1 /* 2 * Codel - The Controlled-Delay Active Queue Management algorithm. 3 * 4 * $FreeBSD$ 5 * 6 * Copyright (C) 2016 Centre for Advanced Internet Architectures, 7 * Swinburne University of Technology, Melbourne, Australia. 8 * Portions of this code were made possible in part by a gift from 9 * The Comcast Innovation Fund. 10 * Implemented by Rasool Al-Saadi <ralsaadi@swin.edu.au> 11 * 12 * Copyright (C) 2011-2014 Kathleen Nichols <nichols@pollere.com>. 13 * 14 * Redistribution and use in source and binary forms, with or without 15 * modification, are permitted provided that the following conditions 16 * are met: 17 * 18 * o Redistributions of source code must retain the above copyright 19 * notice, this list of conditions, and the following disclaimer, 20 * without modification. 21 * 22 * o Redistributions in binary form must reproduce the above copyright 23 * notice, this list of conditions and the following disclaimer in 24 * the documentation and/or other materials provided with the 25 * distribution. 26 * 27 * o The names of the authors may not be used to endorse or promote 28 * products derived from this software without specific prior written 29 * permission. 30 * 31 * Alternatively, provided that this notice is retained in full, this 32 * software may be distributed under the terms of the GNU General Public 33 * License ("GPL") version 2, in which case the provisions of the GPL 34 * apply INSTEAD OF those given above. 35 36 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 37 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 38 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 39 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 40 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 41 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 42 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 43 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 44 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 45 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 46 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 47 */ 48 49 #ifndef _IP_DN_AQM_CODEL_H 50 #define _IP_DN_AQM_CODEL_H 51 52 // XXX How to choose MTAG? 53 #define FIX_POINT_BITS 16 54 55 enum { 56 CODEL_ECN_ENABLED = 1 57 }; 58 59 /* Codel parameters */ 60 struct dn_aqm_codel_parms { 61 aqm_time_t target; 62 aqm_time_t interval; 63 uint32_t flags; 64 }; 65 66 /* codel status variables */ 67 struct codel_status { 68 uint32_t count; /* number of dropped pkts since entering drop state */ 69 uint16_t dropping; /* dropping state */ 70 aqm_time_t drop_next_time; /* time for next drop */ 71 aqm_time_t first_above_time; /* time for first ts over target we observed */ 72 uint16_t isqrt; /* last isqrt for control low */ 73 uint16_t maxpkt_size; /* max packet size seen so far */ 74 }; 75 76 struct mbuf *codel_extract_head(struct dn_queue *, aqm_time_t *); 77 aqm_time_t control_law(struct codel_status *, 78 struct dn_aqm_codel_parms *, aqm_time_t ); 79 80 __inline static struct mbuf * 81 codel_dodequeue(struct dn_queue *q, aqm_time_t now, uint16_t *ok_to_drop) 82 { 83 struct mbuf * m; 84 struct dn_aqm_codel_parms *cprms; 85 struct codel_status *cst; 86 aqm_time_t pkt_ts, sojourn_time; 87 88 *ok_to_drop = 0; 89 m = codel_extract_head(q, &pkt_ts); 90 91 cst = q->aqm_status; 92 93 if (m == NULL) { 94 /* queue is empty - we can't be above target */ 95 cst->first_above_time= 0; 96 return m; 97 } 98 99 cprms = q->fs->aqmcfg; 100 101 /* To span a large range of bandwidths, CoDel runs two 102 * different AQMs in parallel. One is sojourn-time-based 103 * and takes effect when the time to send an MTU-sized 104 * packet is less than target. The 1st term of the "if" 105 * below does this. The other is