xref: /openbmc/linux/include/net/red.h (revision a251c17a)
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 };
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 	/* 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 
144 struct 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 
red_maxp(u8 Plog)154 static inline u32 red_maxp(u8 Plog)
155 {
156 	return Plog < 32 ? (~0U >> Plog) : ~0U;
157 }
158 
red_set_vars(struct red_vars * v)159 static 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 
red_check_params(u32 qth_min,u32 qth_max,u8 Wlog,u8 Scell_log,u8 * stab)170 static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog,
171 				    u8 Scell_log, u8 *stab)
172 {
173 	if (fls(qth_min) + Wlog >= 32)
174 		return false;
175 	if (fls(qth_max) + Wlog >= 32)
176 		return false;
177 	if (Scell_log >= 32)
178 		return false;
179 	if (qth_max < qth_min)
180 		return false;
181 	if (stab) {
182 		int i;
183 
184 		for (i = 0; i < RED_STAB_SIZE; i++)
185 			if (stab[i] >= 32)
186 				return false;
187 	}
188 	return true;
189 }
190 
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)191 static inline int red_get_flags(unsigned char qopt_flags,
192 				unsigned char historic_mask,
193 				struct nlattr *flags_attr,
194 				unsigned char supported_mask,
195 				struct nla_bitfield32 *p_flags,
196 				unsigned char *p_userbits,
197 				struct netlink_ext_ack *extack)
198 {
199 	struct nla_bitfield32 flags;
200 
201 	if (qopt_flags && flags_attr) {
202 		NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute");
203 		return -EINVAL;
204 	}
205 
206 	if (flags_attr) {
207 		flags = nla_get_bitfield32(flags_attr);
208 	} else {
209 		flags.selector = historic_mask;
210 		flags.value = qopt_flags & historic_mask;
211 	}
212 
213 	*p_flags = flags;
214 	*p_userbits = qopt_flags & ~historic_mask;
215 	return 0;
216 }
217 
red_validate_flags(unsigned char flags,struct netlink_ext_ack * extack)218 static inline int red_validate_flags(unsigned char flags,
219 				     struct netlink_ext_ack *extack)
220 {
221 	if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) {
222 		NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN");
223 		return -EINVAL;
224 	}
225 
226 	return 0;
227 }
228 
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)229 static inline void red_set_parms(struct red_parms *p,
230 				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
231 				 u8 Scell_log, u8 *stab, u32 max_P)
232 {
233 	int delta = qth_max - qth_min;
234 	u32 max_p_delta;
235 
236 	p->qth_min	= qth_min << Wlog;
237 	p->qth_max	= qth_max << Wlog;
238 	p->Wlog		= Wlog;
239 	p->Plog		= Plog;
240 	if (delta <= 0)
241 		delta = 1;
242 	p->qth_delta	= delta;
243 	if (!max_P) {
244 		max_P = red_maxp(Plog);
245 		max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */
246 	}
247 	p->max_P = max_P;
248 	max_p_delta = max_P / delta;
249 	max_p_delta = max(max_p_delta, 1U);
250 	p->max_P_reciprocal  = reciprocal_value(max_p_delta);
251 
252 	/* RED Adaptative target :
253 	 * [min_th + 0.4*(min_th - max_th),
254 	 *  min_th + 0.6*(min_th - max_th)].
255 	 */
256 	delta /= 5;
257 	p->target_min = qth_min + 2*delta;
258 	p->target_max = qth_min + 3*delta;
259 
260 	p->Scell_log	= Scell_log;
261 	p->Scell_max	= (255 << Scell_log);
262 
263 	if (stab)
264 		memcpy(p->Stab, stab, sizeof(p->Stab));
265 }
266 
red_is_idling(const struct red_vars * v)267 static inline int red_is_idling(const struct red_vars *v)
268 {
269 	return v->qidlestart != 0;
270 }
271 
red_start_of_idle_period(struct red_vars * v)272 static inline void red_start_of_idle_period(struct red_vars *v)
273 {
274 	v->qidlestart = ktime_get();
275 }
276 
red_end_of_idle_period(struct red_vars * v)277 static inline void red_end_of_idle_period(struct red_vars *v)
278 {
279 	v->qidlestart = 0;
280 }
281 
red_restart(struct red_vars * v)282 static inline void red_restart(struct red_vars *v)
283 {
284 	red_end_of_idle_period(v);
285 	v->qavg = 0;
286 	v->qcount = -1;
287 }
288 
red_calc_qavg_from_idle_time(const struct red_parms * p,const struct red_vars * v)289 static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
290 							 const struct red_vars *v)
291 {
292 	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
293 	long us_idle = min_t(s64, delta, p->Scell_max);
294 	int  shift;
295 
296 	/*
297 	 * The problem: ideally, average length queue recalculation should
298 	 * be done over constant clock intervals. This is too expensive, so
299 	 * that the calculation is driven by outgoing packets.
300 	 * When the queue is idle we have to model this clock by hand.
301 	 *
302 	 * SF+VJ proposed to "generate":
303 	 *
304 	 *	m = idletime / (average_pkt_size / bandwidth)
305 	 *
306 	 * dummy packets as a burst after idle time, i.e.
