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 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 * @interval: width of moving time window 123 * @mtu: device mtu, or minimal queue backlog in bytes. 124 * @ecn: is Explicit Congestion Notification enabled 125 */ 126 struct codel_params { 127 codel_time_t target; 128 codel_time_t interval; 129 u32 mtu; 130 bool ecn; 131 }; 132 133 /** 134 * struct codel_vars - contains codel variables 135 * @count: how many drops we've done since the last time we 136 * entered dropping state 137 * @lastcount: count at entry to dropping state 138 * @dropping: set to true if in dropping state 139 * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1 140 * @first_above_time: when we went (or will go) continuously above target 141 * for interval 142 * @drop_next: time to drop next packet, or when we dropped last 143 * @ldelay: sojourn time of last dequeued packet 144 */ 145 struct codel_vars { 146 u32 count; 147 u32 lastcount; 148 bool dropping; 149 u16 rec_inv_sqrt; 150 codel_time_t first_above_time; 151 codel_time_t drop_next; 152 codel_time_t ldelay; 153 }; 154 155 #define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */ 156 /* needed shift to get a Q0.32 number from rec_inv_sqrt */ 157 #define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS) 158 159 /** 160 * struct codel_stats - contains codel shared variables and stats 161 * @maxpacket: largest packet we've seen so far 162 * @drop_count: temp count of dropped packets in dequeue() 163 * ecn_mark: number of packets we ECN marked instead of dropping 164 */ 165 struct codel_stats { 166 u32 maxpacket; 167 u32 drop_count; 168 u32 ecn_mark; 169 }; 170 171 static void codel_params_init(struct codel_params *params, 172 const struct Qdisc *sch) 173 { 174 params->interval = MS2TIME(100); 175 params->target = MS2TIME(5); 176 params->mtu = psched_mtu(qdisc_dev(sch)); 177 params->ecn = false; 178 } 179 180 static void codel_vars_init(struct codel_vars *vars) 181 { 182 memset(vars, 0, sizeof(*vars)); 183 } 184 185 static void codel_stats_init(struct codel_stats *stats) 186 { 187 stats->maxpacket = 0; 188 } 189 190 /* 191 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots 192 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2) 193 * 194 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32 195 */ 196 static void codel_Newton_step(struct codel_vars *vars) 197 { 198 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT; 199 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32; 200 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2); 201 202 val >>= 2; /* avoid overflow in following multiply */ 203 val = (val * invsqrt) >> (32 - 2 + 1); 204 205 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT; 206 } 207 208 /* 209 * CoDel control_law is t + interval/sqrt(count) 210 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid 211 * both sqrt() and divide operation. 212 */ 213 static codel_time_t codel_control_law(codel_time_t t, 214 codel_time_t interval, 215 u32 rec_inv_sqrt) 216 { 217 return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT); 218 } 219 220 static bool codel_should_drop(const struct sk_buff *skb, 221 struct Qdisc *sch, 222 struct codel_vars *vars, 223 struct codel_params *params, 224 struct codel_stats *stats, 225 codel_time_t now) 226 { 227 bool ok_to_drop; 228 229 if (!skb) { 230 vars->first_above_time = 0; 231 return false; 232 } 233 234 vars->ldelay = now - codel_get_enqueue_time(skb); 235 sch->qstats.backlog -= qdisc_pkt_len(skb); 236 237 if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket)) 238 stats->maxpacket = qdisc_pkt_len(skb); 239 240 if (codel_time_before(vars->ldelay, params->target) || 241 sch->qstats.backlog <= params->mtu) { 242 /* went below - stay below for at least interval */ 243 vars->first_above_time = 0; 244 return false; 245 } 246 ok_to_drop = false; 247 if (vars->first_above_time == 0) { 248 /* just went above from below. If we stay above 249 * for at least interval we'll say it's ok to drop 250 */ 251 vars->first_above_time = now + params->interval; 252 } else if (codel_time_after(now, vars->first_above_time)) { 253 ok_to_drop = true; 254 } 255 return ok_to_drop; 256 } 257 258 typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars, 259 struct Qdisc *sch); 260 261 static struct sk_buff *codel_dequeue(struct Qdisc *sch, 262 struct codel_params *params, 263 struct codel_vars *vars, 264 struct codel_stats *stats, 265 codel_skb_dequeue_t dequeue_func) 266 { 267 struct sk_buff *skb = dequeue_func(vars, sch); 268 codel_time_t now; 269 bool drop; 270 271 if (!skb) { 272 vars->dropping = false; 273 return skb; 274 } 275 now = codel_get_time(); 276 drop = codel_should_drop(skb, sch, vars, params, stats, now); 277 if (vars->dropping) { 278 if (!drop) { 279 /* sojourn time below target - leave dropping state */ 280 vars->dropping = false; 281 } else if (codel_time_after_eq(now, vars->drop_next)) { 282 /* It's time for the next drop. Drop the current 283 * packet and dequeue the next. The dequeue might 284 * take us out of dropping state. 285 * If not, schedule the next drop. 286 * A large backlog might result in drop rates so high 287 * that the next drop should happen now, 288 * hence the while loop. 289 */ 290 while (vars->dropping && 291 codel_time_after_eq(now, vars->drop_next)) { 292 vars->count++; /* dont care of possible wrap 293 * since there is no more divide 294 */ 295 codel_Newton_step(vars); 296 if (params->ecn && INET_ECN_set_ce(skb)) { 297 stats->ecn_mark++; 298 vars->drop_next = 299 codel_control_law(vars->drop_next, 300 params->interval, 301 vars->rec_inv_sqrt); 302 goto end; 303 } 304 qdisc_drop(skb, sch); 305 stats->drop_count++; 306 skb = dequeue_func(vars, sch); 307 if (!codel_should_drop(skb, sch, 308 vars, params, stats, now)) { 309 /* leave dropping state */ 310 vars->dropping = false; 311 } else { 312 /* and schedule the next drop */ 313 vars->drop_next = 314 codel_control_law(vars->drop_next, 315 params->interval, 316 vars->rec_inv_sqrt); 317 } 318 } 319 } 320 } else if (drop) { 321 u32 delta; 322 323 if (params->ecn && INET_ECN_set_ce(skb)) { 324 stats->ecn_mark++; 325 } else { 326 qdisc_drop(skb, sch); 327 stats->drop_count++; 328 329 skb = dequeue_func(vars, sch); 330 drop = codel_should_drop(skb, sch, vars, params, 331 stats, now); 332 } 333 vars->dropping = true; 334 /* if min went above target close to when we last went below it 335 * assume that the drop rate that controlled the queue on the 336 * last cycle is a good starting point to control it now. 337 */ 338 delta = vars->count - vars->lastcount; 339 if (delta > 1 && 340 codel_time_before(now - vars->drop_next, 341 16 * params->interval)) { 342 vars->count = delta; 343 /* we dont care if rec_inv_sqrt approximation 344 * is not very precise : 345 * Next Newton steps will correct it quadratically. 346 */ 347 codel_Newton_step(vars); 348 } else { 349 vars->count = 1; 350 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; 351 } 352 vars->lastcount = vars->count; 353 vars->drop_next = codel_control_law(now, params->interval, 354 vars->rec_inv_sqrt); 355 } 356 end: 357 return skb; 358 } 359 #endif 360