1 #ifndef __NET_SCHED_CODEL_H
2 #define __NET_SCHED_CODEL_H
5 * Codel - The Controlled-Delay Active Queue Management algorithm
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>
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
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.
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.
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
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>
50 /* Controlling Queue Delay (CoDel) algorithm
51 * =========================================
52 * Source : Kathleen Nichols and Van Jacobson
53 * http://queue.acm.org/detail.cfm?id=2209336
55 * Implemented on linux by Dave Taht and Eric Dumazet
59 /* CoDel uses a 1024 nsec clock, encoded in u32
60 * This gives a range of 2199 seconds, because of signed compares
62 typedef u32 codel_time_t
;
63 typedef s32 codel_tdiff_t
;
64 #define CODEL_SHIFT 10
65 #define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)
67 static inline codel_time_t
codel_get_time(void)
69 u64 ns
= ktime_get_ns();
71 return ns
>> CODEL_SHIFT
;
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.
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)
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)
90 /* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
92 codel_time_t enqueue_time
;
95 static struct codel_skb_cb
*get_codel_cb(const struct sk_buff
*skb
)
97 qdisc_cb_private_validate(skb
, sizeof(struct codel_skb_cb
));
98 return (struct codel_skb_cb
*)qdisc_skb_cb(skb
)->data
;
101 static codel_time_t
codel_get_enqueue_time(const struct sk_buff
*skb
)
103 return get_codel_cb(skb
)->enqueue_time
;
106 static void codel_set_enqueue_time(struct sk_buff
*skb
)
108 get_codel_cb(skb
)->enqueue_time
= codel_get_time();
111 static inline u32
codel_time_to_us(codel_time_t val
)
113 u64 valns
= ((u64
)val
<< CODEL_SHIFT
);
115 do_div(valns
, NSEC_PER_USEC
);
120 * struct codel_params - contains codel parameters
121 * @target: target queue size (in time units)
122 * @ce_threshold: threshold for marking packets with ECN CE
123 * @interval: width of moving time window
124 * @mtu: device mtu, or minimal queue backlog in bytes.
125 * @ecn: is Explicit Congestion Notification enabled
127 struct codel_params
{
129 codel_time_t ce_threshold
;
130 codel_time_t interval
;
136 * struct codel_vars - contains codel variables
137 * @count: how many drops we've done since the last time we
138 * entered dropping state
139 * @lastcount: count at entry to dropping state
140 * @dropping: set to true if in dropping state
141 * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
142 * @first_above_time: when we went (or will go) continuously above target
144 * @drop_next: time to drop next packet, or when we dropped last
145 * @ldelay: sojourn time of last dequeued packet
152 codel_time_t first_above_time
;
153 codel_time_t drop_next
;
157 #define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
158 /* needed shift to get a Q0.32 number from rec_inv_sqrt */
159 #define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
162 * struct codel_stats - contains codel shared variables and stats
163 * @maxpacket: largest packet we've seen so far
164 * @drop_count: temp count of dropped packets in dequeue()
165 * @drop_len: bytes of dropped packets in dequeue()
166 * ecn_mark: number of packets we ECN marked instead of dropping
167 * ce_mark: number of packets CE marked because sojourn time was above ce_threshold
177 #define CODEL_DISABLED_THRESHOLD INT_MAX
179 static void codel_params_init(struct codel_params
*params
)
181 params
->interval
= MS2TIME(100);
182 params
->target
= MS2TIME(5);
183 params
->ce_threshold
= CODEL_DISABLED_THRESHOLD
;
187 static void codel_vars_init(struct codel_vars
*vars
)
189 memset(vars
, 0, sizeof(*vars
));
192 static void codel_stats_init(struct codel_stats
*stats
)
194 stats
->maxpacket
= 0;
198 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
199 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
201 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
203 static void codel_Newton_step(struct codel_vars
*vars
)
205 u32 invsqrt
= ((u32
)vars
->rec_inv_sqrt
) << REC_INV_SQRT_SHIFT
;
206 u32 invsqrt2
= ((u64
)invsqrt
* invsqrt
) >> 32;
207 u64 val
= (3LL << 32) - ((u64
)vars
->count
* invsqrt2
);
209 val
>>= 2; /* avoid overflow in following multiply */
210 val
= (val
* invsqrt
) >> (32 - 2 + 1);
212 vars
->rec_inv_sqrt
= val
>> REC_INV_SQRT_SHIFT
;
216 * CoDel control_law is t + interval/sqrt(count)
217 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
218 * both sqrt() and divide operation.
