1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * TCP Low Priority (TCP-LP)
4 *
5 * TCP Low Priority is a distributed algorithm whose goal is to utilize only
6 * the excess network bandwidth as compared to the ``fair share`` of
7 * bandwidth as targeted by TCP.
8 *
9 * As of 2.6.13, Linux supports pluggable congestion control algorithms.
10 * Due to the limitation of the API, we take the following changes from
11 * the original TCP-LP implementation:
12 * o We use newReno in most core CA handling. Only add some checking
13 * within cong_avoid.
14 * o Error correcting in remote HZ, therefore remote HZ will be keeped
15 * on checking and updating.
16 * o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
17 * OWD have a similar meaning as RTT. Also correct the buggy formular.
18 * o Handle reaction for Early Congestion Indication (ECI) within
19 * pkts_acked, as mentioned within pseudo code.
20 * o OWD is handled in relative format, where local time stamp will in
21 * tcp_time_stamp format.
22 *
23 * Original Author:
24 * Aleksandar Kuzmanovic <akuzma@northwestern.edu>
25 * Available from:
26 * http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
27 * Original implementation for 2.4.19:
28 * http://www-ece.rice.edu/networks/TCP-LP/
29 *
30 * 2.6.x module Authors:
31 * Wong Hoi Sing, Edison <hswong3i@gmail.com>
32 * Hung Hing Lun, Mike <hlhung3i@gmail.com>
33 * SourceForge project page:
34 * http://tcp-lp-mod.sourceforge.net/
35 */
36
37 #include <linux/module.h>
38 #include <net/tcp.h>
39
40 /* resolution of owd */
41 #define LP_RESOL TCP_TS_HZ
42
43 /**
44 * enum tcp_lp_state
45 * @LP_VALID_RHZ: is remote HZ valid?
46 * @LP_VALID_OWD: is OWD valid?
47 * @LP_WITHIN_THR: are we within threshold?
48 * @LP_WITHIN_INF: are we within inference?
49 *
50 * TCP-LP's state flags.
51 * We create this set of state flag mainly for debugging.
52 */
53 enum tcp_lp_state {
54 LP_VALID_RHZ = (1 << 0),
55 LP_VALID_OWD = (1 << 1),
56 LP_WITHIN_THR = (1 << 3),
57 LP_WITHIN_INF = (1 << 4),
58 };
59
60 /**
61 * struct lp
62 * @flag: TCP-LP state flag
63 * @sowd: smoothed OWD << 3
64 * @owd_min: min OWD
65 * @owd_max: max OWD
66 * @owd_max_rsv: reserved max owd
67 * @remote_hz: estimated remote HZ
68 * @remote_ref_time: remote reference time
69 * @local_ref_time: local reference time
70 * @last_drop: time for last active drop
71 * @inference: current inference
72 *
73 * TCP-LP's private struct.
74 * We get the idea from original TCP-LP implementation where only left those we
75 * found are really useful.
76 */
77 struct lp {
78 u32 flag;
79 u32 sowd;
80 u32 owd_min;
81 u32 owd_max;
82 u32 owd_max_rsv;
83 u32 remote_hz;
84 u32 remote_ref_time;
85 u32 local_ref_time;
86 u32 last_drop;
87 u32 inference;
88 };
89
90 /**
91 * tcp_lp_init
92 * @sk: socket to initialize congestion control algorithm for
93 *
94 * Init all required variables.
95 * Clone the handling from Vegas module implementation.
96 */
97 static void tcp_lp_init(struct sock *sk)
98 {
99 struct lp *lp = inet_csk_ca(sk);
100
101 lp->flag = 0;
102 lp->sowd = 0;
103 lp->owd_min = 0xffffffff;
104 lp->owd_max = 0;
105 lp->owd_max_rsv = 0;
106 lp->remote_hz = 0;
107 lp->remote_ref_time = 0;
108 lp->local_ref_time = 0;
109 lp->last_drop = 0;
110 lp->inference = 0;
111 }
112
113 /**
114 * tcp_lp_cong_avoid
115 * @sk: socket to avoid congesting
116 *
117 * Implementation of cong_avoid.
