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Thomas Grafa7834742005-11-05 21:14:03 +01001#ifndef __NET_SCHED_RED_H
2#define __NET_SCHED_RED_H
3
Thomas Grafa7834742005-11-05 21:14:03 +01004#include <linux/types.h>
Paul Gortmaker187f1882011-11-23 20:12:59 -05005#include <linux/bug.h>
Thomas Grafa7834742005-11-05 21:14:03 +01006#include <net/pkt_sched.h>
7#include <net/inet_ecn.h>
8#include <net/dsfield.h>
Eric Dumazet8af2a212011-12-08 06:06:03 +00009#include <linux/reciprocal_div.h>
Thomas Grafa7834742005-11-05 21:14:03 +010010
11/* Random Early Detection (RED) algorithm.
12 =======================================
13
14 Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
15 for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
16
17 This file codes a "divisionless" version of RED algorithm
18 as written down in Fig.17 of the paper.
19
20 Short description.
21 ------------------
22
23 When a new packet arrives we calculate the average queue length:
24
25 avg = (1-W)*avg + W*current_queue_len,
26
27 W is the filter time constant (chosen as 2^(-Wlog)), it controls
28 the inertia of the algorithm. To allow larger bursts, W should be
29 decreased.
30
31 if (avg > th_max) -> packet marked (dropped).
32 if (avg < th_min) -> packet passes.
33 if (th_min < avg < th_max) we calculate probability:
34
35 Pb = max_P * (avg - th_min)/(th_max-th_min)
36
37 and mark (drop) packet with this probability.
38 Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
39 max_P should be small (not 1), usually 0.01..0.02 is good value.
40
41 max_P is chosen as a number, so that max_P/(th_max-th_min)
42 is a negative power of two in order arithmetics to contain
43 only shifts.
44
45
46 Parameters, settable by user:
47 -----------------------------
48
49 qth_min - bytes (should be < qth_max/2)
50 qth_max - bytes (should be at least 2*qth_min and less limit)
51 Wlog - bits (<32) log(1/W).
52 Plog - bits (<32)
53
54 Plog is related to max_P by formula:
55
56 max_P = (qth_max-qth_min)/2^Plog;
57
58 F.e. if qth_max=128K and qth_min=32K, then Plog=22
59 corresponds to max_P=0.02
60
61 Scell_log
62 Stab
63
64 Lookup table for log((1-W)^(t/t_ave).
65
66
67 NOTES:
68
69 Upper bound on W.
70 -----------------
71
72 If you want to allow bursts of L packets of size S,
73 you should choose W:
74
75 L + 1 - th_min/S < (1-(1-W)^L)/W
76
77 th_min/S = 32 th_min/S = 4
78
79 log(W) L
80 -1 33
81 -2 35
82 -3 39
83 -4 46
84 -5 57
85 -6 75
86 -7 101
87 -8 135
88 -9 190
89 etc.
90 */
91
Eric Dumazet8af2a212011-12-08 06:06:03 +000092/*
93 * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
94 * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
95 *
96 * Every 500 ms:
97 * if (avg > target and max_p <= 0.5)
98 * increase max_p : max_p += alpha;
99 * else if (avg < target and max_p >= 0.01)
100 * decrease max_p : max_p *= beta;
101 *
102 * target :[qth_min + 0.4*(qth_min - qth_max),
103 * qth_min + 0.6*(qth_min - qth_max)].
