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 #include <linux/reciprocal_div.h> 9 10 /* Random Early Detection (RED) algorithm. 11 ======================================= 12 13 Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways 14 for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking. 15 16 This file codes a "divisionless" version of RED algorithm 17 as written down in Fig.17 of the paper. 18 19 Short description. 20 ------------------ 21 22 When a new packet arrives we calculate the average queue length: 23 24 avg = (1-W)*avg + W*current_queue_len, 25 26 W is the filter time constant (chosen as 2^(-Wlog)), it controls 27 the inertia of the algorithm. To allow larger bursts, W should be 28 decreased. 29 30 if (avg > th_max) -> packet marked (dropped). 31 if (avg < th_min) -> packet passes. 32 if (th_min < avg < th_max) we calculate probability: 33 34 Pb = max_P * (avg - th_min)/(th_max-th_min) 35 36 and mark (drop) packet with this probability. 37 Pb changes from 0 (at avg==th_min) to max_P (avg==th_max). 38 max_P should be small (not 1), usually 0.01..0.02 is good value. 39 40 max_P is chosen as a number, so that max_P/(th_max-th_min) 41 is a negative power of two in order arithmetics to contain 42 only shifts. 43 44 45 Parameters, settable by user: 46 ----------------------------- 47 48 qth_min - bytes (should be < qth_max/2) 49 qth_max - bytes (should be at least 2*qth_min and less limit) 50 Wlog - bits (<32) log(1/W). 51 Plog - bits (<32) 52 53 Plog is related to max_P by formula: 54 55 max_P = (qth_max-qth_min)/2^Plog; 56 57 F.e. if qth_max=128K and qth_min=32K, then Plog=22 58 corresponds to max_P=0.02 59 60 Scell_log 61 Stab 62 63 Lookup table for log((1-W)^(t/t_ave). 64 65 66 NOTES: 67 68 Upper bound on W. 69 ----------------- 70 71 If you want to allow bursts of L packets of size S, 72 you should choose W: 73 74 L + 1 - th_min/S < (1-(1-W)^L)/W 75 76 th_min/S = 32 th_min/S = 4 77 78 log(W) L 79 -1 33 80 -2 35 81 -3 39 82 -4 46 83 -5 57 84 -6 75 85 -7 101 86 -8 135 87 -9 190 88 etc. 89 */ 90 91 /* 92 * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM 93 * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001 94 * 95 * Every 500 ms: 96 * if (avg > target and max_p <= 0.5) 97 * increase max_p : max_p += alpha; 98 * else if (avg < target and max_p >= 0.01) 99 * decrease max_p : max_p *= beta; 100 * 101 * target :[qth_min + 0.4*(qth_min - qth_max), 102 * qth_min + 0.6*(qth_min - qth_max)]. 103 * alpha : min(0.01, max_p / 4) 104 * beta : 0.9 105 * max_P is a Q0.32 fixed point number (with 32 bits mantissa) 106 * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ] 107 */ 108 #define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100)) 109 110 #define MAX_P_MIN (1 * RED_ONE_PERCENT) 111 #define MAX_P_MAX (50 * RED_ONE_PERCENT) 112 #define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4) 113 114 #define RED_STAB_SIZE 256 115 #define RED_STAB_MASK (RED_STAB_SIZE - 1) 116 117 struct red_stats { 118 u32 prob_drop; /* Early probability drops */ 119 u32 prob_mark; /* Early probability marks */ 120 u32 forced_drop; /* Forced drops, qavg > max_thresh */ 121 u32 forced_mark; /* Forced marks, qavg > max_thresh */ 122 u32 pdrop; /* Drops due to queue limits */ 123 u32 other; /* Drops due to drop() calls */ 124 }; 125 126 struct red_parms { 127 /* Parameters */ 128 u32 qth_min; /* Min avg length threshold: Wlog scaled */ 129 u32 qth_max; /* Max avg length threshold: Wlog scaled */ 130 u32 Scell_max; 131 u32 max_P; /* probability, [0 .. 