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