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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 <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  */
63 typedef u32 codel_time_t;
64 typedef s32 codel_tdiff_t;
65 #define CODEL_SHIFT 10
66 #define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)
67
68 static 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[] */
92 struct codel_skb_cb {
93         codel_time_t enqueue_time;
94 };
95
96 static 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
102 static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
103 {
104         return get_codel_cb(skb)->enqueue_time;
105 }
106
107 static void codel_set_enqueue_time(struct sk_buff *skb)
108 {
109         get_codel_cb(skb)->enqueue_time = codel_get_time();
110 }
111
112 static 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  */
126 struct 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  */
144 struct 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  */
164 struct codel_stats {
165         u32             maxpacket;
166         u32             drop_count;
167         u32             ecn_mark;
168 };
169
170 static 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
177 static void codel_vars_init(struct codel_vars *vars)
178 {
179         memset(vars, 0, sizeof(*vars));
180 }
181
182 static 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  */
193 static 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  */
210 static 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
218 static 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
256 typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
257                                                 struct Qdisc *sch);
258
259 static 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         }
354 end:
355         return skb;
356 }
357 #endif