projects/linux·blob v3.13 · refs

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1#ifndef __NET_SCHED_CODEL_H
2#define __NET_SCHED_CODEL_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 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#include <linux/types.h>
45#include <linux/ktime.h>
46#include <linux/skbuff.h>
47#include <net/pkt_sched.h>
48#include <net/inet_ecn.h>
49#include <linux/reciprocal_div.h>
50
51/* Controlling Queue Delay (CoDel) algorithm
52 * =========================================
53 * Source : Kathleen Nichols and Van Jacobson
54 * http://queue.acm.org/detail.cfm?id=2209336
55 *
56 * Implemented on linux by Dave Taht and Eric Dumazet
57 */
58
59
60/* CoDel uses a 1024 nsec clock, encoded in u32
61 * This gives a range of 2199 seconds, because of signed compares
62 */
63typedef u32 codel_time_t;
64typedef s32 codel_tdiff_t;
65#define CODEL_SHIFT 10
66#define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)
67
68static inline codel_time_t codel_get_time(void)
69{
70 u64 ns = ktime_to_ns(ktime_get());
71
72 return ns >> CODEL_SHIFT;
73}
74
75/* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia:
76 * https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
77 * codel_time_after(a,b) returns true if the time a is after time b.
78 */
79#define codel_time_after(a, b) \
80 (typecheck(codel_time_t, a) && \
81 typecheck(codel_time_t, b) && \
82 ((s32)((a) - (b)) > 0))
83#define codel_time_before(a, b) codel_time_after(b, a)
84
85#define codel_time_after_eq(a, b) \
86 (typecheck(codel_time_t, a) && \
87 typecheck(codel_time_t, b) && \
88 ((s32)((a) - (b)) >= 0))
89#define codel_time_before_eq(a, b) codel_time_after_eq(b, a)
90
91/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
92struct codel_skb_cb {
93 codel_time_t enqueue_time;
94};
95
96static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
97{
98 qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
99 return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
100}
101
102static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
103{
104 return get_codel_cb(skb)->enqueue_time;
105}
106
107static void codel_set_enqueue_time(struct sk_buff *skb)
108{
109 get_codel_cb(skb)->enqueue_time = codel_get_time();
110}
111
112static inline u32 codel_time_to_us(codel_time_t val)
113{
114 u64 valns = ((u64)val << CODEL_SHIFT);
115
116 do_div(valns, NSEC_PER_USEC);
117 return (u32)valns;
118}
119
120/**
121 * struct codel_params - contains codel parameters
122 * @target: target queue size (in time units)
123 * @interval: width of moving time window
124 * @ecn: is Explicit Congestion Notification enabled
125 */
126struct codel_params {
127 codel_time_t target;
128 codel_time_t interval;
129 bool ecn;
130};
131
132/**
133 * struct codel_vars - contains codel variables
134 * @count: how many drops we've done since the last time we
135 * entered dropping state
136 * @lastcount: count at entry to dropping state
137 * @dropping: set to true if in dropping state
138 * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
139 * @first_above_time: when we went (or will go) continuously above target
140 * for interval
141 * @drop_next: time to drop next packet, or when we dropped last
142 * @ldelay: sojourn time of last dequeued packet
143 */
144struct codel_vars {
145 u32 count;
146 u32 lastcount;
147 bool dropping;
148 u16 rec_inv_sqrt;
149 codel_time_t first_above_time;
150 codel_time_t drop_next;
151 codel_time_t ldelay;
152};
153
154#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
155/* needed shift to get a Q0.32 number from rec_inv_sqrt */
156#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
157
158/**
159 * struct codel_stats - contains codel shared variables and stats
160 * @maxpacket: largest packet we've seen so far
161 * @drop_count: temp count of dropped packets in dequeue()
162 * ecn_mark: number of packets we ECN marked instead of dropping
163 */
164struct codel_stats {
165 u32 maxpacket;
166 u32 drop_count;
167 u32 ecn_mark;
168};
169
170static void codel_params_init(struct codel_params *params)
171{
172 params->interval = MS2TIME(100);
173 params->target = MS2TIME(5);
174 params->ecn = false;
175}
176
177static void codel_vars_init(struct codel_vars *vars)
178{
179 memset(vars, 0, sizeof(*vars));
180}
181
182static void codel_stats_init(struct codel_stats *stats)
183{
184 stats->maxpacket = 256;
185}
186
187/*
188 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
189 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
190 *
191 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
192 */
193static void codel_Newton_step(struct codel_vars *vars)
194{
195 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
196 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
197 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
198
199 val >>= 2; /* avoid overflow in following multiply */
200 val = (val * invsqrt) >> (32 - 2 + 1);
201
202 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
203}
204
205/*
206 * CoDel control_law is t + interval/sqrt(count)
207 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
208 * both sqrt() and divide operation.
