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