[mirror_ubuntu-bionic-kernel.git] / include / net / codel.h

#ifndef __NET_SCHED_CODEL_H
#define __NET_SCHED_CODEL_H

/*
 * Codel - The Controlled-Delay Active Queue Management algorithm
 *
 *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
 *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
 *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
 *  Copyright (C) 2012 Eric Dumazet <edumazet@google.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The names of the authors may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 */

#include <linux/types.h>
#include <linux/ktime.h>
#include <linux/skbuff.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>

/* Controlling Queue Delay (CoDel) algorithm
 * =========================================
 * Source : Kathleen Nichols and Van Jacobson
 * http://queue.acm.org/detail.cfm?id=2209336
 *
 * Implemented on linux by Dave Taht and Eric Dumazet
 */


/* CoDel uses a 1024 nsec clock, encoded in u32
 * This gives a range of 2199 seconds, because of signed compares
 */
typedef u32 codel_time_t;
typedef s32 codel_tdiff_t;
#define CODEL_SHIFT 10
#define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)

static inline codel_time_t codel_get_time(void)
{
	u64 ns = ktime_get_ns();

	return ns >> CODEL_SHIFT;
}

/* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia:
 *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
 * codel_time_after(a,b) returns true if the time a is after time b.
 */
#define codel_time_after(a, b)						\
	(typecheck(codel_time_t, a) &&					\
	 typecheck(codel_time_t, b) &&					\
	 ((s32)((a) - (b)) > 0))
#define codel_time_before(a, b) 	codel_time_after(b, a)

#define codel_time_after_eq(a, b)					\
	(typecheck(codel_time_t, a) &&					\
	 typecheck(codel_time_t, b) &&					\
	 ((s32)((a) - (b)) >= 0))
#define codel_time_before_eq(a, b)	codel_time_after_eq(b, a)

/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
struct codel_skb_cb {
	codel_time_t enqueue_time;
};

static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
{
	qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
	return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
}

static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
{
	return get_codel_cb(skb)->enqueue_time;
}

static void codel_set_enqueue_time(struct sk_buff *skb)
{
	get_codel_cb(skb)->enqueue_time = codel_get_time();
}

static inline u32 codel_time_to_us(codel_time_t val)
{
	u64 valns = ((u64)val << CODEL_SHIFT);

	do_div(valns, NSEC_PER_USEC);
	return (u32)valns;
}

/**
 * struct codel_params - contains codel parameters
 * @target:	target queue size (in time units)
 * @interval:	width of moving time window
 * @ecn:	is Explicit Congestion Notification enabled
 */
struct codel_params {
	codel_time_t	target;
	codel_time_t	interval;
	bool		ecn;
};

/**
 * struct codel_vars - contains codel variables
 * @count:		how many drops we've done since the last time we
 *			entered dropping state
 * @lastcount:		count at entry to dropping state
 * @dropping:		set to true if in dropping state
 * @rec_inv_sqrt:	reciprocal value of sqrt(count) >> 1
 * @first_above_time:	when we went (or will go) continuously above target
 *			for interval
 * @drop_next:		time to drop next packet, or when we dropped last
 * @ldelay:		sojourn time of last dequeued packet
 */
struct codel_vars {
	u32		count;
	u32		lastcount;
	bool		dropping;
	u16		rec_inv_sqrt;
	codel_time_t	first_above_time;
	codel_time_t	drop_next;
	codel_time_t	ldelay;
};

#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
/* needed shift to get a Q0.32 number from rec_inv_sqrt */
#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)

/**
 * struct codel_stats - contains codel shared variables and stats
 * @maxpacket:	largest packet we've seen so far
 * @drop_count:	temp count of dropped packets in dequeue()
 * ecn_mark:	number of packets we ECN marked instead of dropping
 */
struct codel_stats {
	u32		maxpacket;
	u32		drop_count;
	u32		ecn_mark;
};

static void codel_params_init(struct codel_params *params)
{
	params->interval = MS2TIME(100);
	params->target = MS2TIME(5);
	params->ecn = false;
}

static void codel_vars_init(struct codel_vars *vars)
{
	memset(vars, 0, sizeof(*vars));
}

static void codel_stats_init(struct codel_stats *stats)
{
	stats->maxpacket = 256;
}

/*
 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
 *
 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
 */
static void codel_Newton_step(struct codel_vars *vars)
{
	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);

	val >>= 2; /* avoid overflow in following multiply */
	val = (val * invsqrt) >> (32 - 2 + 1);

