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