1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __NET_SCHED_RED_H
3 #define __NET_SCHED_RED_H
4 
5 #include <linux/types.h>
6 #include <linux/bug.h>
7 #include <net/pkt_sched.h>
8 #include <net/inet_ecn.h>
9 #include <net/dsfield.h>
10 #include <linux/reciprocal_div.h>
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 
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 
116 #define RED_STAB_SIZE	256
117 #define RED_STAB_MASK	(RED_STAB_SIZE - 1)
118 
119 struct red_stats {
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 */
126 };
127 
128 struct red_parms {
129 	/* Parameters */
130 	u32		qth_min;	/* Min avg length threshold: Wlog scaled */
131 	u32		qth_max;	/* Max avg length threshold: Wlog scaled */
132 	u32		Scell_max;
133 	u32		max_P;		/* probability, [0 .. 1.0] 32 scaled */
134 	/* reciprocal_value(max_P / qth_delta) */
135 	struct reciprocal_value	max_P_reciprocal;
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) */
139 	u8		Scell_log;
140 	u8		Wlog;		/* log(W)		*/
141 	u8		Plog;		/* random number bits	*/
142 	u8		Stab[RED_STAB_SIZE];
143 };
144 
145 struct red_vars {
146 	/* Variables */
147 	int		qcount;		/* Number of packets since last random
148 					   number generation */
149 	u32		qR;		/* Cached random number */
150 
151 	unsigned long	qavg;		/* Average queue length: Wlog scaled */
152 	ktime_t		qidlestart;	/* Start of current idle period */
153 };
154 
red_maxp(u8 Plog)155 static inline u32 red_maxp(u8 Plog)
156 {
157 	return Plog < 32 ? (~0U >> Plog) : ~0U;
158 }
159 
red_set_vars(struct red_vars * v)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 }
170 
red_check_params(u32 qth_min,u32 qth_max,u8 Wlog,u8 Scell_log,u8 * stab)171 static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog,
172 				    u8 Scell_log, u8 *stab)
173 {
174 	if (fls(qth_min) + Wlog >= 32)
175 		return false;
176 	if (fls(qth_max) + Wlog >= 32)
177 		return false;
178 	if (Scell_log >= 32)
179 		return false;
180 	if (qth_max < qth_min)
181 		return false;
182 	if (stab) {
183 		int i;
184 
185 		for (i = 0; i < RED_STAB_SIZE; i++)
186 			if (stab[i] >= 32)
187 				return false;
188 	}
189 	return true;
190 }
191 
red_get_flags(unsigned char qopt_flags,unsigned char historic_mask,struct nlattr * flags_attr,unsigned char supported_mask,struct nla_bitfield32 * p_flags,unsigned char * p_userbits,struct netlink_ext_ack * extack)192 static inline int red_get_flags(unsigned char qopt_flags,
193 				unsigned char historic_mask,
194 				struct nlattr *flags_attr,
195 				unsigned char supported_mask,
196 				struct nla_bitfield32 *p_flags,
197 				unsigned char *p_userbits,
198 				struct netlink_ext_ack *extack)
199 {
200 	struct nla_bitfield32 flags;
201 
202 	if (qopt_flags && flags_attr) {
203 		NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute");
204 		return -EINVAL;
205 	}
206 
207 	if (flags_attr) {
208 		flags = nla_get_bitfield32(flags_attr);
209 	} else {
210 		flags.selector = historic_mask;
211 		flags.value = qopt_flags & historic_mask;
212 	}
213 
214 	*p_flags = flags;
215 	*p_userbits = qopt_flags & ~historic_mask;
216 	return 0;
217 }
218 
red_validate_flags(unsigned char flags,struct netlink_ext_ack * extack)219 static inline int red_validate_flags(unsigned char flags,
220 				     struct netlink_ext_ack *extack)
221 {
222 	if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) {
223 		NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN");
224 		return -EINVAL;
225 	}
226 
227 	return 0;
228 }
229 
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)230 static inline void red_set_parms(struct red_parms *p,
231 				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
232 				 u8 Scell_log, u8 *stab, u32 max_P)
233 {
234 	int delta = qth_max - qth_min;
235 	u32 max_p_delta;
236 
237 	p->qth_min	= qth_min << Wlog;
238 	p->qth_max	= qth_max << Wlog;
239 	p->Wlog		= Wlog;
240 	p->Plog		= Plog;
241 	if (delta <= 0)
242 		delta = 1;
243 	p->qth_delta	= delta;
244 	if (!max_P) {
245 		max_P = red_maxp(Plog);
246 		max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */
247 	}
248 	p->max_P = max_P;
249 	max_p_delta = max_P / delta;
250 	max_p_delta = max(max_p_delta, 1U);
251 	p->max_P_reciprocal  = reciprocal_value(max_p_delta);
252 
253 	/* RED Adaptative target :
254 	 * [min_th + 0.4*(min_th - max_th),
255 	 *  min_th + 0.6*(min_th - max_th)].