	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
}

/*
 * CoDel control_law is t + interval/sqrt(count)
 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
 * both sqrt() and divide operation.
 */
static codel_time_t codel_control_law(codel_time_t t,
				      codel_time_t interval,
				      u32 rec_inv_sqrt)
{
	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
}

static bool codel_should_drop(const struct sk_buff *skb,
			      struct Qdisc *sch,
			      struct codel_vars *vars,
			      struct codel_params *params,
			      struct codel_stats *stats,
			      codel_time_t now)
{
	bool ok_to_drop;

	if (!skb) {
		vars->first_above_time = 0;
		return false;
	}

	vars->ldelay = now - codel_get_enqueue_time(skb);
	sch->qstats.backlog -= qdisc_pkt_len(skb);

	if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
		stats->maxpacket = qdisc_pkt_len(skb);

	if (codel_time_before(vars->ldelay, params->target) ||
	    sch->qstats.backlog <= stats->maxpacket) {
		/* went below - stay below for at least interval */
		vars->first_above_time = 0;
		return false;
	}
	ok_to_drop = false;
	if (vars->first_above_time == 0) {
		/* just went above from below. If we stay above
		 * for at least interval we'll say it's ok to drop
		 */
		vars->first_above_time = now + params->interval;
	} else if (codel_time_after(now, vars->first_above_time)) {
		ok_to_drop = true;
	}
	return ok_to_drop;
}

typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
						struct Qdisc *sch);

static struct sk_buff *codel_dequeue(struct Qdisc *sch,
				     struct codel_params *params,
				     struct codel_vars *vars,
				     struct codel_stats *stats,
				     codel_skb_dequeue_t dequeue_func)
{
	struct sk_buff *skb = dequeue_func(vars, sch);
	codel_time_t now;
	bool drop;

	if (!skb) {
		vars->dropping = false;
		return skb;
	}
	now = codel_get_time();
	drop = codel_should_drop(skb, sch, vars, params, stats, now);
	if (vars->dropping) {
		if (!drop) {
			/* sojourn time below target - leave dropping state */
			vars->dropping = false;
		} else if (codel_time_after_eq(now, vars->drop_next)) {
			/* It's time for the next drop. Drop the current
			 * packet and dequeue the next. The dequeue might
			 * take us out of dropping state.
			 * If not, schedule the next drop.
			 * A large backlog might result in drop rates so high
			 * that the next drop should happen now,
			 * hence the while loop.
			 */
			while (vars->dropping &&
			       codel_time_after_eq(now, vars->drop_next)) {
				vars->count++; /* dont care of possible wrap
						* since there is no more divide
						*/
				codel_Newton_step(vars);
				if (params->ecn && INET_ECN_set_ce(skb)) {
					stats->ecn_mark++;
					vars->drop_next =
						codel_control_law(vars->drop_next,
								  params->interval,
								  vars->rec_inv_sqrt);
					goto end;
				}
				qdisc_drop(skb, sch);
				stats->drop_count++;
				skb = dequeue_func(vars, sch);
				if (!codel_should_drop(skb, sch,
						       vars, params, stats, now)) {
					/* leave dropping state */
					vars->dropping = false;
				} else {
					/* and schedule the next drop */
					vars->drop_next =
						codel_control_law(vars->drop_next,
								  params->interval,
								  vars->rec_inv_sqrt);
				}
			}
		}
	} else if (drop) {
		u32 delta;

		if (params->ecn && INET_ECN_set_ce(skb)) {
			stats->ecn_mark++;
		} else {
			qdisc_drop(skb, sch);
			stats->drop_count++;