307 	 *
308 	 * 	v->qavg *= (1-W)^m
309 	 *
310 	 * This is an apparently overcomplicated solution (f.e. we have to
311 	 * precompute a table to make this calculation in reasonable time)
312 	 * I believe that a simpler model may be used here,
313 	 * but it is field for experiments.
314 	 */
315 
316 	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
317 
318 	if (shift)
319 		return v->qavg >> shift;
320 	else {
321 		/* Approximate initial part of exponent with linear function:
322 		 *
323 		 * 	(1-W)^m ~= 1-mW + ...
324 		 *
325 		 * Seems, it is the best solution to
326 		 * problem of too coarse exponent tabulation.
327 		 */
328 		us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
329 
330 		if (us_idle < (v->qavg >> 1))
331 			return v->qavg - us_idle;
332 		else
333 			return v->qavg >> 1;
334 	}
335 }
336 
red_calc_qavg_no_idle_time(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)337 static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
338 						       const struct red_vars *v,
339 						       unsigned int backlog)
340 {
341 	/*
342 	 * NOTE: v->qavg is fixed point number with point at Wlog.
343 	 * The formula below is equvalent to floating point
344 	 * version:
345 	 *
346 	 * 	qavg = qavg*(1-W) + backlog*W;
347 	 *
348 	 * --ANK (980924)
349 	 */
350 	return v->qavg + (backlog - (v->qavg >> p->Wlog));
351 }
352 
red_calc_qavg(const struct red_parms * p,const struct red_vars * v,unsigned int backlog)353 static inline unsigned long red_calc_qavg(const struct red_parms *p,
354 					  const struct red_vars *v,
355 					  unsigned int backlog)
356 {
357 	if (!red_is_idling(v))
358 		return red_calc_qavg_no_idle_time(p, v, backlog);
359 	else
360 		return red_calc_qavg_from_idle_time(p, v);
361 }
362 
363 
red_random(const struct red_parms * p)364 static inline u32 red_random(const struct red_parms *p)
365 {
366 	return reciprocal_divide(get_random_u32(), p->max_P_reciprocal);
367 }
368 
red_mark_probability(const struct red_parms * p,const struct red_vars * v,unsigned long qavg)369 static inline int red_mark_probability(const struct red_parms *p,
370 				       const struct red_vars *v,
371 				       unsigned long qavg)
372 {
373 	/* The formula used below causes questions.
374 
375 	   OK. qR is random number in the interval
376 		(0..1/max_P)*(qth_max-qth_min)
377 	   i.e. 0..(2^Plog). If we used floating point
378 	   arithmetics, it would be: (2^Plog)*rnd_num,
379 	   where rnd_num is less 1.
380 
381 	   Taking into account, that qavg have fixed
382 	   point at Wlog, two lines
383 	   below have the following floating point equivalent:
384 
385 	   max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
386 
387 	   Any questions? --ANK (980924)
388 	 */
389 	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
390 }
391 
392 enum {
393 	RED_BELOW_MIN_THRESH,
394 	RED_BETWEEN_TRESH,
395 	RED_ABOVE_MAX_TRESH,
396 };
397 
red_cmp_thresh(const struct red_parms * p,unsigned long qavg)398 static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
399 {
400 	if (qavg < p->qth_min)
401 		return RED_BELOW_MIN_THRESH;
402 	else if (qavg >= p->qth_max)
403 		return RED_ABOVE_MAX_TRESH;
404 	else
405 		return RED_BETWEEN_TRESH;
406 }
407 
408 enum {
409 	RED_DONT_MARK,
410 	RED_PROB_MARK,
411 	RED_HARD_MARK,
412 };
413 
red_action(const struct red_parms * p,struct red_vars * v,unsigned long qavg)414 static inline int red_action(const struct red_parms *p,
415 			     struct red_vars *v,
416 			     unsigned long qavg)
417 {
418 	switch (red_cmp_thresh(p, qavg)) {
419 		case RED_BELOW_MIN_THRESH:
420 			v->qcount = -1;
421 			return RED_DONT_MARK;
422 
423 		case RED_BETWEEN_TRESH:
424 			if (++v->qcount) {
425 				if (red_mark_probability(p, v, qavg)) {
426 					v->qcount = 0;
427 					v->qR = red_random(p);
428 					return RED_PROB_MARK;
429 				}
430 			} else
431 				v->qR = red_random(p);
432 
433 			return RED_DONT_MARK;
434 
435 		case RED_ABOVE_MAX_TRESH:
436 			v->qcount = -1;
437 			return RED_HARD_MARK;
438 	}
439 
440 	BUG();
441 	return RED_DONT_MARK;
442 }
443 
red_adaptative_algo(struct red_parms * p,struct red_vars * v)444 static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
445 {
446 	unsigned long qavg;
447 	u32 max_p_delta;
448 
449 	qavg = v->qavg;
450 	if (red_is_idling(v))
451 		qavg = red_calc_qavg_from_idle_time(p, v);
452 
453 	/* v->qavg is fixed point number with point at Wlog */
454 	qavg >>= p->Wlog;
455 
456 	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
457 		p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
458 	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
459 		p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */
460 
461 	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
462 	max_p_delta = max(max_p_delta, 1U);
463 	p->max_P_reciprocal = reciprocal_value(max_p_delta);
464 }
465 #endif
466