209 */
210static codel_time_t codel_control_law(codel_time_t t,
211 codel_time_t interval,
212 u32 rec_inv_sqrt)
213{
214 return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
215}
216
217
218static bool codel_should_drop(const struct sk_buff *skb,
219 struct Qdisc *sch,
220 struct codel_vars *vars,
221 struct codel_params *params,
222 struct codel_stats *stats,
223 codel_time_t now)
224{
225 bool ok_to_drop;
226
227 if (!skb) {
228 vars->first_above_time = 0;
229 return false;
230 }
231
232 vars->ldelay = now - codel_get_enqueue_time(skb);
233 sch->qstats.backlog -= qdisc_pkt_len(skb);
234
235 if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
236 stats->maxpacket = qdisc_pkt_len(skb);
237
238 if (codel_time_before(vars->ldelay, params->target) ||
239 sch->qstats.backlog <= stats->maxpacket) {
240 /* went below - stay below for at least interval */
241 vars->first_above_time = 0;
242 return false;
243 }
244 ok_to_drop = false;
245 if (vars->first_above_time == 0) {
246 /* just went above from below. If we stay above
247 * for at least interval we'll say it's ok to drop
248 */
249 vars->first_above_time = now + params->interval;
250 } else if (codel_time_after(now, vars->first_above_time)) {
251 ok_to_drop = true;
252 }
253 return ok_to_drop;
254}
255
256typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
257 struct Qdisc *sch);
258
259static struct sk_buff *codel_dequeue(struct Qdisc *sch,
260 struct codel_params *params,
261 struct codel_vars *vars,
262 struct codel_stats *stats,
263 codel_skb_dequeue_t dequeue_func)
264{
265 struct sk_buff *skb = dequeue_func(vars, sch);
266 codel_time_t now;
267 bool drop;
268
269 if (!skb) {
270 vars->dropping = false;
271 return skb;
272 }
273 now = codel_get_time();
274 drop = codel_should_drop(skb, sch, vars, params, stats, now);
275 if (vars->dropping) {
276 if (!drop) {
277 /* sojourn time below target - leave dropping state */
278 vars->dropping = false;
279 } else if (codel_time_after_eq(now, vars->drop_next)) {
280 /* It's time for the next drop. Drop the current
281 * packet and dequeue the next. The dequeue might
282 * take us out of dropping state.
283 * If not, schedule the next drop.
284 * A large backlog might result in drop rates so high
285 * that the next drop should happen now,
286 * hence the while loop.
287 */
288 while (vars->dropping &&
289 codel_time_after_eq(now, vars->drop_next)) {
290 vars->count++; /* dont care of possible wrap
291 * since there is no more divide
292 */
293 codel_Newton_step(vars);
294 if (params->ecn && INET_ECN_set_ce(skb)) {
295 stats->ecn_mark++;
296 vars->drop_next =
297 codel_control_law(vars->drop_next,
298 params->interval,
299 vars->rec_inv_sqrt);
300 goto end;
301 }
302 qdisc_drop(skb, sch);
303 stats->drop_count++;
304 skb = dequeue_func(vars, sch);
305 if (!codel_should_drop(skb, sch,
306 vars, params, stats, now)) {
307 /* leave dropping state */
308 vars->dropping = false;
309 } else {
310 /* and schedule the next drop */
311 vars->drop_next =
312 codel_control_law(vars->drop_next,
313 params->interval,
314 vars->rec_inv_sqrt);
315 }
316 }
317 }
318 } else if (drop) {
319 u32 delta;
320
321 if (params->ecn && INET_ECN_set_ce(skb)) {
322 stats->ecn_mark++;
323 } else {
324 qdisc_drop(skb, sch);
325 stats->drop_count++;
326
327 skb = dequeue_func(vars, sch);
328 drop = codel_should_drop(skb, sch, vars, params,
329 stats, now);
330 }
331 vars->dropping = true;
332 /* if min went above target close to when we last went below it
333 * assume that the drop rate that controlled the queue on the
334 * last cycle is a good starting point to control it now.
335 */
336 delta = vars->count - vars->lastcount;
337 if (delta > 1 &&
338 codel_time_before(now - vars->drop_next,
339 16 * params->interval)) {
340 vars->count = delta;
341 /* we dont care if rec_inv_sqrt approximation
342 * is not very precise :
343 * Next Newton steps will correct it quadratically.
344 */
345 codel_Newton_step(vars);
346 } else {
347 vars->count = 1;
348 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
349 }
350 vars->lastcount = vars->count;
351 vars->drop_next = codel_control_law(now, params->interval,
352 vars->rec_inv_sqrt);
353 }
354end:
355 return skb;
356}
357#endif