104 * alpha : min(0.01, max_p / 4)
105 * beta : 0.9
106 * max_P is a Q0.32 fixed point number (with 32 bits mantissa)
107 * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
108 */
109#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))
110
111#define MAX_P_MIN (1 * RED_ONE_PERCENT)
112#define MAX_P_MAX (50 * RED_ONE_PERCENT)
113#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)
114
Thomas Grafa7834742005-11-05 21:14:03 +0100115#define RED_STAB_SIZE 256
116#define RED_STAB_MASK (RED_STAB_SIZE - 1)
117
Eric Dumazetfd2c3ef2009-11-03 03:26:03 +0000118struct red_stats {
Thomas Grafa7834742005-11-05 21:14:03 +0100119 u32 prob_drop; /* Early probability drops */
120 u32 prob_mark; /* Early probability marks */
121 u32 forced_drop; /* Forced drops, qavg > max_thresh */
122 u32 forced_mark; /* Forced marks, qavg > max_thresh */
123 u32 pdrop; /* Drops due to queue limits */
124 u32 other; /* Drops due to drop() calls */
Thomas Grafa7834742005-11-05 21:14:03 +0100125};
126
Eric Dumazetfd2c3ef2009-11-03 03:26:03 +0000127struct red_parms {
Thomas Grafa7834742005-11-05 21:14:03 +0100128 /* Parameters */
Eric Dumazet8af2a212011-12-08 06:06:03 +0000129 u32 qth_min; /* Min avg length threshold: Wlog scaled */
130 u32 qth_max; /* Max avg length threshold: Wlog scaled */
Thomas Grafa7834742005-11-05 21:14:03 +0100131 u32 Scell_max;
Eric Dumazet8af2a212011-12-08 06:06:03 +0000132 u32 max_P; /* probability, [0 .. 1.0] 32 scaled */
133 u32 max_P_reciprocal; /* reciprocal_value(max_P / qth_delta) */
134 u32 qth_delta; /* max_th - min_th */
135 u32 target_min; /* min_th + 0.4*(max_th - min_th) */
136 u32 target_max; /* min_th + 0.6*(max_th - min_th) */
Thomas Grafa7834742005-11-05 21:14:03 +0100137 u8 Scell_log;
138 u8 Wlog; /* log(W) */
139 u8 Plog; /* random number bits */
140 u8 Stab[RED_STAB_SIZE];
Eric Dumazeteeca6682012-01-05 02:25:16 +0000141};
Thomas Grafa7834742005-11-05 21:14:03 +0100142
Eric Dumazeteeca6682012-01-05 02:25:16 +0000143struct red_vars {
Thomas Grafa7834742005-11-05 21:14:03 +0100144 /* Variables */
145 int qcount; /* Number of packets since last random
146 number generation */
147 u32 qR; /* Cached random number */
148
Eric Dumazet8af2a212011-12-08 06:06:03 +0000149 unsigned long qavg; /* Average queue length: Wlog scaled */
Eric Dumazetea6a5d32011-11-30 12:10:53 +0000150 ktime_t qidlestart; /* Start of current idle period */
Thomas Grafa7834742005-11-05 21:14:03 +0100151};
152
Eric Dumazet8af2a212011-12-08 06:06:03 +0000153static inline u32 red_maxp(u8 Plog)
Thomas Grafa7834742005-11-05 21:14:03 +0100154{
Eric Dumazet8af2a212011-12-08 06:06:03 +0000155 return Plog < 32 ? (~0U >> Plog) : ~0U;
Thomas Grafa7834742005-11-05 21:14:03 +0100156}
157
Eric Dumazeteeca6682012-01-05 02:25:16 +0000158static inline void red_set_vars(struct red_vars *v)
159{
160 /* Reset average queue length, the value is strictly bound
161 * to the parameters below, reseting hurts a bit but leaving
162 * it might result in an unreasonable qavg for a while. --TGR
163 */
164 v->qavg = 0;
165
166 v->qcount = -1;
167}
Eric Dumazet8af2a212011-12-08 06:06:03 +0000168
Thomas Grafa7834742005-11-05 21:14:03 +0100169static inline void red_set_parms(struct red_parms *p,
170 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
Eric Dumazeta73ed262011-12-09 02:46:45 +0000171 u8 Scell_log, u8 *stab, u32 max_P)
Thomas Grafa7834742005-11-05 21:14:03 +0100172{
Eric Dumazet8af2a212011-12-08 06:06:03 +0000173 int delta = qth_max - qth_min;
Eric Dumazeta73ed262011-12-09 02:46:45 +0000174 u32 max_p_delta;
Eric Dumazet8af2a212011-12-08 06:06:03 +0000175
Thomas Grafa7834742005-11-05 21:14:03 +0100176 p->qth_min = qth_min << Wlog;
177 p->qth_max = qth_max << Wlog;
178 p->Wlog = Wlog;
179 p->Plog = Plog;
Eric Dumazet8af2a212011-12-08 06:06:03 +0000180 if (delta < 0)
181 delta = 1;
182 p->qth_delta = delta;
Eric Dumazeta73ed262011-12-09 02:46:45 +0000183 if (!max_P) {
184 max_P = red_maxp(Plog);
185 max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */
186 }
187 p->max_P = max_P;
188 max_p_delta = max_P / delta;
189 max_p_delta = max(max_p_delta, 1U);
190 p->max_P_reciprocal = reciprocal_value(max_p_delta);
Eric Dumazet8af2a212011-12-08 06:06:03 +0000191
192 /* RED Adaptative target :
193 * [min_th + 0.4*(min_th - max_th),
194 * min_th + 0.6*(min_th - max_th)].
