = lp->sowd >> 2;

	/* happened within inference
	 * drop snd_cwnd into 1 */
	if (lp->flag & LP_WITHIN_INF)
		tp->snd_cwnd = 1U;

	/* happened after inference
	 * cut snd_cwnd into half */
	else
		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);

	/* record this drop time */
	lp->last_drop = tcp_time_stamp;
}

static struct tcp_congestion_ops tcp_lp __read_mostly = {
	.init = tcp_lp_init,
	.ssthresh = tcp_reno_ssthresh,
	.undo_cwnd = tcp_reno_undo_cwnd,
	.cong_avoid = tcp_lp_cong_avoid,
	.pkts_acked = tcp_lp_pkts_acked,

	.owner = THIS_MODULE,
	.name = "lp"
};

static int __init tcp_lp_register(void)
{
	BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
	return tcp_register_congestion_control(&tcp_lp);
}

static void __exit tcp_lp_unregister(void)
{
	tcp_unregister_congestion_control(&tcp_lp);
}

module_init(tcp_lp_register);
module_exit(tcp_lp_unregister);

MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Low Priority");