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
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
90/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
91struct codel_skb_cb {
92	codel_time_t enqueue_time;
93};
94
95static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
96{
97	qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
98	return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
99}
100
101static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
102{
103	return get_codel_cb(skb)->enqueue_time;
104}
105
106static void codel_set_enqueue_time(struct sk_buff *skb)
107{
108	get_codel_cb(skb)->enqueue_time = codel_get_time();
109}
110
111static inline u32 codel_time_to_us(codel_time_t val)
112{
113	u64 valns = ((u64)val << CODEL_SHIFT);
114
115	do_div(valns, NSEC_PER_USEC);
116	return (u32)valns;
117}
118
119/**
120 * struct codel_params - contains codel parameters
121 * @target:	target queue size (in time units)
122 * @interval:	width of moving time window
123 * @mtu:	device mtu, or minimal queue backlog in bytes.
124 * @ecn:	is Explicit Congestion Notification enabled
125 */
126struct codel_params {
127	codel_time_t	target;
128	codel_time_t	interval;
129	u32		mtu;
130	bool		ecn;
131};
132
133/**
134 * struct codel_vars - contains codel variables
135 * @count:		how many drops we've done since the last time we
136 *			entered dropping state
137 * @lastcount:		count at entry to dropping state
138 * @dropping:		set to true if in dropping state
139 * @rec_inv_sqrt:	reciprocal value of sqrt(count) >> 1
140 * @first_above_time:	when we went (or will go) continuously above target
141 *			for interval
142 * @drop_next:		time to drop next packet, or when we dropped last
143 * @ldelay:		sojourn time of last dequeued packet
144 */
145struct codel_vars {
146	u32		count;
147	u32		lastcount;
148	bool		dropping;
149	u16		rec_inv_sqrt;
150	codel_time_t	first_above_time;
151	codel_time_t	drop_next;
152	codel_time_t	ldelay;
153};
154
155#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
156/* needed shift to get a Q0.32 number from rec_inv_sqrt */
157#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
158
159/**
160 * struct codel_stats - contains codel shared variables and stats
161 * @maxpacket:	largest packet we've seen so far
162 * @drop_count:	temp count of dropped packets in dequeue()
163 * ecn_mark:	number of packets we ECN marked instead of dropping
164 */
165struct codel_stats {
166	u32		maxpacket;
167	u32		drop_count;
168	u32		ecn_mark;
169};
170
171static void codel_params_init(struct codel_params *params,
172			      const struct Qdisc *sch)
173{
174	params->interval = MS2TIME(100);
175	params->target = MS2TIME(5);
176	params->mtu = psched_mtu(qdisc_dev(sch));
177	params->ecn = false;
178}
179
180static void codel_vars_init(struct codel_vars *vars)
181{
182	memset(vars, 0, sizeof(*vars));
183}
184
185static void codel_stats_init(struct codel_stats *stats)
186{
187	stats->maxpacket = 0;
188}
189
190/*
191 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
192 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
193 *
194 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
195 */
196static void codel_Newton_step(struct codel_vars *vars)
197{
198	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
199	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
200	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
201
202	val >>= 2; /* avoid overflow in following multiply */
203	val = (val * invsqrt) >> (32 - 2 + 1);
204
205	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
206}
207
208/*
209 * CoDel control_law is t + interval/sqrt(count)
210 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
211 * both sqrt() and divide operation.