195 */
196 delta /= 5;
197 p->target_min = qth_min + 2*delta;
198 p->target_max = qth_min + 3*delta;
199
Thomas Grafa7834742005-11-05 21:14:03 +0100200 p->Scell_log = Scell_log;
201 p->Scell_max = (255 << Scell_log);
202
Eric Dumazetddecf0f2012-01-06 06:31:44 +0000203 if (stab)
204 memcpy(p->Stab, stab, sizeof(p->Stab));
Thomas Grafa7834742005-11-05 21:14:03 +0100205}
206
Eric Dumazeteeca6682012-01-05 02:25:16 +0000207static inline int red_is_idling(const struct red_vars *v)
Thomas Grafa7834742005-11-05 21:14:03 +0100208{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000209 return v->qidlestart.tv64 != 0;
Thomas Grafa7834742005-11-05 21:14:03 +0100210}
211
Eric Dumazeteeca6682012-01-05 02:25:16 +0000212static inline void red_start_of_idle_period(struct red_vars *v)
Thomas Grafa7834742005-11-05 21:14:03 +0100213{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000214 v->qidlestart = ktime_get();
Thomas Grafa7834742005-11-05 21:14:03 +0100215}
216
Eric Dumazeteeca6682012-01-05 02:25:16 +0000217static inline void red_end_of_idle_period(struct red_vars *v)
Thomas Grafa7834742005-11-05 21:14:03 +0100218{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000219 v->qidlestart.tv64 = 0;
Thomas Grafa7834742005-11-05 21:14:03 +0100220}
221
Eric Dumazeteeca6682012-01-05 02:25:16 +0000222static inline void red_restart(struct red_vars *v)
Thomas Grafa7834742005-11-05 21:14:03 +0100223{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000224 red_end_of_idle_period(v);
225 v->qavg = 0;
226 v->qcount = -1;
Thomas Grafa7834742005-11-05 21:14:03 +0100227}
228
Eric Dumazeteeca6682012-01-05 02:25:16 +0000229static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
230 const struct red_vars *v)
Thomas Grafa7834742005-11-05 21:14:03 +0100231{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000232 s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
Eric Dumazetea6a5d32011-11-30 12:10:53 +0000233 long us_idle = min_t(s64, delta, p->Scell_max);
Thomas Grafa7834742005-11-05 21:14:03 +0100234 int shift;
235
Thomas Grafa7834742005-11-05 21:14:03 +0100236 /*
237 * The problem: ideally, average length queue recalcultion should
238 * be done over constant clock intervals. This is too expensive, so
239 * that the calculation is driven by outgoing packets.
240 * When the queue is idle we have to model this clock by hand.
241 *
242 * SF+VJ proposed to "generate":
243 *
244 * m = idletime / (average_pkt_size / bandwidth)
245 *
246 * dummy packets as a burst after idle time, i.e.
