1 #ifndef __NET_SCHED_CODEL_H 2 #define __NET_SCHED_CODEL_H 3 4 /* 5 * Codel - The Controlled-Delay Active Queue Management algorithm 6 * 7 * Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com> 8 * Copyright (C) 2011-2012 Van Jacobson <van@pollere.net> 9 * Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net> 10 * Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com> 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions, and the following disclaimer, 17 * without modification. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 3. The names of the authors may not be used to endorse or promote products 22 * derived from this software without specific prior written permission. 23 * 24 * Alternatively, provided that this notice is retained in full, this 25 * software may be distributed under the terms of the GNU General 26 * Public License ("GPL") version 2, in which case the provisions of the 27 * GPL apply INSTEAD OF those given above. 28 * 29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 30 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 31 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 32 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 33 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 34 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 40 * DAMAGE. 41 * 42 */ 43 44 #include <linux/types.h> 45 #include <linux/ktime.h> 46 #include <linux/skbuff.h> 47 #include <net/pkt_sched.h> 48 #include <net/inet_ecn.h> 49 50 /* Controlling Queue Delay (CoDel) algorithm 51 * ========================================= 52 * Source : Kathleen Nichols and Van Jacobson 53 * http://queue.acm.org/detail.cfm?id=2209336 54 * 55 * Implemented on linux by Dave Taht and Eric Dumazet 56 */ 57 58 59 /* CoDel uses a 1024 nsec clock, encoded in u32 60 * This gives a range of 2199 seconds, because of signed compares 61 */ 62 typedef u32 codel_time_t; 63 typedef s32 codel_tdiff_t; 64 #define CODEL_SHIFT 10 65 #define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT) 66 67 static inline codel_time_t codel_get_time(void) 68 { 69 u64 ns = ktime_get_ns(); 70 71 return ns >> CODEL_SHIFT; 72 } 73 74 /* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia: 75 * https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution 76 * codel_time_after(a,b) returns true if the time a is after time b. 77 */ 78 #define codel_time_after(a, b) \ 79 (typecheck(codel_time_t, a) && \ 80 typecheck(codel_time_t, b) && \ 81 ((s32)((a) - (b)) > 0)) 82 #define codel_time_before(a, b) codel_time_after(b, a) 83 84 #define codel_time_after_eq(a, b) \ 85 (typecheck(codel_time_t, a) && \ 86 typecheck(codel_time_t, b) && \ 87 ((s32)((a) - (b)) >= 0)) 88 #define codel_time_before_eq(a, b) codel_time_after_eq(b, a) 89 90 /* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */ 91 struct codel_skb_cb { 92 codel_time_t enqueue_time; 93 }; 94 95 static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb) 96 { 97 qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb)); 98 return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data; 99 } 100 101 static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb) 102 { 103 return get_codel_cb(skb)->enqueue_time; 104 } 105 106 static void codel_set_enqueue_time(struct sk_buff *skb) 107 { 108 get_codel_cb(skb)->enqueue_time = codel_get_time(); 109 } 110 111 static inline u32 codel_time_to_us(codel_time_t val) 112 { 113 u64 valns = ((u64)val << CODEL_SHIFT); 114 115 do_div(valns, NSEC_PER_USEC); 116 return (u32)valns; 117 } 118 119 /** 120 * struct codel_params - contains codel parameters 121 * @target: target queue size (in time units) 122 * @ce_threshold: threshold for marking packets with ECN CE 123 * @interval: width of moving time window 124 * @mtu: device mtu, or minimal queue backlog in bytes. 125 * @ecn: is Explicit Congestion Notification enabled 126 */ 127 struct codel_params { 128 codel_time_t target; 129 codel_time_t ce_threshold; 130 codel_time_t interval; 131 u32 mtu; 132 bool ecn; 133 }; 134 135 /** 136 * struct codel_vars - contains codel variables 137 * @count: how many drops we've done since the last time we 138 * entered dropping state 139 * @lastcount: count at entry to dropping state 140 * @dropping: set to true if in dropping state 141 * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1 142 * @first_above_time: when we went (or will go) continuously above target 143 * for interval 144 * @drop_next: time to drop next packet, or when we dropped last 145 * @ldelay: sojourn time of last dequeued packet 146 */ 147 struct codel_vars { 148 u32 count; 149 u32 lastcount; 150 bool dropping; 151 u16 rec_inv_sqrt; 152 codel_time_t first_above_time; 153 codel_time_t drop_next; 154 codel_time_t ldelay; 155 }; 156 157 #define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */ 158 /* needed shift to get a Q0.32 number from rec_inv_sqrt */ 159 #define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS) 160 161 /** 162 * struct codel_stats - contains codel shared variables and stats 163 * @maxpacket: largest packet we've seen so far 164 * @drop_count: temp count of dropped packets in dequeue() 165 * @drop_len: bytes of dropped packets in dequeue() 166 * ecn_mark: number of packets we ECN marked instead of dropping 167 * ce_mark: number of packets CE marked because sojourn time was above ce_threshold 168 */ 169 struct codel_stats { 170 u32 maxpacket; 171 u32 drop_count; 172 u32 drop_len; 173 u32 ecn_mark; 174 u32 ce_mark; 175 }; 176 177 #define CODEL_DISABLED_THRESHOLD INT_MAX 178 179 static void codel_params_init(struct codel_params *params, 180 const struct Qdisc *sch) 181 { 182 