118 * Will only call newReno CA when away from inference.
119 * From TCP-LP's paper, this will be handled in additive increasement.
120 */
121 static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
122 {
123 struct lp *lp = inet_csk_ca(sk);
124
125 if (!(lp->flag & LP_WITHIN_INF))
126 tcp_reno_cong_avoid(sk, ack, acked);
127 }
128
129 /**
130 * tcp_lp_remote_hz_estimator
131 * @sk: socket which needs an estimate for the remote HZs
132 *
133 * Estimate remote HZ.
134 * We keep on updating the estimated value, where original TCP-LP
135 * implementation only guest it for once and use forever.
136 */
137 static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
138 {
139 struct tcp_sock *tp = tcp_sk(sk);
140 struct lp *lp = inet_csk_ca(sk);
141 s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */
142 s64 m = 0;
143
144 /* not yet record reference time
145 * go away!! record it before come back!! */
146 if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
147 goto out;
148
149 /* we can't calc remote HZ with no different!! */
150 if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
151 tp->rx_opt.rcv_tsecr == lp->local_ref_time)
152 goto out;
153
154 m = TCP_TS_HZ *
155 (tp->rx_opt.rcv_tsval - lp->remote_ref_time) /
156 (tp->rx_opt.rcv_tsecr - lp->local_ref_time);
157 if (m < 0)
158 m = -m;
159
160 if (rhz > 0) {
161 m -= rhz >> 6; /* m is now error in remote HZ est */
162 rhz += m; /* 63/64 old + 1/64 new */
163 } else
164 rhz = m << 6;
165
166 out:
167 /* record time for successful remote HZ calc */
168 if ((rhz >> 6) > 0)
169 lp->flag |= LP_VALID_RHZ;
170 else
171 lp->flag &= ~LP_VALID_RHZ;
172
173 /* record reference time stamp */
174 lp->remote_ref_time = tp->rx_opt.rcv_tsval;
175 lp->local_ref_time = tp->rx_opt.rcv_tsecr;
176
177 return rhz >> 6;
178 }
179
180 /**
181 * tcp_lp_owd_calculator
182 * @sk: socket to calculate one way delay for
183 *
184 * Calculate one way delay (in relative format).
185 * Original implement OWD as minus of remote time difference to local time
186 * difference directly. As this time difference just simply equal to RTT, when
187 * the network status is stable, remote RTT will equal to local RTT, and result
188 * OWD into zero.
189 * It seems to be a bug and so we fixed it.
190 */
191 static u32 tcp_lp_owd_calculator(struct sock *sk)
192 {
193 struct tcp_sock *tp = tcp_sk(sk);
194 struct lp *lp = inet_csk_ca(sk);
195 s64 owd = 0;
196
197 lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
198
199 if (lp->flag & LP_VALID_RHZ) {
200 owd =
201 tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
202 tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ);
203 if (owd < 0)
204 owd = -owd;
205 }
206
207 if (owd > 0)
208 lp->flag |= LP_VALID_OWD;
209 else
210 lp->flag &= ~LP_VALID_OWD;
211
212 return owd;
213 }
214
215 /**
216 * tcp_lp_rtt_sample
217 * @sk: socket to add a rtt sample to
218 * @rtt: round trip time, which is ignored!
219 *
220 * Implementation or rtt_sample.
221 * Will take the following action,
222 * 1. calc OWD,
223 * 2. record the min/max OWD,
224 * 3. calc smoothed OWD (SOWD).
225 * Most ideas come from the original TCP-LP implementation.