247 *
David Ward4362aaf2012-04-16 03:17:22 +0000248 * v->qavg *= (1-W)^m
Thomas Grafa7834742005-11-05 21:14:03 +0100249 *
250 * This is an apparently overcomplicated solution (f.e. we have to
251 * precompute a table to make this calculation in reasonable time)
252 * I believe that a simpler model may be used here,
253 * but it is field for experiments.
254 */
255
256 shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
257
258 if (shift)
Eric Dumazeteeca6682012-01-05 02:25:16 +0000259 return v->qavg >> shift;
Thomas Grafa7834742005-11-05 21:14:03 +0100260 else {
261 /* Approximate initial part of exponent with linear function:
262 *
263 * (1-W)^m ~= 1-mW + ...
264 *
265 * Seems, it is the best solution to
266 * problem of too coarse exponent tabulation.
267 */
Eric Dumazeteeca6682012-01-05 02:25:16 +0000268 us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
Thomas Grafa7834742005-11-05 21:14:03 +0100269
Eric Dumazeteeca6682012-01-05 02:25:16 +0000270 if (us_idle < (v->qavg >> 1))
271 return v->qavg - us_idle;
Thomas Grafa7834742005-11-05 21:14:03 +0100272 else
Eric Dumazeteeca6682012-01-05 02:25:16 +0000273 return v->qavg >> 1;
Thomas Grafa7834742005-11-05 21:14:03 +0100274 }
275}
276
Eric Dumazet8af2a212011-12-08 06:06:03 +0000277static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
Eric Dumazeteeca6682012-01-05 02:25:16 +0000278 const struct red_vars *v,
Thomas Grafa7834742005-11-05 21:14:03 +0100279 unsigned int backlog)
280{
281 /*
David Ward4362aaf2012-04-16 03:17:22 +0000282 * NOTE: v->qavg is fixed point number with point at Wlog.
Thomas Grafa7834742005-11-05 21:14:03 +0100283 * The formula below is equvalent to floating point
284 * version:
285 *
286 * qavg = qavg*(1-W) + backlog*W;
287 *
288 * --ANK (980924)
289 */
Eric Dumazeteeca6682012-01-05 02:25:16 +0000290 return v->qavg + (backlog - (v->qavg >> p->Wlog));
Thomas Grafa7834742005-11-05 21:14:03 +0100291}
292
Eric Dumazet8af2a212011-12-08 06:06:03 +0000293static inline unsigned long red_calc_qavg(const struct red_parms *p,
Eric Dumazeteeca6682012-01-05 02:25:16 +0000294 const struct red_vars *v,
Thomas Grafa7834742005-11-05 21:14:03 +0100295 unsigned int backlog)
296{
Eric Dumazeteeca6682012-01-05 02:25:16 +0000297 if (!red_is_idling(v))
298 return red_calc_qavg_no_idle_time(p, v, backlog);
Thomas Grafa7834742005-11-05 21:14:03 +0100299 else
Eric Dumazeteeca6682012-01-05 02:25:16 +0000300 return red_calc_qavg_from_idle_time(p, v);
Thomas Grafa7834742005-11-05 21:14:03 +0100301}
302
Eric Dumazet8af2a212011-12-08 06:06:03 +0000303
304static inline u32 red_random(const struct red_parms *p)
Thomas Grafa7834742005-11-05 21:14:03 +0100305{
Eric Dumazet8af2a212011-12-08 06:06:03 +0000306 return reciprocal_divide(net_random(), p->max_P_reciprocal);
Thomas Grafa7834742005-11-05 21:14:03 +0100307}
308
Eric Dumazeteeca6682012-01-05 02:25:16 +0000309static inline int red_mark_probability(const struct red_parms *p,
310 const struct red_vars *v,
311 unsigned long qavg)
Thomas Grafa7834742005-11-05 21:14:03 +0100312{
313 /* The formula used below causes questions.
314
Eric Dumazet8af2a212011-12-08 06:06:03 +0000315 OK. qR is random number in the interval
316 (0..1/max_P)*(qth_max-qth_min)
Thomas Grafa7834742005-11-05 21:14:03 +0100317 i.e. 0..(2^Plog). If we used floating point
318 arithmetics, it would be: (2^Plog)*rnd_num,
319 where rnd_num is less 1.
