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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
a7834745 TG |
2 | #ifndef __NET_SCHED_RED_H |
3 | #define __NET_SCHED_RED_H | |
4 | ||
a7834745 | 5 | #include <linux/types.h> |
187f1882 | 6 | #include <linux/bug.h> |
a7834745 TG |
7 | #include <net/pkt_sched.h> |
8 | #include <net/inet_ecn.h> | |
9 | #include <net/dsfield.h> | |
8af2a218 | 10 | #include <linux/reciprocal_div.h> |
a7834745 TG |
11 | |
12 | /* Random Early Detection (RED) algorithm. | |
13 | ======================================= | |
14 | ||
15 | Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways | |
16 | for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking. | |
17 | ||
18 | This file codes a "divisionless" version of RED algorithm | |
19 | as written down in Fig.17 of the paper. | |
20 | ||
21 | Short description. | |
22 | ------------------ | |
23 | ||
24 | When a new packet arrives we calculate the average queue length: | |
25 | ||
26 | avg = (1-W)*avg + W*current_queue_len, | |
27 | ||
28 | W is the filter time constant (chosen as 2^(-Wlog)), it controls | |
29 | the inertia of the algorithm. To allow larger bursts, W should be | |
30 | decreased. | |
31 | ||
32 | if (avg > th_max) -> packet marked (dropped). | |
33 | if (avg < th_min) -> packet passes. | |
34 | if (th_min < avg < th_max) we calculate probability: | |
35 | ||
36 | Pb = max_P * (avg - th_min)/(th_max-th_min) | |
37 | ||
38 | and mark (drop) packet with this probability. | |
39 | Pb changes from 0 (at avg==th_min) to max_P (avg==th_max). | |
40 | max_P should be small (not 1), usually 0.01..0.02 is good value. | |
41 | ||
42 | max_P is chosen as a number, so that max_P/(th_max-th_min) | |
43 | is a negative power of two in order arithmetics to contain | |
44 | only shifts. | |
45 | ||
46 | ||
47 | Parameters, settable by user: | |
48 | ----------------------------- | |
49 | ||
50 | qth_min - bytes (should be < qth_max/2) | |
51 | qth_max - bytes (should be at least 2*qth_min and less limit) | |
52 | Wlog - bits (<32) log(1/W). | |
53 | Plog - bits (<32) | |
54 | ||
55 | Plog is related to max_P by formula: | |
56 | ||
57 | max_P = (qth_max-qth_min)/2^Plog; | |
58 | ||
59 | F.e. if qth_max=128K and qth_min=32K, then Plog=22 | |
60 | corresponds to max_P=0.02 | |
61 | ||
62 | Scell_log | |
63 | Stab | |
64 | ||
65 | Lookup table for log((1-W)^(t/t_ave). | |
66 | ||
67 | ||
68 | NOTES: | |
69 | ||
70 | Upper bound on W. | |
71 | ----------------- | |
72 | ||
73 | If you want to allow bursts of L packets of size S, | |
74 | you should choose W: | |
75 | ||
76 | L + 1 - th_min/S < (1-(1-W)^L)/W | |
77 | ||
78 | th_min/S = 32 th_min/S = 4 | |
79 | ||
80 | log(W) L | |
81 | -1 33 | |
82 | -2 35 | |
83 | -3 39 | |
84 | -4 46 | |
85 | -5 57 | |
86 | -6 75 | |
87 | -7 101 | |
88 | -8 135 | |
89 | -9 190 | |
90 | etc. | |
91 | */ | |
92 | ||
8af2a218 ED |
93 | /* |
94 | * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM | |
95 | * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001 | |
96 | * | |
97 | * Every 500 ms: | |
98 | * if (avg > target and max_p <= 0.5) | |
99 | * increase max_p : max_p += alpha; | |
100 | * else if (avg < target and max_p >= 0.01) | |
101 | * decrease max_p : max_p *= beta; | |
102 | * | |
103 | * target :[qth_min + 0.4*(qth_min - qth_max), | |
104 | * qth_min + 0.6*(qth_min - qth_max)]. | |
105 | * alpha : min(0.01, max_p / 4) | |
106 | * beta : 0.9 | |
107 | * max_P is a Q0.32 fixed point number (with 32 bits mantissa) | |
108 | * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ] | |
109 | */ | |
110 | #define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100)) | |
111 | ||
112 | #define MAX_P_MIN (1 * RED_ONE_PERCENT) | |
113 | #define MAX_P_MAX (50 * RED_ONE_PERCENT) | |
