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, rtt: 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, val: 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(type: &tcp_lp); |
342 | } |
343 | |
344 | static void __exit tcp_lp_unregister(void) |
345 | { |
346 | tcp_unregister_congestion_control(type: &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 | |