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 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 #include <linux/reciprocal_div.h> 50 51 /* Controlling Queue Delay (CoDel) algorithm 52 * ========================================= 53 * Source : Kathleen Nichols and Van Jacobson 54 * http://queue.acm.org/detail.cfm?id=2209336 55 * 56 * Implemented on linux by Dave Taht and Eric Dumazet 57 */ 58 59 60 /* CoDel uses a 1024 nsec clock, encoded in u32 61 * This gives a range of 2199 seconds, because of signed compares 62 */ 63 typedef u32 codel_time_t; 64 typedef s32 codel_tdiff_t; 65 #define CODEL_SHIFT 10 66 #define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT) 67 68 static inline codel_time_t codel_get_time(void) 69 { 70 u64 ns = ktime_to_ns(ktime_get()); 71 72 return ns >> CODEL_SHIFT; 73 } 74 75 /* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia: 76 * https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution 77 * codel_time_after(a,b) returns true if the time a is after time b. 78 */ 79 #define codel_time_after(a, b) \ 80 (typecheck(codel_time_t, a) && \ 81 typecheck(codel_time_t, b) && \ 82 ((s32)((a) - (b)) > 0)) 83 #define codel_time_before(a, b) codel_time_after(b, a) 84 85 #define codel_time_after_eq(a, b) \ 86 (typecheck(codel_time_t, a) && \ 87 typecheck(codel_time_t, b) && \ 88 ((s32)((a) - (b)) >= 0)) 89 #define codel_time_before_eq(a, b) codel_time_after_eq(b, a) 90 91 /* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */ 92 struct codel_skb_cb { 93 codel_time_t enqueue_time; 94 }; 95 96 static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb) 97 { 98 qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb)); 99 return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data; 100 } 101 102 static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb) 103 { 104 return get_codel_cb(skb)->enqueue_time; 105 } 106 107 static void codel_set_enqueue_time(struct sk_buff *skb) 108 { 109 get_codel_cb(skb)->enqueue_time = codel_get_time(); 110 } 111 112 static inline u32 codel_time_to_us(codel_time_t val) 113 { 114 u64 valns = ((u64)val << CODEL_SHIFT); 115 116 do_div(valns, NSEC_PER_USEC); 117 return (u32)valns; 118 } 119 120 /** 121 * struct codel_params - contains codel parameters 122 * @target: target queue size (in time units) 123 * @interval: width of moving time window 124 * @ecn: is Explicit Congestion Notification enabled 125 */ 126 struct codel_params { 127 codel_time_t target; 128 codel_time_t interval; 129 bool ecn; 130 }; 131 132 /** 133 * struct codel_vars - contains codel variables 134 * @count: how many drops we've done since the last time we 135 * entered dropping state 136 * @lastcount: count at entry to dropping state 137 * @dropping: set to true if in dropping state 138 * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1 139 * @first_above_time: when we went (or will go) continuously above target 140 * for interval 141 * @drop_next: time to drop next packet, or when we dropped last 142 * @ldelay: sojourn time of last dequeued packet 143 */ 144 struct codel_vars { 145 u32 count; 146 u32 lastcount; 147 bool dropping; 148 u16 rec_inv_sqrt; 149 codel_time_t first_above_time; 150 codel_time_t drop_next; 151 codel_time_t ldelay; 152 }; 153 154 #define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */ 155 /* needed shift to get a Q0.32 number from rec_inv_sqrt */ 156 #define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS) 157 158 /** 159 * struct codel_stats - contains codel shared variables and stats 160 * @maxpacket: largest packet we've seen so far 161 * @drop_count: temp count of dropped packets in dequeue() 162 * ecn_mark: number of packets we ECN marked instead of dropping 163 */ 164 struct codel_stats { 165 u32 maxpacket; 166 u32 drop_count; 167 u32 ecn_mark; 168 }; 169 170 static void codel_params_init(struct codel_params *params) 171 { 172 params->interval = MS2TIME(100); 173 params->target = MS2TIME(5); 174 params->ecn = false; 175 } 176 177 static void codel_vars_init(struct codel_vars *vars) 178 { 179 memset(vars, 0, sizeof(*vars)); 180 } 181 182 static void codel_stats_init(struct codel_stats *stats) 183 { 184 stats->maxpacket = 256; 185 } 186 187 /* 188 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots 189 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2) 190 * 191 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32 192 */ 193 static void codel_Newton_step(struct codel_vars *vars) 194 { 195 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT; 196 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32; 197 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2); 198 199 val >>= 2; /* avoid overflow in following multiply */ 200 val = (val * invsqrt) >> (32 - 2 + 1); 201 202 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT; 203 } 204 205 /* 206 * CoDel control_law is t + interval/sqrt(count) 207 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid 208 * both sqrt() and divide operation. 