1.0] 32 scaled */ 132 u32 max_P_reciprocal; /* reciprocal_value(max_P / qth_delta) */ 133 u32 qth_delta; /* max_th - min_th */ 134 u32 target_min; /* min_th + 0.4*(max_th - min_th) */ 135 u32 target_max; /* min_th + 0.6*(max_th - min_th) */ 136 u8 Scell_log; 137 u8 Wlog; /* log(W) */ 138 u8 Plog; /* random number bits */ 139 u8 Stab[RED_STAB_SIZE]; 140 }; 141 142 struct red_vars { 143 /* Variables */ 144 int qcount; /* Number of packets since last random 145 number generation */ 146 u32 qR; /* Cached random number */ 147 148 unsigned long qavg; /* Average queue length: Wlog scaled */ 149 ktime_t qidlestart; /* Start of current idle period */ 150 }; 151 152 static inline u32 red_maxp(u8 Plog) 153 { 154 return Plog < 32 ? (~0U >> Plog) : ~0U; 155 } 156 157 static inline void red_set_vars(struct red_vars *v) 158 { 159 /* Reset average queue length, the value is strictly bound 160 * to the parameters below, reseting hurts a bit but leaving 161 * it might result in an unreasonable qavg for a while. --TGR 162 */ 163 v->qavg = 0; 164 165 v->qcount = -1; 166 } 167 168 static inline void red_set_parms(struct red_parms *p, 169 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog, 170 u8 Scell_log, u8 *stab, u32 max_P) 171 { 172 int delta = qth_max - qth_min; 173 u32 max_p_delta; 174 175 p->qth_min = qth_min << Wlog; 176 p->qth_max = qth_max << Wlog; 177 p->Wlog = Wlog; 178 p->Plog = Plog; 179 if (delta < 0) 180 delta = 1; 181 p->qth_delta = delta; 182 if (!max_P) { 183 max_P = red_maxp(Plog); 184 max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ 185 } 186 p->max_P = max_P; 187 max_p_delta = max_P / delta; 188 max_p_delta = max(max_p_delta, 1U); 189 p->max_P_reciprocal = reciprocal_value(max_p_delta); 190 191 /* RED Adaptative target : 192 * [min_th + 0.4*(min_th - max_th), 193 * min_th + 0.6*(min_th - max_th)]. 194 */ 195 delta /= 5; 196 p->target_min = qth_min + 2*delta; 197 p->target_max = qth_min + 3*delta; 198 199 p->Scell_log = Scell_log; 200 p->Scell_max = (255 << Scell_log); 201 202 memcpy(p->Stab, stab, sizeof(p->Stab)); 203 } 204 205 static inline int red_is_idling(const struct red_vars *v) 206 { 207 return v->qidlestart.tv64 != 0; 208 } 209 210 static inline void red_start_of_idle_period(struct red_vars *v) 211 { 212 v->qidlestart = ktime_get(); 213 } 214 215 static inline void red_end_of_idle_period(struct red_vars *v) 216 { 217 v->qidlestart.tv64 = 0; 218 } 219 220 static inline void red_restart(struct red_vars *v) 221 { 222 red_end_of_idle_period(v); 223 v->qavg = 0; 224 v->qcount = -1; 225 } 226 227 static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p, 228 const struct red_vars *v) 229 { 230 s64 delta = ktime_us_delta(ktime_get(), v->qidlestart); 231 long us_idle = min_t(s64, delta, p->Scell_max); 232 int shift; 233 234 /* 235 * The problem: ideally, average length queue recalcultion should 236 * be done over constant clock intervals. This is too expensive, so 237 * that the calculation is driven by outgoing packets. 238 * When the queue is idle we have to model this clock by hand. 239 * 240 * SF+VJ proposed to "generate": 241 * 242 * m = idletime / (average_pkt_size / bandwidth) 243 * 244 * dummy packets as a burst after idle time, i.e. 245 * 246 * p->qavg *= (1-W)^m 247 * 248 * This is an apparently overcomplicated solution (f.e. we have to 249 * precompute a table to make this calculation in reasonable time) 250 * I believe that a simpler model may be used here, 251 * but it is field for experiments. 252 */ 253 254 shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK]; 255 256 if (shift) 257 return v->qavg >> shift; 258 else { 259 /* Approximate initial part of exponent with linear function: 260 * 261 * (1-W)^m ~= 1-mW + ... 