226 */
227 static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
228 {
229 struct lp *lp = inet_csk_ca(sk);
230 s64 mowd = tcp_lp_owd_calculator(sk);
231
232 /* sorry that we don't have valid data */
233 if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
234 return;
235
236 /* record the next min owd */
237 if (mowd < lp->owd_min)
238 lp->owd_min = mowd;
239
240 /* always forget the max of the max
241 * we just set owd_max as one below it */
242 if (mowd > lp->owd_max) {
243 if (mowd > lp->owd_max_rsv) {
244 if (lp->owd_max_rsv == 0)
245 lp->owd_max = mowd;
246 else
247 lp->owd_max = lp->owd_max_rsv;
248 lp->owd_max_rsv = mowd;
249 } else
250 lp->owd_max = mowd;
251 }
252
253 /* calc for smoothed owd */
254 if (lp->sowd != 0) {
255 mowd -= lp->sowd >> 3; /* m is now error in owd est */
256 lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */
257 } else
258 lp->sowd = mowd << 3; /* take the measured time be owd */
259 }
260
261 /**
262 * tcp_lp_pkts_acked
263 * @sk: socket requiring congestion avoidance calculations
264 *
265 * Implementation of pkts_acked.
266 * Deal with active drop under Early Congestion Indication.
267 * Only drop to half and 1 will be handle, because we hope to use back
268 * newReno in increase case.
269 * We work it out by following the idea from TCP-LP's paper directly
270 */
271 static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
272 {
273 struct tcp_sock *tp = tcp_sk(sk);
274 struct lp *lp = inet_csk_ca(sk);
275 u32 now = tcp_time_stamp_ts(tp);
276 u32 delta;
277
278 if (sample->rtt_us > 0)
279 tcp_lp_rtt_sample(sk, sample->rtt_us);
280
281 /* calc inference */
282 delta = now - tp->rx_opt.rcv_tsecr;
283 if ((s32)delta > 0)
284 lp->inference = 3 * delta;
285
286 /* test if within inference */
287 if (lp->last_drop && (now - lp->last_drop < lp->inference))
288 lp->flag |= LP_WITHIN_INF;
289 else
290 lp->flag &= ~LP_WITHIN_INF;
291
292 /* test if within threshold */
293 if (lp->sowd >> 3 <
294 lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
295 lp->flag |= LP_WITHIN_THR;
296 else
297 lp->flag &= ~LP_WITHIN_THR;
298
299 pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
300 tcp_snd_cwnd(tp), lp->remote_hz, lp->owd_min, lp->owd_max,
301 lp->sowd >> 3);
302
303 if (lp->flag & LP_WITHIN_THR)
304 return;
305
306 /* FIXME: try to reset owd_min and owd_max here
307 * so decrease the chance the min/max is no longer suitable
308 * and will usually within threshold when within inference */
309 lp->owd_min = lp->sowd >> 3;
310 lp->owd_max = lp->sowd >> 2;
311 lp->owd_max_rsv = lp->sowd >> 2;
312
313 /* happened within inference
314 * drop snd_cwnd into 1 */
315 if (lp->flag & LP_WITHIN_INF)
316 tcp_snd_cwnd_set(tp, 1U);
317
318 /* happened after inference
319 * cut snd_cwnd into half */
320 else
321 tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp) >> 1U, 1U));
322
323 /* record this drop time */
324 lp->last_drop = now;
325 }
326
327 static struct tcp_congestion_ops tcp_lp __read_mostly = {
328 .init = tcp_lp_init,
329 .ssthresh = tcp_reno_ssthresh,
330 .undo_cwnd = tcp_reno_undo_cwnd,
331 .cong_avoid = tcp_lp_cong_avoid,
332 .pkts_acked = tcp_lp_pkts_acked,
333
334 .owner = THIS_MODULE,
335 .name = "lp"
336 };
337
338 static int __init tcp_lp_register(void)
339 {
340 BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
341 return tcp_register_congestion_control(&tcp_lp);
342 }
343
344 static void __exit tcp_lp_unregister(void)
345 {
346 tcp_unregister_congestion_control(&tcp_lp);
347 }
348
349 module_init(tcp_lp_register);
350 module_exit(tcp_lp_unregister);
351
352 MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
353 MODULE_LICENSE("GPL");
354 MODULE_DESCRIPTION("TCP Low Priority");
355
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