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
codel_params_init(struct codel_params * params)54 static 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
codel_vars_init(struct codel_vars * vars)64 static void codel_vars_init(struct codel_vars *vars)
65 {
66 memset(vars, 0, sizeof(*vars));
67 }
68
codel_stats_init(struct codel_stats * stats)69 static 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 */
codel_Newton_step(struct codel_vars * vars)80 static 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 */
codel_control_law(codel_time_t t,codel_time_t interval,u32 rec_inv_sqrt)97 static 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(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
102 }
103
codel_should_drop(const struct sk_buff * skb,void * ctx,struct codel_vars * vars,struct codel_params * params,struct codel_stats * stats,codel_skb_len_t skb_len_func,codel_skb_time_t skb_time_func,u32 * backlog,codel_time_t now)104 static 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
codel_dequeue(void * ctx,u32 * backlog,struct codel_params * params,struct codel_vars * vars,struct codel_stats * stats,codel_skb_len_t skb_len_func,codel_skb_time_t skb_time_func,codel_skb_drop_t drop_func,codel_skb_dequeue_t dequeue_func)146 static 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->first_above_time = 0;
162 vars->dropping = false;
163 return skb;
164 }
165 now = codel_get_time();
166 drop = codel_should_drop(skb, ctx, vars, params, stats,
167 skb_len_func, skb_time_func, backlog, now);
168 if (vars->dropping) {
169 if (!drop) {
170 /* sojourn time below target - leave dropping state */
171 vars->dropping = false;
172 } else if (codel_time_after_eq(now, vars->drop_next)) {
173 /* It's time for the next drop. Drop the current
174 * packet and dequeue the next. The dequeue might
175 * take us out of dropping state.
176 * If not, schedule the next drop.
177 * A large backlog might result in drop rates so high
178 * that the next drop should happen now,
179 * hence the while loop.
180 */
181 while (vars->dropping &&
182 codel_time_after_eq(now, vars->drop_next)) {
183 vars->count++; /* dont care of possible wrap
184 * since there is no more divide
185 */
186 codel_Newton_step(vars);
187 if (params->ecn && INET_ECN_set_ce(skb)) {
188 stats->ecn_mark++;
189 vars->drop_next =
190 codel_control_law(vars->drop_next,
191 params->interval,
192 vars->rec_inv_sqrt);
193 goto end;
194 }
195 stats->drop_len += skb_len_func(skb);
196 drop_func(skb, ctx);
197 stats->drop_count++;
198 skb = dequeue_func(vars, ctx);
199 if (!codel_should_drop(skb, ctx,
200 vars, params, stats,
201 skb_len_func,
202 skb_time_func,
203 backlog, now)) {
204 /* leave dropping state */
205 vars->dropping = false;
206 } else {
207 /* and schedule the next drop */
208 vars->drop_next =
209 codel_control_law(vars->drop_next,
210 params->interval,
211 vars->rec_inv_sqrt);
212 }
213 }
214 }
215 } else if (drop) {
216 u32 delta;
217
218 if (params->ecn && INET_ECN_set_ce(skb)) {
219 stats->ecn_mark++;
220 } else {
221 stats->drop_len += skb_len_func(skb);
222 drop_func(skb, ctx);
223 stats->drop_count++;
224
225 skb = dequeue_func(vars, ctx);
226 drop = codel_should_drop(skb, ctx, vars, params,
227 stats, skb_len_func,
228 skb_time_func, backlog, now);
229 }
230 vars->dropping = true;
231 /* if min went above target close to when we last went below it
232 * assume that the drop rate that controlled the queue on the
233 * last cycle is a good starting point to control it now.
234 */
235 delta = vars->count - vars->lastcount;
236 if (delta > 1 &&
237 codel_time_before(now - vars->drop_next,
238 16 * params->interval)) {
239 vars->count = delta;
240 /* we dont care if rec_inv_sqrt approximation
241 * is not very precise :
242 * Next Newton steps will correct it quadratically.
243 */
244 codel_Newton_step(vars);
245 } else {
246 vars->count = 1;
247 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
248 }
249 vars->lastcount = vars->count;
250 vars->drop_next = codel_control_law(now, params->interval,
251 vars->rec_inv_sqrt);
252 }
253 end:
254 if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
255 bool set_ce = true;
256
257 if (params->ce_threshold_mask) {
258 int dsfield = skb_get_dsfield(skb);
259
260 set_ce = (dsfield >= 0 &&
261 (((u8)dsfield & params->ce_threshold_mask) ==
262 params->ce_threshold_selector));
263 }
264 if (set_ce && INET_ECN_set_ce(skb))
265 stats->ce_mark++;
266 }
267 return skb;
268 }
269
270 #endif
271