262 * 263 * Seems, it is the best solution to 264 * problem of too coarse exponent tabulation. 265 */ 266 us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log; 267 268 if (us_idle < (v->qavg >> 1)) 269 return v->qavg - us_idle; 270 else 271 return v->qavg >> 1; 272 } 273 } 274 275 static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p, 276 const struct red_vars *v, 277 unsigned int backlog) 278 { 279 /* 280 * NOTE: p->qavg is fixed point number with point at Wlog. 281 * The formula below is equvalent to floating point 282 * version: 283 * 284 * qavg = qavg*(1-W) + backlog*W; 285 * 286 * --ANK (980924) 287 */ 288 return v->qavg + (backlog - (v->qavg >> p->Wlog)); 289 } 290 291 static inline unsigned long red_calc_qavg(const struct red_parms *p, 292 const struct red_vars *v, 293 unsigned int backlog) 294 { 295 if (!red_is_idling(v)) 296 return red_calc_qavg_no_idle_time(p, v, backlog); 297 else 298 return red_calc_qavg_from_idle_time(p, v); 299 } 300 301 302 static inline u32 red_random(const struct red_parms *p) 303 { 304 return reciprocal_divide(net_random(), p->max_P_reciprocal); 305 } 306 307 static inline int red_mark_probability(const struct red_parms *p, 308 const struct red_vars *v, 309 unsigned long qavg) 310 { 311 /* The formula used below causes questions. 312 313 OK. qR is random number in the interval 314 (0..1/max_P)*(qth_max-qth_min) 315 i.e. 0..(2^Plog). If we used floating point 316 arithmetics, it would be: (2^Plog)*rnd_num, 317 where rnd_num is less 1. 318 319 Taking into account, that qavg have fixed 320 point at Wlog, two lines 321 below have the following floating point equivalent: 322 323 max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount 324 325 Any questions? --ANK (980924) 326 */ 327 return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR); 328 } 329 330 enum { 331 RED_BELOW_MIN_THRESH, 332 RED_BETWEEN_TRESH, 333 RED_ABOVE_MAX_TRESH, 334 }; 335 336 static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg) 337 { 338 if (qavg < p->qth_min) 339 return RED_BELOW_MIN_THRESH; 340 else if (qavg >= p->qth_max) 341 return RED_ABOVE_MAX_TRESH; 342 else 343 return RED_BETWEEN_TRESH; 344 } 345 346 enum { 347 RED_DONT_MARK, 348 RED_PROB_MARK, 349 RED_HARD_MARK, 350 }; 351 352 static inline int red_action(const struct red_parms *p, 353 struct red_vars *v, 354 unsigned long qavg) 355 { 356 switch (red_cmp_thresh(p, qavg)) { 357 case RED_BELOW_MIN_THRESH: 358 v->qcount = -1; 359 return RED_DONT_MARK; 360 361 case RED_BETWEEN_TRESH: 362 if (++v->qcount) { 363 if (red_mark_probability(p, v, qavg)) { 364 v->qcount = 0; 365 v->qR = red_random(p); 366 return RED_PROB_MARK; 367 } 368 } else 369 v->qR = red_random(p); 370 371 return RED_DONT_MARK; 372 373 case RED_ABOVE_MAX_TRESH: 374 v->qcount = -1; 375 return RED_HARD_MARK; 376 } 377 378 BUG(); 379 return RED_DONT_MARK; 380 } 381 382 static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v) 383 { 384 unsigned long qavg; 385 u32 max_p_delta; 386 387 qavg = v->qavg; 388 if (red_is_idling(v)) 389 qavg = red_calc_qavg_from_idle_time(p, v); 390 391 /* p->qavg is fixed point number with point at Wlog */ 392 qavg >>= p->Wlog; 393 394 if (qavg > p->target_max && p->max_P <= MAX_P_MAX) 395 p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */ 396 else if (qavg < p->target_min && p->max_P >= MAX_P_MIN) 397 p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */ 398 399 max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta); 400 max_p_delta = max(max_p_delta, 1U); 401 p->max_P_reciprocal = reciprocal_value(max_p_delta); 402 } 403 #endif 404