320
321 Taking into account, that qavg have fixed
Eric Dumazet8af2a212011-12-08 06:06:03 +0000322 point at Wlog, two lines
Thomas Grafa7834742005-11-05 21:14:03 +0100323 below have the following floating point equivalent:
324
325 max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
326
327 Any questions? --ANK (980924)
328 */
Eric Dumazeteeca6682012-01-05 02:25:16 +0000329 return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
Thomas Grafa7834742005-11-05 21:14:03 +0100330}
331
332enum {
333 RED_BELOW_MIN_THRESH,
334 RED_BETWEEN_TRESH,
335 RED_ABOVE_MAX_TRESH,
336};
337
Eric Dumazeteeca6682012-01-05 02:25:16 +0000338static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
Thomas Grafa7834742005-11-05 21:14:03 +0100339{
340 if (qavg < p->qth_min)
341 return RED_BELOW_MIN_THRESH;
342 else if (qavg >= p->qth_max)
343 return RED_ABOVE_MAX_TRESH;
344 else
345 return RED_BETWEEN_TRESH;
346}
347
348enum {
349 RED_DONT_MARK,
350 RED_PROB_MARK,
351 RED_HARD_MARK,
352};
353
Eric Dumazeteeca6682012-01-05 02:25:16 +0000354static inline int red_action(const struct red_parms *p,
355 struct red_vars *v,
356 unsigned long qavg)
Thomas Grafa7834742005-11-05 21:14:03 +0100357{
358 switch (red_cmp_thresh(p, qavg)) {
359 case RED_BELOW_MIN_THRESH:
Eric Dumazeteeca6682012-01-05 02:25:16 +0000360 v->qcount = -1;
Thomas Grafa7834742005-11-05 21:14:03 +0100361 return RED_DONT_MARK;
362
363 case RED_BETWEEN_TRESH:
Eric Dumazeteeca6682012-01-05 02:25:16 +0000364 if (++v->qcount) {
365 if (red_mark_probability(p, v, qavg)) {
366 v->qcount = 0;
367 v->qR = red_random(p);
Thomas Grafa7834742005-11-05 21:14:03 +0100368 return RED_PROB_MARK;
369 }
370 } else
Eric Dumazeteeca6682012-01-05 02:25:16 +0000371 v->qR = red_random(p);
Thomas Grafa7834742005-11-05 21:14:03 +0100372
373 return RED_DONT_MARK;
374
375 case RED_ABOVE_MAX_TRESH:
Eric Dumazeteeca6682012-01-05 02:25:16 +0000376 v->qcount = -1;
Thomas Grafa7834742005-11-05 21:14:03 +0100377 return RED_HARD_MARK;
378 }
379
380 BUG();
381 return RED_DONT_MARK;
382}
383
Eric Dumazeteeca6682012-01-05 02:25:16 +0000384static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
Eric Dumazet8af2a212011-12-08 06:06:03 +0000385{
386 unsigned long qavg;
387 u32 max_p_delta;
388
Eric Dumazeteeca6682012-01-05 02:25:16 +0000389 qavg = v->qavg;
390 if (red_is_idling(v))
391 qavg = red_calc_qavg_from_idle_time(p, v);
Eric Dumazet8af2a212011-12-08 06:06:03 +0000392
David Ward4362aaf2012-04-16 03:17:22 +0000393 /* v->qavg is fixed point number with point at Wlog */
Eric Dumazet8af2a212011-12-08 06:06:03 +0000394 qavg >>= p->Wlog;
395
396 if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
397 p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
398 else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
399 p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */
400
401 max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
Eric Dumazeta73ed262011-12-09 02:46:45 +0000402 max_p_delta = max(max_p_delta, 1U);
Eric Dumazet8af2a212011-12-08 06:06:03 +0000403 p->max_P_reciprocal = reciprocal_value(max_p_delta);
404}
Thomas Grafa7834742005-11-05 21:14:03 +0100405#endif