256 	 */
257 	delta /= 5;
258 	p->target_min = qth_min + 2*delta;
259 	p->target_max = qth_min + 3*delta;
260 
261 	p->Scell_log	= Scell_log;
262 	p->Scell_max	= (255 << Scell_log);
263 
264 	if (stab)
265 		memcpy(p->Stab, stab, sizeof(p->Stab));
266 }
267 
red_is_idling(const struct red_vars * v)268 static inline int red_is_idling(const struct red_vars *v)
269 {
270 	return v->qidlestart != 0;
271 }
272 
red_start_of_idle_period(struct red_vars * v)273 static inline void red_start_of_idle_period(struct red_vars *v)
274 {
275 	v->qidlestart = ktime_get();
276 }
277 
red_end_of_idle_period(struct red_vars * v)278 static inline void red_end_of_idle_period(struct red_vars *v)
279 {
280 	v->qidlestart = 0;
281 }
282 
red_restart(struct red_vars * v)283 static inline void red_restart(struct red_vars *v)
284 {
285 	red_end_of_idle_period(v);
286 	v->qavg = 0;
287 	v->qcount = -1;
288 }
289 
red_calc_qavg_from_idle_time(const struct red_parms * p,const struct red_vars * v)290 static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
291 							 const struct red_vars *v)
292 {
293 	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
294 	long us_idle = min_t(s64, delta, p->Scell_max);
295 	int  shift;
296 
297 	/*
298 	 * The problem: ideally, average length queue recalculation should
299 	 * be done over constant clock intervals. This is too expensive, so
300 	 * that the calculation is driven by outgoing packets.
301 	 * When the queue is idle we have to model this clock by hand.
302 	 *
303 	 * SF+VJ proposed to "generate":
304 	 *
305 	 *	m = idletime / (average_pkt_size / bandwidth)
306 	 *
307 	 * dummy packets as a burst after idle time, i.e.
308 	 *
309 	 * 	v->qavg *= (1-W)^m
310 	 *
311 	 * This is an apparently overcomplicated solution (f.e. we have to
312 	 * precompute a table to make this calculation in reasonable time)
313 	 * I believe that a simpler model may be used here,
314 	 * but it is field for experiments.
315 	 */
316 
317 	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
318 
319 	if (shift)
320 		return v->qavg >> shift;
321 	else {
322 		/* Approximate initial part of exponent with linear function:
323 		 *
324 		 * 	(1-W)^m ~= 1-mW + ...
325 		 *
326 		 * Seems, it is the best solution to
327 		 * problem of too coarse exponent tabulation.
328 		 */
329 		us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
330 
331 		if (us_idle < (v->qavg >> 1))
332 			return v->qavg - us_idle;
333 		else
334 			return v->qavg >> 1;
335 	}
336 }
337 
red_calc_qavg_no_idle_time(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)338 static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
339 						       const struct red_vars *v,
340 						       unsigned int backlog)
341 {
342 	/*
343 	 * NOTE: v->qavg is fixed point number with point at Wlog.