212 */
213static codel_time_t codel_control_law(codel_time_t t,
214				      codel_time_t interval,
215				      u32 rec_inv_sqrt)
216{
217	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
218}
219
220static bool codel_should_drop(const struct sk_buff *skb,
221			      struct Qdisc *sch,
222			      struct codel_vars *vars,
223			      struct codel_params *params,
224			      struct codel_stats *stats,
225			      codel_time_t now)
226{
227	bool ok_to_drop;
228
229	if (!skb) {
230		vars->first_above_time = 0;
231		return false;
232	}
233
234	vars->ldelay = now - codel_get_enqueue_time(skb);
235	sch->qstats.backlog -= qdisc_pkt_len(skb);
236
237	if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
238		stats->maxpacket = qdisc_pkt_len(skb);
239
240	if (codel_time_before(vars->ldelay, params->target) ||
241	    sch->qstats.backlog <= params->mtu) {
242		/* went below - stay below for at least interval */
243		vars->first_above_time = 0;
244		return false;
245	}
246	ok_to_drop = false;
247	if (vars->first_above_time == 0) {
248		/* just went above from below. If we stay above
249		 * for at least interval we'll say it's ok to drop
250		 */
251		vars->first_above_time = now + params->interval;
252	} else if (codel_time_after(now, vars->first_above_time)) {
253		ok_to_drop = true;
254	}
255	return ok_to_drop;
256}
257
258typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
259						struct Qdisc *sch);
260
261static struct sk_buff *codel_dequeue(struct Qdisc *sch,
262				     struct codel_params *params,
263				     struct codel_vars *vars,
264				     struct codel_stats *stats,
265				     codel_skb_dequeue_t dequeue_func)
266{
267	struct sk_buff *skb = dequeue_func(vars, sch);
268	codel_time_t now;
269	bool drop;
270
271	if (!skb) {
272		vars->dropping = false;
273		return skb;
274	}
275	now = codel_get_time();
276	drop = codel_should_drop(skb, sch, vars, params, stats, now);
277	if (vars->dropping) {
278		if (!drop) {
279			/* sojourn time below target - leave dropping state */
280			vars->dropping = false;
281		} else if (codel_time_after_eq(now, vars->drop_next)) {
282			/* It's time for the next drop. Drop the current
283			 * packet and dequeue the next. The dequeue might
284			 * take us out of dropping state.
285			 * If not, schedule the next drop.
286			 * A large backlog might result in drop rates so high
287			 * that the next drop should happen now,
288			 * hence the while loop.
289			 */
290			while (vars->dropping &&
291			       codel_time_after_eq(now, vars->drop_next)) {
292				vars->count++; /* dont care of possible wrap
293						* since there is no more divide
294						*/
295				codel_Newton_step(vars);
296				if (params->ecn && INET_ECN_set_ce(skb)) {
297					stats->ecn_mark++;
298					vars->drop_next =
299						codel_control_law(vars->drop_next,
300								  params->interval,
301								  vars->rec_inv_sqrt);
302					goto end;
303				}
304				qdisc_drop(skb, sch);
305				stats->drop_count++;
306				skb = dequeue_func(vars, sch);
307				if (!codel_should_drop(skb, sch,
308						       vars, params, stats, now)) {
309					/* leave dropping state */
310					vars->dropping = false;
311				} else {
312					/* and schedule the next drop */
313					vars->drop_next =
314						codel_control_law(vars->drop_next,
315								  params->interval,
316								  vars->rec_inv_sqrt);
317				}
318			}
319		}
320	} else if (drop) {
321		u32 delta;
322
323		if (params->ecn && INET_ECN_set_ce(skb)) {
324			stats->ecn_mark++;
325		} else {
326			qdisc_drop(skb, sch);
327			stats->drop_count++;
328
329			skb = dequeue_func(vars, sch);
330			drop = codel_should_drop(skb, sch, vars, params,
331						 stats, now);
332		}
333		vars->dropping = true;
334		/* if min went above target close to when we last went below it
335		 * assume that the drop rate that controlled the queue on the
336		 * last cycle is a good starting point to control it now.
337		 */
338		delta = vars->count - vars->lastcount;
339		if (delta > 1 &&
340		    codel_time_before(now - vars->drop_next,
341				      16 * params->interval)) {
342			vars->count = delta;
343			/* we dont care if rec_inv_sqrt approximation
344			 * is not very precise :
345			 * Next Newton steps will correct it quadratically.
346			 */
347			codel_Newton_step(vars);
348		} else {
349			vars->count = 1;
350			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
351		}
352		vars->lastcount = vars->count;
353		vars->drop_next = codel_control_law(now, params->interval,
354						    vars->rec_inv_sqrt);
355	}
356end:
357	return skb;
358}
359#endif
360