1#ifndef __NET_SCHED_CODEL_IMPL_H
2#define __NET_SCHED_CODEL_IMPL_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/* Controlling Queue Delay (CoDel) algorithm
45 * =========================================
46 * Source : Kathleen Nichols and Van Jacobson
47 * http://queue.acm.org/detail.cfm?id=2209336
48 *
49 * Implemented on linux by Dave Taht and Eric Dumazet
50 */
51
52static void codel_params_init(struct codel_params *params)
53{
54 params->interval = MS2TIME(100);
55 params->target = MS2TIME(5);
56 params->ce_threshold = CODEL_DISABLED_THRESHOLD;
57 params->ecn = false;
58}
59
60static void codel_vars_init(struct codel_vars *vars)
61{
62 memset(vars, 0, sizeof(*vars));
63}
64
65static void codel_stats_init(struct codel_stats *stats)
66{
67 stats->maxpacket = 0;
68}
69
70/*
71 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
72 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
73 *
74 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
75 */
76static void codel_Newton_step(struct codel_vars *vars)
77{
78 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
79 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
80 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
81
82 val >>= 2; /* avoid overflow in following multiply */
83 val = (val * invsqrt) >> (32 - 2 + 1);
84
85 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
86}
87
88/*
89 * CoDel control_law is t + interval/sqrt(count)
90 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
91 * both sqrt() and divide operation.
92 */
93static codel_time_t codel_control_law(codel_time_t t,
94 codel_time_t interval,
95 u32 rec_inv_sqrt)
96{
97 return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
98}
99
100static bool codel_should_drop(const struct sk_buff *skb,
101 void *ctx,
102 struct codel_vars *vars,
103 struct codel_params *params,
104 struct codel_stats *stats,
105 codel_skb_len_t skb_len_func,
106 codel_skb_time_t skb_time_func,
107 u32 *backlog,
108 codel_time_t now)
109{
110 bool ok_to_drop;
111 u32 skb_len;
112
113 if (!skb) {
114 vars->first_above_time = 0;
115 return false;
116 }
117
118 skb_len = skb_len_func(skb);
119 vars->ldelay = now - skb_time_func(skb);
120
121 if (unlikely(skb_len > stats->maxpacket))
122 stats->maxpacket = skb_len;
123
124 if (codel_time_before(vars->ldelay, params->target) ||
125 *backlog <= params->mtu) {
126 /* went below - stay below for at least interval */
127 vars->first_above_time = 0;
128 return false;
129 }
130 ok_to_drop = false;
131 if (vars->first_above_time == 0) {
132 /* just went above from below. If we stay above
133 * for at least interval we'll say it's ok to drop
134 */
135 vars->first_above_time = now + params->interval;
136 } else if (codel_time_after(now, vars->first_above_time)) {
137 ok_to_drop = true;
138 }
139 return ok_to_drop;
140}
141
142static struct sk_buff *codel_dequeue(void *ctx,
143 u32 *backlog,
144 struct codel_params *params,
145 struct codel_vars *vars,
146 struct codel_stats *stats,
147 codel_skb_len_t skb_len_func,
148 codel_skb_time_t skb_time_func,
149 codel_skb_drop_t drop_func,
150 codel_skb_dequeue_t dequeue_func)
151{
152 struct sk_buff *skb = dequeue_func(vars, ctx);
153 codel_time_t now;
154 bool drop;
155
156 if (!skb) {
157 vars->dropping = false;
158 return skb;
159 }
160 now = codel_get_time();
161 drop = codel_should_drop(skb, ctx, vars, params, stats,
162 skb_len_func, skb_time_func, backlog, now);
163 if (vars->dropping) {
164 if (!drop) {
165 /* sojourn time below target - leave dropping state */
166 vars->dropping = false;
167 } else if (codel_time_after_eq(now, vars->drop_next)) {
168 /* It's time for the next drop. Drop the current
169 * packet and dequeue the next. The dequeue might
170 * take us out of dropping state.
171 * If not, schedule the next drop.
172 * A large backlog might result in drop rates so high
173 * that the next drop should happen now,
174 * hence the while loop.
175 */
176 while (vars->dropping &&
177 codel_time_after_eq(now, vars->drop_next)) {
178 vars->count++; /* dont care of possible wrap
179 * since there is no more divide
180 */
181 codel_Newton_step(vars);
182 if (params->ecn && INET_ECN_set_ce(skb)) {
183 stats->ecn_mark++;
184 vars->drop_next =
185 codel_control_law(vars->drop_next,
186 params->interval,
187 vars->rec_inv_sqrt);
188 goto end;
189 }
190 stats->drop_len += skb_len_func(skb);
191 drop_func(skb, ctx);
192 stats->drop_count++;
193 skb = dequeue_func(vars, ctx);
194 if (!codel_should_drop(skb, ctx,
195 vars, params, stats,
196 skb_len_func,
197 skb_time_func,
198 backlog, now)) {
199 /* leave dropping state */
200 vars->dropping = false;
201 } else {
202 /* and schedule the next drop */
203 vars->drop_next =
204 codel_control_law(vars->drop_next,
205 params->interval,
206 vars->rec_inv_sqrt);
207 }
208 }
209 }
210 } else if (drop) {
211 u32 delta;
212
213 if (params->ecn && INET_ECN_set_ce(skb)) {
214 stats->ecn_mark++;
215 } else {
216 stats->drop_len += skb_len_func(skb);
217 drop_func(skb, ctx);
218 stats->drop_count++;
219
220 skb = dequeue_func(vars, ctx);
221 drop = codel_should_drop(skb, ctx, vars, params,
222 stats, skb_len_func,
223 skb_time_func, backlog, now);
224 }
225 vars->dropping = true;
226 /* if min went above target close to when we last went below it
227 * assume that the drop rate that controlled the queue on the
228 * last cycle is a good starting point to control it now.
229 */
230 delta = vars->count - vars->lastcount;
231 if (delta > 1 &&
232 codel_time_before(now - vars->drop_next,
233 16 * params->interval)) {
234 vars->count = delta;
235 /* we dont care if rec_inv_sqrt approximation
236 * is not very precise :
237 * Next Newton steps will correct it quadratically.
238 */
239 codel_Newton_step(vars);
240 } else {
241 vars->count = 1;
242 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
243 }
244 vars->lastcount = vars->count;
245 vars->drop_next = codel_control_law(now, params->interval,
246 vars->rec_inv_sqrt);
247 }
248end:
249 if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
250 INET_ECN_set_ce(skb))
251 stats->ce_mark++;
252 return skb;
253}
254
255#endif
256