114 | #define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4) | |
115 | ||
a7834745 TG |
116 | #define RED_STAB_SIZE 256 |
117 | #define RED_STAB_MASK (RED_STAB_SIZE - 1) | |
118 | ||
fd2c3ef7 | 119 | struct red_stats { |
a7834745 TG |
120 | u32 prob_drop; /* Early probability drops */ |
121 | u32 prob_mark; /* Early probability marks */ | |
122 | u32 forced_drop; /* Forced drops, qavg > max_thresh */ | |
123 | u32 forced_mark; /* Forced marks, qavg > max_thresh */ | |
124 | u32 pdrop; /* Drops due to queue limits */ | |
125 | u32 other; /* Drops due to drop() calls */ | |
a7834745 TG |
126 | }; |
127 | ||
fd2c3ef7 | 128 | struct red_parms { |
a7834745 | 129 | /* Parameters */ |
8af2a218 ED |
130 | u32 qth_min; /* Min avg length threshold: Wlog scaled */ |
131 | u32 qth_max; /* Max avg length threshold: Wlog scaled */ | |
a7834745 | 132 | u32 Scell_max; |
8af2a218 | 133 | u32 max_P; /* probability, [0 .. 1.0] 32 scaled */ |
809fa972 HFS |
134 | /* reciprocal_value(max_P / qth_delta) */ |
135 | struct reciprocal_value max_P_reciprocal; | |
8af2a218 ED |
136 | u32 qth_delta; /* max_th - min_th */ |
137 | u32 target_min; /* min_th + 0.4*(max_th - min_th) */ | |
138 | u32 target_max; /* min_th + 0.6*(max_th - min_th) */ | |
a7834745 TG |
139 | u8 Scell_log; |
140 | u8 Wlog; /* log(W) */ | |
141 | u8 Plog; /* random number bits */ | |
142 | u8 Stab[RED_STAB_SIZE]; | |
eeca6688 | 143 | }; |
a7834745 | 144 | |
eeca6688 | 145 | struct red_vars { |
a7834745 TG |
146 | /* Variables */ |
147 | int qcount; /* Number of packets since last random | |
148 | number generation */ | |
149 | u32 qR; /* Cached random number */ | |
150 | ||
8af2a218 | 151 | unsigned long qavg; /* Average queue length: Wlog scaled */ |
ea6a5d3b | 152 | ktime_t qidlestart; /* Start of current idle period */ |
a7834745 TG |
153 | }; |
154 | ||
8af2a218 | 155 | static inline u32 red_maxp(u8 Plog) |
a7834745 | 156 | { |
8af2a218 | 157 | return Plog < 32 ? (~0U >> Plog) : ~0U; |
a7834745 TG |
158 | } |
159 | ||
eeca6688 ED |
160 | static inline void red_set_vars(struct red_vars *v) |
161 | { | |
162 | /* Reset average queue length, the value is strictly bound | |
163 | * to the parameters below, reseting hurts a bit but leaving | |
164 | * it might result in an unreasonable qavg for a while. --TGR | |
165 | */ | |
166 | v->qavg = 0; | |
167 | ||
168 | v->qcount = -1; | |
169 | } | |
8af2a218 | 170 | |
8afa10cb NF |
171 | static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog) |
172 | { | |
173 | if (fls(qth_min) + Wlog > 32) | |
174 | return false; | |
175 | if (fls(qth_max) + Wlog > 32) | |
176 | return false; | |
177 | if (qth_max < qth_min) | |
178 | return false; | |
179 | return true; | |
180 | } | |
181 | ||
a7834745 TG |
182 | static inline void red_set_parms(struct red_parms *p, |
183 | u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog, | |
a73ed26b | 184 | u8 Scell_log, u8 *stab, u32 max_P) |
a7834745 | 185 | { |
8af2a218 | 186 | int delta = qth_max - qth_min; |
a73ed26b | 187 | u32 max_p_delta; |
8af2a218 | 188 | |
a7834745 TG |
189 | p->qth_min = qth_min << Wlog; |
190 | p->qth_max = qth_max << Wlog; | |
191 | p->Wlog = Wlog; | |
192 | p->Plog = Plog; | |
5c472203 | 193 | if (delta <= 0) |
8af2a218 ED |
194 | delta = 1; |
195 | p->qth_delta = delta; | |
a73ed26b ED |
196 | if (!max_P) { |
197 | max_P = red_maxp(Plog); | |
198 | max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ | |
199 | } | |
200 | p->max_P = max_P; | |
201 | max_p_delta = max_P / delta; | |
202 | max_p_delta = max(max_p_delta, 1U); | |
203 | p->max_P_reciprocal = reciprocal_value(max_p_delta); | |
8af2a218 ED |
204 | |
205 | /* RED Adaptative target : | |
206 | * [min_th + 0.4*(min_th - max_th), | |
207 | * min_th + 0.6*(min_th - max_th)]. | |
