projects/linux·blob uaccess-cleanups · refs

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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 <[email protected]>
8 * Copyright (C) 2011-2012 Van Jacobson <[email protected]>
9 * Copyright (C) 2012 Michael D. Taht <[email protected]>
10 * Copyright (C) 2012,2015 Eric Dumazet <[email protected]>
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(vars, 0, 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 *
97 * Clamp the increment to at least 1 tick: a very small interval (or a
98 * large count) can truncate it to zero, stalling the dropping loop.
99 */
100static codel_time_t codel_control_law(codel_time_t t,
101 codel_time_t interval,
102 u32 rec_inv_sqrt)
103{
104 return t + max_t(u32, 1,
105 reciprocal_scale(interval,
106 rec_inv_sqrt << REC_INV_SQRT_SHIFT));
107}
108
109static bool codel_should_drop(const struct sk_buff *skb,
110 void *ctx,
111 struct codel_vars *vars,
112 struct codel_params *params,
113 struct codel_stats *stats,
114 codel_skb_len_t skb_len_func,
115 codel_skb_time_t skb_time_func,
116 u32 *backlog,
117 codel_time_t now)
118{
119 bool ok_to_drop;
120 u32 skb_len;
121
122 if (!skb) {
123 vars->first_above_time = 0;
124 return false;
125 }
126
127 skb_len = skb_len_func(skb);
128 WRITE_ONCE(vars->ldelay, now - skb_time_func(skb));
129
130 if (unlikely(skb_len > stats->maxpacket))
131 WRITE_ONCE(stats->maxpacket, skb_len);
132
133 if (codel_time_before(vars->ldelay, params->target) ||
134 *backlog <= params->mtu) {
135 /* went below - stay below for at least interval */
136 vars->first_above_time = 0;
137 return false;
138 }
139 ok_to_drop = false;
140 if (vars->first_above_time == 0) {
141 /* just went above from below. If we stay above
142 * for at least interval we'll say it's ok to drop
143 */
144 vars->first_above_time = now + params->interval;
145 } else if (codel_time_after(now, vars->first_above_time)) {
146 ok_to_drop = true;
147 }
148 return ok_to_drop;
149}
150
151static struct sk_buff *codel_dequeue(void *ctx,
152 u32 *backlog,
153 struct codel_params *params,
154 struct codel_vars *vars,
155 struct codel_stats *stats,
156 codel_skb_len_t skb_len_func,
157 codel_skb_time_t skb_time_func,
158 codel_skb_drop_t drop_func,
159 codel_skb_dequeue_t dequeue_func)
160{
161 struct sk_buff *skb = dequeue_func(vars, ctx);
162 unsigned int drops = 0;
163 codel_time_t now;
164 bool drop;
165
166 if (!skb) {
167 vars->first_above_time = 0;
168 WRITE_ONCE(vars->dropping, false);
169 return skb;
170 }
171 now = codel_get_time();
172 drop = codel_should_drop(skb, ctx, vars, params, stats,
173 skb_len_func, skb_time_func, backlog, now);
174 if (vars->dropping) {
175 if (!drop) {
176 /* sojourn time below target - leave dropping state */
177 WRITE_ONCE(vars->dropping, false);
178 } else if (codel_time_after_eq(now, vars->drop_next)) {
179 /* It's time for the next drop. Drop the current
180 * packet and dequeue the next. The dequeue might
181 * take us out of dropping state.
182 * If not, schedule the next drop.
183 * A large backlog might result in drop rates so high
184 * that the next drop should happen now,
185 * hence the while loop.
186 */
187 while (vars->dropping &&
188 codel_time_after_eq(now, vars->drop_next)) {
189 if (++drops > CODEL_MAX_DROPS_PER_DEQUEUE) {
190 /* fell far behind the schedule */
191 WRITE_ONCE(vars->drop_next,
192 codel_control_law(now,
193 params->interval,
194 vars->rec_inv_sqrt));
195 break;
196 }
197 /* dont care of possible wrap
198 * since there is no more divide.
199 */
200 WRITE_ONCE(vars->count, vars->count + 1);
201 codel_Newton_step(vars);
202 if (params->ecn && INET_ECN_set_ce(skb)) {
203 WRITE_ONCE(stats->ecn_mark,
204 stats->ecn_mark + 1);
205 WRITE_ONCE(vars->drop_next,
206 codel_control_law(vars->drop_next,
207 params->interval,
208 vars->rec_inv_sqrt));
209 goto end;
210 }
211 stats->drop_len += skb_len_func(skb);
212 drop_func(skb, ctx);
213 stats->drop_count++;
214 skb = dequeue_func(vars, ctx);
215 if (!codel_should_drop(skb, ctx,
216 vars, params, stats,
217 skb_len_func,
218 skb_time_func,
219 backlog, now)) {
220 /* leave dropping state */
221 WRITE_ONCE(vars->dropping, false);
222 } else {
223 /* and schedule the next drop */
224 WRITE_ONCE(vars->drop_next,
225 codel_control_law(vars->drop_next,
226 params->interval,
227 vars->rec_inv_sqrt));
228 }
229 }
230 }
231 } else if (drop) {
232 u32 delta;
233
234 if (params->ecn && INET_ECN_set_ce(skb)) {
235 WRITE_ONCE(stats->ecn_mark, stats->ecn_mark + 1);
236 } else {
237 stats->drop_len += skb_len_func(skb);
238 drop_func(skb, ctx);
239 stats->drop_count++;
240
241 skb = dequeue_func(vars, ctx);
242 drop = codel_should_drop(skb, ctx, vars, params,
243 stats, skb_len_func,
244 skb_time_func, backlog, now);
245 }
246 WRITE_ONCE(vars->dropping, true);
247 /* if min went above target close to when we last went below it
248 * assume that the drop rate that controlled the queue on the
249 * last cycle is a good starting point to control it now.
250 */
251 delta = vars->count - vars->lastcount;
252 if (delta > 1 &&
253 codel_time_before(now - vars->drop_next,
254 16 * params->interval)) {
255 WRITE_ONCE(vars->count, delta);
256 /* we dont care if rec_inv_sqrt approximation
257 * is not very precise :
258 * Next Newton steps will correct it quadratically.
259 */
260 codel_Newton_step(vars);
261 } else {
262 WRITE_ONCE(vars->count, 1);
263 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
264 }
265 WRITE_ONCE(vars->lastcount, vars->count);
266 WRITE_ONCE(vars->drop_next,
267 codel_control_law(now, params->interval,
268 vars->rec_inv_sqrt));
269 }
270end:
271 if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
272 bool set_ce = true;
273
274 if (params->ce_threshold_mask) {
275 int dsfield = skb_get_dsfield(skb);
276
277 set_ce = (dsfield >= 0 &&
278 (((u8)dsfield & params->ce_threshold_mask) ==
279 params->ce_threshold_selector));
280 }
281 if (set_ce && INET_ECN_set_ce(skb))
282 WRITE_ONCE(stats->ce_mark, stats->ce_mark + 1);
283 }
284 return skb;
285}
286
287#endif