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
52#include <net/inet_ecn.h>
53
54static void codel_params_init(struct codel_params *params)
55{
56 params->interval = MS2TIME(100);
57 params->target = MS2TIME(5);
58 params->ce_threshold = CODEL_DISABLED_THRESHOLD;
59 params->ce_threshold_mask = 0;
60 params->ce_threshold_selector = 0;
61 params->ecn = false;
62}
63
64static void codel_vars_init(struct codel_vars *vars)
65{
66 memset(s: vars, c: 0, n: sizeof(*vars));
67}
68
69static void codel_stats_init(struct codel_stats *stats)
70{
71 stats->maxpacket = 0;
72}
73
74/*
75 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
76 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
77 *
78 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
79 */
80static void codel_Newton_step(struct codel_vars *vars)
81{
82 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
83 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
84 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
85
86 val >>= 2; /* avoid overflow in following multiply */
87 val = (val * invsqrt) >> (32 - 2 + 1);
88
89 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
90}
91
92/*
93 * CoDel control_law is t + interval/sqrt(count)
94 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
95 * both sqrt() and divide operation.
96 */
97static codel_time_t codel_control_law(codel_time_t t,
98 codel_time_t interval,
99 u32 rec_inv_sqrt)
100{
101 return t + reciprocal_scale(val: interval, ep_ro: rec_inv_sqrt << REC_INV_SQRT_SHIFT);
102}
103
104static bool codel_should_drop(const struct sk_buff *skb,
105 void *ctx,
106 struct codel_vars *vars,
107 struct codel_params *params,
108 struct codel_stats *stats,
109 codel_skb_len_t skb_len_func,
110 codel_skb_time_t skb_time_func,
111 u32 *backlog,
112 codel_time_t now)
113{
114 bool ok_to_drop;
115 u32 skb_len;
116
117 if (!skb) {
118 vars->first_above_time = 0;
119 return false;
120 }
121
122 skb_len = skb_len_func(skb);
123 vars->ldelay = now - skb_time_func(skb);
124
125 if (unlikely(skb_len > stats->maxpacket))
126 stats->maxpacket = skb_len;
127
128 if (codel_time_before(vars->ldelay, params->target) ||
129 *backlog <= params->mtu) {
130 /* went below - stay below for at least interval */
131 vars->first_above_time = 0;
132 return false;
133 }
134 ok_to_drop = false;
135 if (vars->first_above_time == 0) {
136 /* just went above from below. If we stay above
137 * for at least interval we'll say it's ok to drop
138 */
139 vars->first_above_time = now + params->interval;
140 } else if (codel_time_after(now, vars->first_above_time)) {
141 ok_to_drop = true;
142 }
143 return ok_to_drop;
144}
145
146static struct sk_buff *codel_dequeue(void *ctx,
147 u32 *backlog,
148 struct codel_params *params,
149 struct codel_vars *vars,
150 struct codel_stats *stats,
151 codel_skb_len_t skb_len_func,
152 codel_skb_time_t skb_time_func,
153 codel_skb_drop_t drop_func,
154 codel_skb_dequeue_t dequeue_func)
155{
156 struct sk_buff *skb = dequeue_func(vars, ctx);
157 codel_time_t now;
158 bool drop;
159
160 if (!skb) {
161 vars->dropping = false;
162 return skb;
163 }
164 now = codel_get_time();
165 drop = codel_should_drop(skb, ctx, vars, params, stats,
166 skb_len_func, skb_time_func, backlog, now);
167 if (vars->dropping) {
168 if (!drop) {
169 /* sojourn time below target - leave dropping state */
170 vars->dropping = false;
171 } else if (codel_time_after_eq(now, vars->drop_next)) {
172 /* It's time for the next drop. Drop the current
173 * packet and dequeue the next. The dequeue might
174 * take us out of dropping state.
175 * If not, schedule the next drop.
176 * A large backlog might result in drop rates so high
177 * that the next drop should happen now,
178 * hence the while loop.
179 */
180 while (vars->dropping &&
181 codel_time_after_eq(now, vars->drop_next)) {
182 vars->count++; /* dont care of possible wrap
183 * since there is no more divide
184 */
185 codel_Newton_step(vars);
186 if (params->ecn && INET_ECN_set_ce(skb)) {
187 stats->ecn_mark++;
188 vars->drop_next =
189 codel_control_law(t: vars->drop_next,
190 interval: params->interval,
191 rec_inv_sqrt: vars->rec_inv_sqrt);
192 goto end;
193 }
194 stats->drop_len += skb_len_func(skb);
195 drop_func(skb, ctx);
196 stats->drop_count++;
197 skb = dequeue_func(vars, ctx);
198 if (!codel_should_drop(skb, ctx,
199 vars, params, stats,
200 skb_len_func,
201 skb_time_func,
202 backlog, now)) {
203 /* leave dropping state */
204 vars->dropping = false;
205 } else {
206 /* and schedule the next drop */
207 vars->drop_next =
208 codel_control_law(t: vars->drop_next,
209 interval: params->interval,
210 rec_inv_sqrt: vars->rec_inv_sqrt);
211 }
212 }
213 }
214 } else if (drop) {
215 u32 delta;
216
217 if (params->ecn && INET_ECN_set_ce(skb)) {
218 stats->ecn_mark++;
219 } else {
220 stats->drop_len += skb_len_func(skb);
221 drop_func(skb, ctx);
222 stats->drop_count++;
223
224 skb = dequeue_func(vars, ctx);
225 drop = codel_should_drop(skb, ctx, vars, params,
226 stats, skb_len_func,
227 skb_time_func, backlog, now);
228 }
229 vars->dropping = true;
230 /* if min went above target close to when we last went below it
231 * assume that the drop rate that controlled the queue on the
232 * last cycle is a good starting point to control it now.
233 */
234 delta = vars->count - vars->lastcount;
235 if (delta > 1 &&
236 codel_time_before(now - vars->drop_next,
237 16 * params->interval)) {
238 vars->count = delta;
239 /* we dont care if rec_inv_sqrt approximation
240 * is not very precise :
241 * Next Newton steps will correct it quadratically.
242 */
243 codel_Newton_step(vars);
244 } else {
245 vars->count = 1;
246 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
247 }
248 vars->lastcount = vars->count;
249 vars->drop_next = codel_control_law(t: now, interval: params->interval,
250 rec_inv_sqrt: vars->rec_inv_sqrt);
251 }
252end:
253 if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
254 bool set_ce = true;
255
256 if (params->ce_threshold_mask) {
257 int dsfield = skb_get_dsfield(skb);
258
259 set_ce = (dsfield >= 0 &&
260 (((u8)dsfield & params->ce_threshold_mask) ==
261 params->ce_threshold_selector));
262 }
263 if (set_ce && INET_ECN_set_ce(skb))
264 stats->ce_mark++;
265 }
266 return skb;
267}
268
269#endif
270