344 	 * The formula below is equvalent to floating point
345 	 * version:
346 	 *
347 	 * 	qavg = qavg*(1-W) + backlog*W;
348 	 *
349 	 * --ANK (980924)
350 	 */
351 	return v->qavg + (backlog - (v->qavg >> p->Wlog));
352 }
353 
red_calc_qavg(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)354 static inline unsigned long red_calc_qavg(const struct red_parms *p,
355 					  const struct red_vars *v,
356 					  unsigned int backlog)
357 {
358 	if (!red_is_idling(v))
359 		return red_calc_qavg_no_idle_time(p, v, backlog);
360 	else
361 		return red_calc_qavg_from_idle_time(p, v);
362 }
363 
364 
red_random(const struct red_parms * p)365 static inline u32 red_random(const struct red_parms *p)
366 {
367 	return reciprocal_divide(prandom_u32(), p->max_P_reciprocal);
368 }
369 
red_mark_probability(const struct red_parms * p,const struct red_vars * v,unsigned long qavg)370 static inline int red_mark_probability(const struct red_parms *p,
371 				       const struct red_vars *v,
372 				       unsigned long qavg)
373 {
374 	/* The formula used below causes questions.
375 
376 	   OK. qR is random number in the interval
377 		(0..1/max_P)*(qth_max-qth_min)
378 	   i.e. 0..(2^Plog). If we used floating point
379 	   arithmetics, it would be: (2^Plog)*rnd_num,
380 	   where rnd_num is less 1.
381 
382 	   Taking into account, that qavg have fixed
383 	   point at Wlog, two lines
384 	   below have the following floating point equivalent:
385 
386 	   max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
387 
388 	   Any questions? --ANK (980924)
389 	 */
390 	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
391 }
392 
393 enum {
394 	RED_BELOW_MIN_THRESH,
395 	RED_BETWEEN_TRESH,
396 	RED_ABOVE_MAX_TRESH,
397 };
398 
red_cmp_thresh(const struct red_parms * p,unsigned long qavg)399 static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
400 {
401 	if (qavg < p->qth_min)
402 		return RED_BELOW_MIN_THRESH;
403 	else if (qavg >= p->qth_max)
404 		return RED_ABOVE_MAX_TRESH;
405 	else
406 		return RED_BETWEEN_TRESH;
407 }
408 
409 enum {
410 	RED_DONT_MARK,
411 	RED_PROB_MARK,
412 	RED_HARD_MARK,
413 };
414 
red_action(const struct red_parms * p,struct red_vars * v,unsigned long qavg)415 static inline int red_action(const struct red_parms *p,
416 			     struct red_vars *v,
417 			     unsigned long qavg)
418 {
419 	switch (red_cmp_thresh(p, qavg)) {
420 		case RED_BELOW_MIN_THRESH:
421 			v->qcount = -1;
422 			return RED_DONT_MARK;
423 
424 		case RED_BETWEEN_TRESH:
425 			if (++v->qcount) {
426 				if (red_mark_probability(p, v, qavg)) {
427 					v->qcount = 0;
428 					v->qR = red_random(p);
429 					return RED_PROB_MARK;
430 				}
431 			} else
432 				v->qR = red_random(p);
433 
434 			return RED_DONT_MARK;
435 
436 		case RED_ABOVE_MAX_TRESH:
437 			v->qcount = -1;
438 			return RED_HARD_MARK;
439 	}
440 
441 	BUG();
442 	return RED_DONT_MARK;
443 }
444 
red_adaptative_algo(struct red_parms * p,struct red_vars * v)445 static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
446 {
447 	unsigned long qavg;
448 	u32 max_p_delta;
449 
450 	qavg = v->qavg;
451 	if (red_is_idling(v))
452 		qavg = red_calc_qavg_from_idle_time(p, v);
453 
454 	/* v->qavg is fixed point number with point at Wlog */
455 	qavg >>= p->Wlog;
456 
457 	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
458 		p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
459 	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
460 		p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */
461 
462 	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
463 	max_p_delta = max(max_p_delta, 1U);
464 	p->max_P_reciprocal = reciprocal_value(max_p_delta);
465 }
466 #endif
467