208 | */ | |
209 | delta /= 5; | |
210 | p->target_min = qth_min + 2*delta; | |
211 | p->target_max = qth_min + 3*delta; | |
212 | ||
a7834745 TG |
213 | p->Scell_log = Scell_log; |
214 | p->Scell_max = (255 << Scell_log); | |
215 | ||
ddecf0f4 ED |
216 | if (stab) |
217 | memcpy(p->Stab, stab, sizeof(p->Stab)); | |
a7834745 TG |
218 | } |
219 | ||
eeca6688 | 220 | static inline int red_is_idling(const struct red_vars *v) |
a7834745 | 221 | { |
2456e855 | 222 | return v->qidlestart != 0; |
a7834745 TG |
223 | } |
224 | ||
eeca6688 | 225 | static inline void red_start_of_idle_period(struct red_vars *v) |
a7834745 | 226 | { |
eeca6688 | 227 | v->qidlestart = ktime_get(); |
a7834745 TG |
228 | } |
229 | ||
eeca6688 | 230 | static inline void red_end_of_idle_period(struct red_vars *v) |
a7834745 | 231 | { |
2456e855 | 232 | v->qidlestart = 0; |
a7834745 TG |
233 | } |
234 | ||
eeca6688 | 235 | static inline void red_restart(struct red_vars *v) |
a7834745 | 236 | { |
eeca6688 ED |
237 | red_end_of_idle_period(v); |
238 | v->qavg = 0; | |
239 | v->qcount = -1; | |
a7834745 TG |
240 | } |
241 | ||
eeca6688 ED |
242 | static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p, |
243 | const struct red_vars *v) | |
a7834745 | 244 | { |
eeca6688 | 245 | s64 delta = ktime_us_delta(ktime_get(), v->qidlestart); |
ea6a5d3b | 246 | long us_idle = min_t(s64, delta, p->Scell_max); |
a7834745 TG |
247 | int shift; |
248 | ||
a7834745 TG |
249 | /* |
250 | * The problem: ideally, average length queue recalcultion should | |
251 | * be done over constant clock intervals. This is too expensive, so | |
252 | * that the calculation is driven by outgoing packets. | |
253 | * When the queue is idle we have to model this clock by hand. | |
254 | * | |
255 | * SF+VJ proposed to "generate": | |
256 | * | |
257 | * m = idletime / (average_pkt_size / bandwidth) | |
258 | * | |
259 | * dummy packets as a burst after idle time, i.e. | |
260 | * | |
4362aaf6 | 261 | * v->qavg *= (1-W)^m |
a7834745 TG |
262 | * |
263 | * This is an apparently overcomplicated solution (f.e. we have to | |
264 | * precompute a table to make this calculation in reasonable time) | |
265 | * I believe that a simpler model may be used here, | |
266 | * but it is field for experiments. | |
267 | */ | |
268 | ||
269 | shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK]; | |
270 | ||
271 | if (shift) | |
eeca6688 | 272 | return v->qavg >> shift; |
a7834745 TG |
273 | else { |
274 | /* Approximate initial part of exponent with linear function: | |
275 | * | |
276 | * (1-W)^m ~= 1-mW + ... | |
277 | * | |
278 | * Seems, it is the best solution to | |
279 | * problem of too coarse exponent tabulation. | |
280 | */ | |
eeca6688 | 281 | us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log; |
a7834745 | 282 | |
eeca6688 ED |
283 | if (us_idle < (v->qavg >> 1)) |
284 | return v->qavg - us_idle; | |
a7834745 | 285 | else |
eeca6688 | 286 | return v->qavg >> 1; |
a7834745 TG |
287 | } |
288 | } | |
289 | ||
8af2a218 | 290 | static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p, |
eeca6688 | 291 | const struct red_vars *v, |
a7834745 TG |
292 | unsigned int backlog) |
293 | { | |
294 | /* | |
4362aaf6 | 295 | * NOTE: v->qavg is fixed point number with point at Wlog. |
a7834745 TG |
296 | * The formula below is equvalent to floating point |
297 | * version: | |
298 | * | |
299 | * qavg = qavg*(1-W) + backlog*W; | |
300 | * | |
301 | * --ANK (980924) | |
302 | */ | |
eeca6688 | 303 | return v->qavg + (backlog - (v->qavg >> p->Wlog)); |
a7834745 TG |
304 | } |
305 | ||
8af2a218 | 306 | static inline unsigned long red_calc_qavg(const struct red_parms *p, |
eeca6688 | 307 | const struct red_vars *v, |
a7834745 TG |
308 | unsigned int backlog) |
309 | { | |
eeca6688 ED |