209 */ 210 static codel_time_t codel_control_law(codel_time_t t, 211 codel_time_t interval, 212 u32 rec_inv_sqrt) 213 { 214 return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT); 215 } 216 217 218 static bool codel_should_drop(const struct sk_buff *skb, 219 struct Qdisc *sch, 220 struct codel_vars *vars, 221 struct codel_params *params, 222 struct codel_stats *stats, 223 codel_time_t now) 224 { 225 bool ok_to_drop; 226 227 if (!skb) { 228 vars->first_above_time = 0; 229 return false; 230 } 231 232 vars->ldelay = now - codel_get_enqueue_time(skb); 233 sch->qstats.backlog -= qdisc_pkt_len(skb); 234 235 if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket)) 236 stats->maxpacket = qdisc_pkt_len(skb); 237 238 if (codel_time_before(vars->ldelay, params->target) || 239 sch->qstats.backlog <= stats->maxpacket) { 240 /* went below - stay below for at least interval */ 241 vars->first_above_time = 0; 242 return false; 243 } 244 ok_to_drop = false; 245 if (vars->first_above_time == 0) { 246 /* just went above from below. If we stay above 247 * for at least interval we'll say it's ok to drop 248 */ 249 vars->first_above_time = now + params->interval; 250 } else if (codel_time_after(now, vars->first_above_time)) { 251 ok_to_drop = true; 252 } 253 return ok_to_drop; 254 } 255 256 typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars, 257 struct Qdisc *sch); 258 259 static struct sk_buff *codel_dequeue(struct Qdisc *sch, 260 struct codel_params *params, 261 struct codel_vars *vars, 262 struct codel_stats *stats, 263 codel_skb_dequeue_t dequeue_func) 264 { 265 struct sk_buff *skb = dequeue_func(vars, sch); 266 codel_time_t now; 267 bool drop; 268 269 if (!skb) { 270 vars->dropping = false; 271 return skb; 272 } 273 now = codel_get_time(); 274 drop = codel_should_drop(skb, sch, vars, params, stats, now); 275 if (vars->dropping) { 276 if (!drop) { 277 /* sojourn time below target - leave dropping state */ 278 vars->dropping = false; 279 } else if (codel_time_after_eq(now, vars->drop_next)) { 280 /* It's time for the next drop. Drop the current 281 * packet and dequeue the next. The dequeue might 282 * take us out of dropping state. 283 * If not, schedule the next drop. 284 * A large backlog might result in drop rates so high 285 * that the next drop should happen now, 286 * hence the while loop. 287 */ 288 while (vars->dropping && 289 codel_time_after_eq(now, vars->drop_next)) { 290 vars->count++; /* dont care of possible wrap 291 * since there is no more divide 292 */ 293 codel_Newton_step(vars); 294 if (params->ecn && INET_ECN_set_ce(skb)) { 295 stats->ecn_mark++; 296 vars->drop_next = 297 codel_control_law(vars->drop_next, 298 params->interval, 299 vars->rec_inv_sqrt); 300 goto end; 301 } 302 qdisc_drop(skb, sch); 303 stats->drop_count++; 304 skb = dequeue_func(vars, sch); 305 if (!codel_should_drop(skb, sch, 306 vars, params, stats, now)) { 307 /* leave dropping state */ 308 vars->dropping = false; 309 } else { 310 /* and schedule the next drop */ 311 vars->drop_next = 312 codel_control_law(vars->drop_next, 313 params->interval, 314 vars->rec_inv_sqrt); 315 } 316 } 317 } 318 } else if (drop) { 319 u32 delta; 320 321 if (params->ecn && INET_ECN_set_ce(skb)) { 322 stats->ecn_mark++; 323 } else { 324 qdisc_drop(skb, sch); 325 stats->drop_count++; 326 327 skb = dequeue_func(vars, sch); 328 drop = codel_should_drop(skb, sch, vars, params, 329 stats, now); 330 } 331 vars->dropping = true; 332 /* if min went above target close to when we last went below it 333 * assume that the drop rate that controlled the queue on the 334 * last cycle is a good starting point to control it now. 335 */ 336 delta = vars->count - vars->lastcount; 337 if (delta > 1 && 338 codel_time_before(now - vars->drop_next, 339 16 * params->interval)) { 340 vars->count = delta; 341 /* we dont care if rec_inv_sqrt approximation 342 * is not very precise : 343 * Next Newton steps will correct it quadratically. 344 */ 345 codel_Newton_step(vars); 346 } else { 347 vars->count = 1; 348 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; 349 } 350 vars->lastcount = vars->count; 351 vars->drop_next = codel_control_law(now, params->interval, 352 vars->rec_inv_sqrt); 353 } 354 end: 355 return skb; 356 } 357 #endif 358