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 
118 struct 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 
127 struct 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 	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) */
137 	u8		Scell_log;
138 	u8		Wlog;		/* log(W)		*/
139 	u8		Plog;		/* random number bits	*/
140 	u8		Stab[RED_STAB_SIZE];
141 };
142 
143 struct red_vars {
144 	/* Variables */
145 	int		qcount;		/* Number of packets since last random
146 					   number generation */
147 	u32		qR;		/* Cached random number */
148 
149 	unsigned long	qavg;		/* Average queue length: Wlog scaled */
150 	ktime_t		qidlestart;	/* Start of current idle period */
151 };
152 
red_maxp(u8 Plog)153 static inline u32 red_maxp(u8 Plog)
154 {
155 	return Plog < 32 ? (~0U >> Plog) : ~0U;
156 }
157 
red_set_vars(struct red_vars * v)158 static 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 }
168 
red_set_parms(struct red_parms * p,u32 qth_min,u32 qth_max,u8 Wlog,u8 Plog,u8 Scell_log,u8 * stab,u32 max_P)169 static inline void red_set_parms(struct red_parms *p,
170 				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
171 				 u8 Scell_log, u8 *stab, u32 max_P)
172 {
173 	int delta = qth_max - qth_min;
174 	u32 max_p_delta;
175 
176 	p->qth_min	= qth_min << Wlog;
177 	p->qth_max	= qth_max << Wlog;
178 	p->Wlog		= Wlog;
179 	p->Plog		= Plog;
180 	if (delta < 0)
181 		delta = 1;
182 	p->qth_delta	= delta;
183 	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);
191 
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 
200 	p->Scell_log	= Scell_log;
201 	p->Scell_max	= (255 << Scell_log);
202 
203 	if (stab)
204 		memcpy(p->Stab, stab, sizeof(p->Stab));
205 }
206 
red_is_idling(const struct red_vars * v)207 static inline int red_is_idling(const struct red_vars *v)
208 {
209 	return v->qidlestart.tv64 != 0;
210 }
211 
red_start_of_idle_period(struct red_vars * v)212 static inline void red_start_of_idle_period(struct red_vars *v)
213 {
214 	v->qidlestart = ktime_get();
215 }
216 
red_end_of_idle_period(struct red_vars * v)217 static inline void red_end_of_idle_period(struct red_vars *v)
218 {
219 	v->qidlestart.tv64 = 0;
220 }
221 
red_restart(struct red_vars * v)222 static inline void red_restart(struct red_vars *v)
223 {
224 	red_end_of_idle_period(v);
225 	v->qavg = 0;
226 	v->qcount = -1;
227 }
228 
red_calc_qavg_from_idle_time(const struct red_parms * p,const struct red_vars * v)229 static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
230 							 const struct red_vars *v)
231 {
232 	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
233 	long us_idle = min_t(s64, delta, p->Scell_max);
234 	int  shift;
235 
236 	/*
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 	 *
248 	 * 	v->qavg *= (1-W)^m
249 	 *
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)
259 		return v->qavg >> shift;
260 	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 		 */
268 		us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
269 
270 		if (us_idle < (v->qavg >> 1))
271 			return v->qavg - us_idle;
272 		else
273 			return v->qavg >> 1;
274 	}
275 }
276 
red_calc_qavg_no_idle_time(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)277 static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
278 						       const struct red_vars *v,
279 						       unsigned int backlog)
280 {
281 	/*
282 	 * NOTE: v->qavg is fixed point number with point at Wlog.
283 	 * The formula below is equvalent to floating point
284 	 * version:
285 	 *
286 	 * 	qavg = qavg*(1-W) + backlog*W;
287 	 *
288 	 * --ANK (980924)
289 	 */
290 	return v->qavg + (backlog - (v->qavg >> p->Wlog));
291 }
292 
red_calc_qavg(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)293 static inline unsigned long red_calc_qavg(const struct red_parms *p,
294 					  const struct red_vars *v,
295 					  unsigned int backlog)
296 {
297 	if (!red_is_idling(v))
298 		return red_calc_qavg_no_idle_time(p, v, backlog);
299 	else
300 		return red_calc_qavg_from_idle_time(p, v);
301 }
302 
303 
red_random(const struct red_parms * p)304 static inline u32 red_random(const struct red_parms *p)
305 {
306 	return reciprocal_divide(net_random(), p->max_P_reciprocal);
307 }
308 
red_mark_probability(const struct red_parms * p,const struct red_vars * v,unsigned long qavg)309 static inline int red_mark_probability(const struct red_parms *p,
310 				       const struct red_vars *v,
311 				       unsigned long qavg)
312 {
313 	/* The formula used below causes questions.
314 
315 	   OK. qR is random number in the interval
316 		(0..1/max_P)*(qth_max-qth_min)
317 	   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
322 	   point at Wlog, two lines
323 	   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 	 */
329 	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
330 }
331 
332 enum {
333 	RED_BELOW_MIN_THRESH,
334 	RED_BETWEEN_TRESH,
335 	RED_ABOVE_MAX_TRESH,
336 };
337 
red_cmp_thresh(const struct red_parms * p,unsigned long qavg)338 static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
339 {
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 
348 enum {
349 	RED_DONT_MARK,
350 	RED_PROB_MARK,
351 	RED_HARD_MARK,
352 };
353 
red_action(const struct red_parms * p,struct red_vars * v,unsigned long qavg)354 static inline int red_action(const struct red_parms *p,
355 			     struct red_vars *v,
356 			     unsigned long qavg)
357 {
358 	switch (red_cmp_thresh(p, qavg)) {
359 		case RED_BELOW_MIN_THRESH:
360 			v->qcount = -1;
361 			return RED_DONT_MARK;
362 
363 		case RED_BETWEEN_TRESH:
364 			if (++v->qcount) {
365 				if (red_mark_probability(p, v, qavg)) {
366 					v->qcount = 0;
367 					v->qR = red_random(p);
368 					return RED_PROB_MARK;
369 				}
370 			} else
371 				v->qR = red_random(p);
372 
373 			return RED_DONT_MARK;
374 
375 		case RED_ABOVE_MAX_TRESH:
376 			v->qcount = -1;
377 			return RED_HARD_MARK;
378 	}
379 
380 	BUG();
381 	return RED_DONT_MARK;
382 }
383 
red_adaptative_algo(struct red_parms * p,struct red_vars * v)384 static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
385 {
386 	unsigned long qavg;
387 	u32 max_p_delta;
388 
389 	qavg = v->qavg;
390 	if (red_is_idling(v))
391 		qavg = red_calc_qavg_from_idle_time(p, v);
392 
393 	/* v->qavg is fixed point number with point at Wlog */
394 	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);
402 	max_p_delta = max(max_p_delta, 1U);
403 	p->max_P_reciprocal = reciprocal_value(max_p_delta);
404 }
405 #endif
406