			skb = dequeue_func(vars, sch);
			drop = codel_should_drop(skb, sch, vars, params,
						 stats, now);
		}
		vars->dropping = true;
		/* if min went above target close to when we last went below it
		 * assume that the drop rate that controlled the queue on the
		 * last cycle is a good starting point to control it now.
		 */
		delta = vars->count - vars->lastcount;
		if (delta > 1 &&
		    codel_time_before(now - vars->drop_next,
				      16 * params->interval)) {
			vars->count = delta;
			/* we dont care if rec_inv_sqrt approximation
			 * is not very precise :
			 * Next Newton steps will correct it quadratically.
			 */
			codel_Newton_step(vars);
		} else {
			vars->count = 1;
			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
		}
		vars->lastcount = vars->count;
		vars->drop_next = codel_control_law(now, params->interval,
						    vars->rec_inv_sqrt);
	}
end:
	return skb;
}
#endif
Commit	Line	Data
76e3cc12 ED	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	*/
	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)
66
67	static inline codel_time_t codel_get_time(void)
68	{
d2de875c	69	u64 ns = ktime_get_ns();
76e3cc12 ED	70
	71	return ns >> CODEL_SHIFT;
	72	}
	73
1ba3aab3 JDB	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)
76e3cc12 ED	89
	90	/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
	91	struct codel_skb_cb {
	92	codel_time_t enqueue_time;
	93	};
	94
	95	static 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
	101	static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
	102	{
	103	return get_codel_cb(skb)->enqueue_time;
	104	}
	105
	106	static void codel_set_enqueue_time(struct sk_buff *skb)
	107	{
	108	get_codel_cb(skb)->enqueue_time = codel_get_time();
	109	}
	110
	111	static 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	* @ecn: is Explicit Congestion Notification enabled
	124	*/
	125	struct codel_params {
	126	codel_time_t target;
	127	codel_time_t interval;
	128	bool ecn;
	129	};
	130
	131	/**
	132	* struct codel_vars - contains codel variables
	133	* @count: how many drops we've done since the last time we
	134	* entered dropping state
	135	* @lastcount: count at entry to dropping state
	136	* @dropping: set to true if in dropping state
536edd67	137	* @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
76e3cc12 ED	138	* @first_above_time: when we went (or will go) continuously above target
	139	* for interval
	140	* @drop_next: time to drop next packet, or when we dropped last
	141	* @ldelay: sojourn time of last dequeued packet
	142	*/
	143	struct codel_vars {
	144	u32 count;
	145	u32 lastcount;
6ff272c9 ED	146	bool dropping;
6ff272c9 ED	147	u16 rec_inv_sqrt;
76e3cc12 ED	148	codel_time_t first_above_time;
	149	codel_time_t drop_next;
	150	codel_time_t ldelay;
	151	};
	152
6ff272c9 ED	153	#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
	154	/* needed shift to get a Q0.32 number from rec_inv_sqrt */
	155	#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
	156
76e3cc12 ED	157	/**
	158	* struct codel_stats - contains codel shared variables and stats
	159	* @maxpacket: largest packet we've seen so far
	160	* @drop_count: temp count of dropped packets in dequeue()
	161	* ecn_mark: number of packets we ECN marked instead of dropping
	162	*/
	163	struct codel_stats {
	164	u32 maxpacket;
	165	u32 drop_count;
	166	u32 ecn_mark;
	167	};
	168
	169	static void codel_params_init(struct codel_params *params)
	170	{
	171	params->interval = MS2TIME(100);
	172	params->target = MS2TIME(5);
	173	params->ecn = false;
	174	}
	175
	176	static void codel_vars_init(struct codel_vars *vars)
	177	{
536edd67	178	memset(vars, 0, sizeof(*vars));
76e3cc12 ED	179	}
	180
	181	static void codel_stats_init(struct codel_stats *stats)
	182	{
	183	stats->maxpacket = 256;
	184	}
	185
536edd67 ED	186	/*
	187	* http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
	188	* new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
	189	*
6ff272c9	190	* Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
76e3cc12	191	*/
536edd67	192	static void codel_Newton_step(struct codel_vars *vars)
76e3cc12	193	{
6ff272c9 ED	194	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
	195	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
	196	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
76e3cc12	197
6ff272c9 ED	198	val >>= 2; /* avoid overflow in following multiply */
6ff272c9 ED	199	val = (val * invsqrt) >> (32 - 2 + 1);
76e3cc12	200
6ff272c9	201	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
76e3cc12 ED	202	}
76e3cc12 ED	203
536edd67 ED	204	/*
	205	* CoDel control_law is t + interval/sqrt(count)
	206	* We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
	207	* both sqrt() and divide operation.
	208	*/