310 | if (!red_is_idling(v)) |
311 | return red_calc_qavg_no_idle_time(p, v, backlog); | |
a7834745 | 312 | else |
eeca6688 | 313 | return red_calc_qavg_from_idle_time(p, v); |
a7834745 TG |
314 | } |
315 | ||
8af2a218 ED |
316 | |
317 | static inline u32 red_random(const struct red_parms *p) | |
a7834745 | 318 | { |
63862b5b | 319 | return reciprocal_divide(prandom_u32(), p->max_P_reciprocal); |
a7834745 TG |
320 | } |
321 | ||
eeca6688 ED |
322 | static inline int red_mark_probability(const struct red_parms *p, |
323 | const struct red_vars *v, | |
324 | unsigned long qavg) | |
a7834745 TG |
325 | { |
326 | /* The formula used below causes questions. | |
327 | ||
8af2a218 ED |
328 | OK. qR is random number in the interval |
329 | (0..1/max_P)*(qth_max-qth_min) | |
a7834745 TG |
330 | i.e. 0..(2^Plog). If we used floating point |
331 | arithmetics, it would be: (2^Plog)*rnd_num, | |
332 | where rnd_num is less 1. | |
333 | ||
334 | Taking into account, that qavg have fixed | |
8af2a218 | 335 | point at Wlog, two lines |
a7834745 TG |
336 | below have the following floating point equivalent: |
337 | ||
338 | max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount | |
339 | ||
340 | Any questions? --ANK (980924) | |
341 | */ | |
eeca6688 | 342 | return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR); |
a7834745 TG |
343 | } |
344 | ||
345 | enum { | |
346 | RED_BELOW_MIN_THRESH, | |
347 | RED_BETWEEN_TRESH, | |
348 | RED_ABOVE_MAX_TRESH, | |
349 | }; | |
350 | ||
eeca6688 | 351 | static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg) |
a7834745 TG |
352 | { |
353 | if (qavg < p->qth_min) | |
354 | return RED_BELOW_MIN_THRESH; | |
355 | else if (qavg >= p->qth_max) | |
356 | return RED_ABOVE_MAX_TRESH; | |
357 | else | |
358 | return RED_BETWEEN_TRESH; | |
359 | } | |
360 | ||
361 | enum { | |
362 | RED_DONT_MARK, | |
363 | RED_PROB_MARK, | |
364 | RED_HARD_MARK, | |
365 | }; | |
366 | ||
eeca6688 ED |
367 | static inline int red_action(const struct red_parms *p, |
368 | struct red_vars *v, | |
369 | unsigned long qavg) | |
a7834745 TG |
370 | { |
371 | switch (red_cmp_thresh(p, qavg)) { | |
372 | case RED_BELOW_MIN_THRESH: | |
eeca6688 | 373 | v->qcount = -1; |
a7834745 TG |
374 | return RED_DONT_MARK; |
375 | ||
376 | case RED_BETWEEN_TRESH: | |
eeca6688 ED |
377 | if (++v->qcount) { |
378 | if (red_mark_probability(p, v, qavg)) { | |
379 | v->qcount = 0; | |
380 | v->qR = red_random(p); | |
a7834745 TG |
381 | return RED_PROB_MARK; |
382 | } | |
383 | } else | |
eeca6688 | 384 | v->qR = red_random(p); |
a7834745 TG |
385 | |
386 | return RED_DONT_MARK; | |
387 | ||
388 | case RED_ABOVE_MAX_TRESH: | |
eeca6688 | 389 | v->qcount = -1; |
a7834745 TG |
390 | return RED_HARD_MARK; |
391 | } | |
392 | ||
393 | BUG(); | |
394 | return RED_DONT_MARK; | |
395 | } | |
396 | ||
eeca6688 | 397 | static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v) |
8af2a218 ED |
398 | { |
399 | unsigned long qavg; | |
400 | u32 max_p_delta; | |
401 | ||
eeca6688 ED |
402 | qavg = v->qavg; |
403 | if (red_is_idling(v)) | |
404 | qavg = red_calc_qavg_from_idle_time(p, v); | |
8af2a218 | 405 | |
4362aaf6 | 406 | /* v->qavg is fixed point number with point at Wlog */ |
8af2a218 ED |
407 | qavg >>= p->Wlog; |
408 | ||
409 | if (qavg > p->target_max && p->max_P <= MAX_P_MAX) | |
410 | p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */ | |
411 | else if (qavg < p->target_min && p->max_P >= MAX_P_MIN) | |
412 | p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */ | |
413 | ||
414 | max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta); | |
a73ed26b | 415 | max_p_delta = max(max_p_delta, 1U); |
8af2a218 ED |
416 | p->max_P_reciprocal = reciprocal_value(max_p_delta); |
417 | } | |
a7834745 | 418 | #endif |