backlog-based and takes 106 * effect when the time to send an MTU-sized packet is >= 107 * target. The goal here is to keep the output link 108 * utilization high by never allowing the queue to get 109 * smaller than the amount that arrives in a typical 110 * interarrival time (MTU-sized packets arriving spaced 111 * by the amount of time it takes to send such a packet on 112 * the bottleneck). The 2nd term of the "if" does this. 113 */ 114 sojourn_time = now - pkt_ts; 115 if (sojourn_time < cprms->target || q->ni.len_bytes <= cst->maxpkt_size) { 116 /* went below - stay below for at least interval */ 117 cst->first_above_time = 0; 118 } else { 119 if (cst->first_above_time == 0) { 120 /* just went above from below. if still above at 121 * first_above_time, will say it's ok to drop. */ 122 cst->first_above_time = now + cprms->interval; 123 } else if (now >= cst->first_above_time) { 124 *ok_to_drop = 1; 125 } 126 } 127 return m; 128 } 129 130 /* 131 * Dequeue a packet from queue 'q' 132 */ 133 __inline static struct mbuf * 134 codel_dequeue(struct dn_queue *q) 135 { 136 struct mbuf *m; 137 struct dn_aqm_codel_parms *cprms; 138 struct codel_status *cst; 139 aqm_time_t now; 140 uint16_t ok_to_drop; 141 142 cst = q->aqm_status;; 143 cprms = q->fs->aqmcfg; 144 now = AQM_UNOW; 145 146 m = codel_dodequeue(q, now, &ok_to_drop); 147 if (cst->dropping) { 148 if (!ok_to_drop) { 149 /* sojourn time below target - leave dropping state */ 150 cst->dropping = false; 151 } 152 /* 153 * Time for the next drop. Drop current packet and dequeue 154 * next. If the dequeue doesn't take us out of dropping 155 * state, schedule the next drop. A large backlog might 156 * result in drop rates so high that the next drop should 157 * happen now, hence the 'while' loop. 158 */ 159 while (now >= cst->drop_next_time && cst->dropping) { 160 /* mark the packet */ 161 if (cprms->flags & CODEL_ECN_ENABLED && ecn_mark(m)) { 162 cst->count++; 163 /* schedule the next mark. */ 164 cst->drop_next_time = control_law(cst, cprms, 165 cst->drop_next_time); 166 return m; 167 } 168 169 /* drop the packet */ 170 update_stats(q, 0, 1); 171 FREE_PKT(m); 172 m = codel_dodequeue(q, now, &ok_to_drop); 173 174 if (!ok_to_drop) { 175 /* leave dropping state */ 176 cst->dropping = false; 177 } else { 178 cst->count++; 179 /* schedule the next drop. */ 180 cst->drop_next_time = control_law(cst, cprms, 181 cst->drop_next_time); 182 } 183 } 184 /* If we get here we're not in dropping state. The 'ok_to_drop' 185 * return from dodequeue means that the sojourn time has been 186 * above 'target' for 'interval' so enter dropping state. 187 */ 188 } else if (ok_to_drop) { 189 /* if ECN option is disabled or the packet cannot be marked, 190 * drop the packet and extract another. 191 */ 192 if (!(cprms->flags & CODEL_ECN_ENABLED) || !ecn_mark(m)) { 193 update_stats(q, 0, 1); 194 FREE_PKT(m); 195 m = codel_dodequeue(q, now, &ok_to_drop); 196 } 197 198 cst->dropping = true; 199 200 /* If min went above target close to when it last went 201 * below, assume that the drop rate that controlled the 202 * queue on the last cycle is a good starting point to 203 * control it now. ('drop_next' will be at most 'interval' 204 * later than the time of the last drop so 'now - drop_next' 205 * is a good approximation of the time from the last drop 206 * until now.) 207 */ 208 cst->count = (cst->count > 2 && ((aqm_stime_t)now - 209 (aqm_stime_t)cst->drop_next_time) < 8* cprms->interval)? 210 cst->count - 2 : 1; 211 /* we don't have to set initial guess for Newton's method isqrt as 212 * we initilaize isqrt in control_law function when count == 1 */ 213 cst->drop_next_time = control_law(cst, cprms, now); 214 } 215 216 return m; 217 } 218 219 #endif 220