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