220 static codel_time_t
codel_control_law(codel_time_t t
,
221 codel_time_t interval
,
224 return t
+ reciprocal_scale(interval
, rec_inv_sqrt
<< REC_INV_SQRT_SHIFT
);
227 typedef u32 (*codel_skb_len_t
)(const struct sk_buff
*skb
);
228 typedef codel_time_t (*codel_skb_time_t
)(const struct sk_buff
*skb
);
229 typedef void (*codel_skb_drop_t
)(struct sk_buff
*skb
, void *ctx
);
230 typedef struct sk_buff
* (*codel_skb_dequeue_t
)(struct codel_vars
*vars
,
233 static bool codel_should_drop(const struct sk_buff
*skb
,
235 struct codel_vars
*vars
,
236 struct codel_params
*params
,
237 struct codel_stats
*stats
,
238 codel_skb_len_t skb_len_func
,
239 codel_skb_time_t skb_time_func
,
247 vars
->first_above_time
= 0;
251 skb_len
= skb_len_func(skb
);
252 vars
->ldelay
= now
- skb_time_func(skb
);
254 if (unlikely(skb_len
> stats
->maxpacket
))
255 stats
->maxpacket
= skb_len
;
257 if (codel_time_before(vars
->ldelay
, params
->target
) ||
258 *backlog
<= params
->mtu
) {
259 /* went below - stay below for at least interval */
260 vars
->first_above_time
= 0;
264 if (vars
->first_above_time
== 0) {
265 /* just went above from below. If we stay above
266 * for at least interval we'll say it's ok to drop
268 vars
->first_above_time
= now
+ params
->interval
;
269 } else if (codel_time_after(now
, vars
->first_above_time
)) {
275 static struct sk_buff
*codel_dequeue(void *ctx
,
277 struct codel_params
*params
,
278 struct codel_vars
*vars
,
279 struct codel_stats
*stats
,
280 codel_skb_len_t skb_len_func
,
281 codel_skb_time_t skb_time_func
,
282 codel_skb_drop_t drop_func
,
283 codel_skb_dequeue_t dequeue_func
)
285 struct sk_buff
*skb
= dequeue_func(vars
, ctx
);
290 vars
->dropping
= false;
293 now
= codel_get_time();
294 drop
= codel_should_drop(skb
, ctx
, vars
, params
, stats
,
295 skb_len_func
, skb_time_func
, backlog
, now
);
296 if (vars
->dropping
) {
298 /* sojourn time below target - leave dropping state */
299 vars
->dropping
= false;
300 } else if (codel_time_after_eq(now
, vars
->drop_next
)) {
301 /* It's time for the next drop. Drop the current
302 * packet and dequeue the next. The dequeue might
303 * take us out of dropping state.
304 * If not, schedule the next drop.
305 * A large backlog might result in drop rates so high
306 * that the next drop should happen now,
307 * hence the while loop.
309 while (vars
->dropping
&&
310 codel_time_after_eq(now
, vars
->drop_next
)) {
311 vars
->count
++; /* dont care of possible wrap
312 * since there is no more divide
314 codel_Newton_step(vars
);
315 if (params
->ecn
&& INET_ECN_set_ce(skb
)) {
318 codel_control_law(vars
->drop_next
,
323 stats
->drop_len
+= skb_len_func(skb
);
326 skb
= dequeue_func(vars
, ctx
);
327 if (!codel_should_drop(skb
, ctx
,
332 /* leave dropping state */
333 vars
->dropping
= false;
335 /* and schedule the next drop */
337 codel_control_law(vars
->drop_next
,
346 if (params
->ecn
&& INET_ECN_set_ce(skb
)) {
349 stats
->drop_len
+= skb_len_func(skb
);
353 skb
= dequeue_func(vars
, ctx
);
354 drop
= codel_should_drop(skb
, ctx
, vars
, params
,
356 skb_time_func
, backlog
, now
);
358 vars
->dropping
= true;
359 /* if min went above target close to when we last went below it
360 * assume that the drop rate that controlled the queue on the
361 * last cycle is a good starting point to control it now.
363 delta
= vars
->count
- vars
->lastcount
;
365 codel_time_before(now
- vars
->drop_next
,
366 16 * params
->interval
)) {
368 /* we dont care if rec_inv_sqrt approximation
369 * is not very precise :
370 * Next Newton steps will correct it quadratically.
372 codel_Newton_step(vars
);
375 vars
->rec_inv_sqrt
= ~0U >> REC_INV_SQRT_SHIFT
;
377 vars
->lastcount
= vars
->count
;
378 vars
->drop_next
= codel_control_law(now
, params
->interval
,
382 if (skb
&& codel_time_after(vars
->ldelay
, params
->ce_threshold
) &&
383 INET_ECN_set_ce(skb
))