params->interval = MS2TIME(100); 183 params->target = MS2TIME(5); 184 params->mtu = psched_mtu(qdisc_dev(sch)); 185 params->ce_threshold = CODEL_DISABLED_THRESHOLD; 186 params->ecn = false; 187 } 188 189 static void codel_vars_init(struct codel_vars *vars) 190 { 191 memset(vars, 0, sizeof(*vars)); 192 } 193 194 static void codel_stats_init(struct codel_stats *stats) 195 { 196 stats->maxpacket = 0; 197 } 198 199 /* 200 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots 201 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2) 202 * 203 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32 204 */ 205 static void codel_Newton_step(struct codel_vars *vars) 206 { 207 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT; 208 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32; 209 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2); 210 211 val >>= 2; /* avoid overflow in following multiply */ 212 val = (val * invsqrt) >> (32 - 2 + 1); 213 214 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT; 215 } 216 217 /* 218 * CoDel control_law is t + interval/sqrt(count) 219 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid 220 * both sqrt() and divide operation. 221 */ 222 static codel_time_t codel_control_law(codel_time_t t, 223 codel_time_t interval, 224 u32 rec_inv_sqrt) 225 { 226 return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT); 227 } 228 229 static bool codel_should_drop(const struct sk_buff *skb, 230 struct Qdisc *sch, 231 struct codel_vars *vars, 232 struct codel_params *params, 233 struct codel_stats *stats, 234 codel_time_t now) 235 { 236 bool ok_to_drop; 237 238 if (!skb) { 239 vars->first_above_time = 0; 240 return false; 241 } 242 243 vars->ldelay = now - codel_get_enqueue_time(skb); 244 sch->qstats.backlog -= qdisc_pkt_len(skb); 245 246 if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket)) 247 stats->maxpacket = qdisc_pkt_len(skb); 248 249 if (codel_time_before(vars->ldelay, params->target) || 250 sch->qstats.backlog <= params->mtu) { 251 /* went below - stay below for at least interval */ 252 vars->first_above_time = 0; 253 return false; 254 } 255 ok_to_drop = false; 256 if (vars->first_above_time == 0) { 257 /* just went above from below. If we stay above 258 * for at least interval we'll say it's ok to drop 259 */ 260 vars->first_above_time = now + params->interval; 261 } else if (codel_time_after(now, vars->first_above_time)) { 262 ok_to_drop = true; 263 } 264 return ok_to_drop; 265 } 266 267 typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars, 268 struct Qdisc *sch); 269 270 static struct sk_buff *codel_dequeue(struct Qdisc *sch, 271 struct codel_params *params, 272 struct codel_vars *vars, 273 struct codel_stats *stats, 274 codel_skb_dequeue_t dequeue_func) 275 { 276 struct sk_buff *skb = dequeue_func(vars, sch); 277 codel_time_t now; 278 bool drop; 279 280 if (!skb) { 281 vars->dropping = false; 282 return skb; 283 } 284 now = codel_get_time(); 285 drop = codel_should_drop(skb, sch, vars, params, stats, now); 286 if (vars->dropping) { 287 if (!drop) { 288 /* sojourn time below target - leave dropping state */ 289 vars->dropping = false; 290 } else if (codel_time_after_eq(now, vars->drop_next)) { 291 /* It's time for the next drop. Drop the current 292 * packet and dequeue the next. The dequeue might 293 * take us out of dropping state. 294 * If not, schedule the next drop. 295 * A large backlog might result in drop rates so high 296 * that the next drop should happen now, 297 * hence the while loop. 298 */ 299 while (vars->dropping && 300 codel_time_after_eq(now, vars->drop_next)) { 301 vars->count++; /* dont care of possible wrap 302 * since there is no more divide 303 */ 304 codel_Newton_step(vars); 305 if (params->ecn && INET_ECN_set_ce(skb)) { 306 stats->ecn_mark++; 307 vars->drop_next = 308 codel_control_law(vars->drop_next, 309 params->interval, 310 vars->rec_inv_sqrt); 311 goto end; 312 } 313 stats->drop_len += qdisc_pkt_len(skb); 314 qdisc_drop(skb, sch); 315 stats->drop_count++; 316 skb = dequeue_func(vars, sch); 317 if (!codel_should_drop(skb, sch, 318 vars, params, stats, now)) { 319 /* leave dropping state */ 320 vars->dropping = false; 321 } else { 322 /* and schedule the next drop */ 323 vars->drop_next = 324 codel_control_law(vars->drop_next, 325 params->interval, 326 vars->rec_inv_sqrt); 327 } 328 } 329 } 330 } else if (drop) { 331 u32 delta; 332 333 if (params->ecn && INET_ECN_set_ce(skb)) { 334 stats->ecn_mark++; 335 } else { 336 stats->drop_len += qdisc_pkt_len(skb); 337 qdisc_drop(skb, sch); 338 stats->drop_count++; 339 340 skb = dequeue_func(vars, sch); 341 drop = codel_should_drop(skb, sch, vars, params, 342 stats, now); 343 } 344 vars->dropping = true; 345 /* if min went above target close to when we last went below it 346 * assume that the drop rate that controlled the queue on the 347 * last cycle is a good starting point to control it now. 348 */ 349 delta = vars->count - vars->lastcount; 350 if (delta > 1 && 351 codel_time_before(now - vars->drop_next, 352 16 * params->interval)) { 353 vars->count = delta; 354 /* we dont care if rec_inv_sqrt approximation 355 * is not very precise : 356 * Next Newton steps will correct it quadratically. 357 */ 358 codel_Newton_step(vars); 359 } else { 360 vars->count = 1; 361 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; 362 } 363 vars->lastcount = vars->count; 364 vars->drop_next = codel_control_law(now, params->interval, 365 vars->rec_inv_sqrt); 366 } 367 end: 368 if (skb && codel_time_after(vars->ldelay, params->ce_threshold) && 369 INET_ECN_set_ce(skb)) 370 stats->ce_mark++; 371 return skb; 372 } 373 #endif 374