76e3cc12 ED	209	static codel_time_t codel_control_law(codel_time_t t,
76e3cc12 ED	210	codel_time_t interval,
536edd67	211	u32 rec_inv_sqrt)
76e3cc12	212	{
89770b0a	213	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
76e3cc12 ED	214	}
76e3cc12 ED	215
536edd67	216	static bool codel_should_drop(const struct sk_buff *skb,
865ec552	217	struct Qdisc *sch,
76e3cc12 ED	218	struct codel_vars *vars,
	219	struct codel_params *params,
	220	struct codel_stats *stats,
	221	codel_time_t now)
	222	{
	223	bool ok_to_drop;
	224
	225	if (!skb) {
	226	vars->first_above_time = 0;
	227	return false;
	228	}
	229
	230	vars->ldelay = now - codel_get_enqueue_time(skb);
865ec552	231	sch->qstats.backlog -= qdisc_pkt_len(skb);
76e3cc12 ED	232
	233	if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
	234	stats->maxpacket = qdisc_pkt_len(skb);
	235
	236	if (codel_time_before(vars->ldelay, params->target) \|\|
865ec552	237	sch->qstats.backlog <= stats->maxpacket) {
76e3cc12 ED	238	/* went below - stay below for at least interval */
	239	vars->first_above_time = 0;
	240	return false;
	241	}
	242	ok_to_drop = false;
	243	if (vars->first_above_time == 0) {
	244	/* just went above from below. If we stay above
	245	* for at least interval we'll say it's ok to drop
	246	*/
	247	vars->first_above_time = now + params->interval;
	248	} else if (codel_time_after(now, vars->first_above_time)) {
	249	ok_to_drop = true;
	250	}
	251	return ok_to_drop;
	252	}
	253
	254	typedef struct sk_buff * (codel_skb_dequeue_t)(struct codel_vars vars,
	255	struct Qdisc *sch);
	256
	257	static struct sk_buff codel_dequeue(struct Qdisc sch,
	258	struct codel_params *params,
	259	struct codel_vars *vars,
	260	struct codel_stats *stats,
865ec552	261	codel_skb_dequeue_t dequeue_func)
76e3cc12 ED	262	{
	263	struct sk_buff *skb = dequeue_func(vars, sch);
	264	codel_time_t now;
	265	bool drop;
	266
	267	if (!skb) {
	268	vars->dropping = false;
	269	return skb;
	270	}
	271	now = codel_get_time();
865ec552	272	drop = codel_should_drop(skb, sch, vars, params, stats, now);
76e3cc12 ED	273	if (vars->dropping) {
	274	if (!drop) {
	275	/* sojourn time below target - leave dropping state */
	276	vars->dropping = false;
	277	} else if (codel_time_after_eq(now, vars->drop_next)) {
	278	/* It's time for the next drop. Drop the current
	279	* packet and dequeue the next. The dequeue might
	280	* take us out of dropping state.
	281	* If not, schedule the next drop.
	282	* A large backlog might result in drop rates so high
	283	* that the next drop should happen now,
	284	* hence the while loop.
	285	*/
	286	while (vars->dropping &&
	287	codel_time_after_eq(now, vars->drop_next)) {
536edd67 ED	288	vars->count++; /* dont care of possible wrap
	289	* since there is no more divide
	290	*/
	291	codel_Newton_step(vars);
76e3cc12 ED	292	if (params->ecn && INET_ECN_set_ce(skb)) {
	293	stats->ecn_mark++;
	294	vars->drop_next =
	295	codel_control_law(vars->drop_next,
	296	params->interval,
536edd67	297	vars->rec_inv_sqrt);
76e3cc12 ED	298	goto end;
	299	}
	300	qdisc_drop(skb, sch);
	301	stats->drop_count++;
	302	skb = dequeue_func(vars, sch);
865ec552	303	if (!codel_should_drop(skb, sch,
76e3cc12 ED	304	vars, params, stats, now)) {
	305	/* leave dropping state */
	306	vars->dropping = false;
	307	} else {
	308	/* and schedule the next drop */
	309	vars->drop_next =
	310	codel_control_law(vars->drop_next,
	311	params->interval,
536edd67	312	vars->rec_inv_sqrt);
76e3cc12 ED	313	}
	314	}
	315	}
	316	} else if (drop) {
2359a476 ED	317	u32 delta;
2359a476 ED	318
76e3cc12 ED	319	if (params->ecn && INET_ECN_set_ce(skb)) {
	320	stats->ecn_mark++;
	321	} else {
	322	qdisc_drop(skb, sch);
	323	stats->drop_count++;
	324
	325	skb = dequeue_func(vars, sch);
865ec552	326	drop = codel_should_drop(skb, sch, vars, params,
76e3cc12 ED	327	stats, now);
	328	}
	329	vars->dropping = true;
	330	/* if min went above target close to when we last went below it
	331	* assume that the drop rate that controlled the queue on the
	332	* last cycle is a good starting point to control it now.
	333	*/
2359a476 ED	334	delta = vars->count - vars->lastcount;
	335	if (delta > 1 &&
	336	codel_time_before(now - vars->drop_next,
76e3cc12	337	16 * params->interval)) {
2359a476	338	vars->count = delta;
536edd67 ED	339	/* we dont care if rec_inv_sqrt approximation
	340	* is not very precise :
	341	* Next Newton steps will correct it quadratically.
	342	*/
	343	codel_Newton_step(vars);
76e3cc12 ED	344	} else {
76e3cc12 ED	345	vars->count = 1;
6ff272c9	346	vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
76e3cc12 ED	347	}
	348	vars->lastcount = vars->count;
	349	vars->drop_next = codel_control_law(now, params->interval,
536edd67	350	vars->rec_inv_sqrt);
76e3cc12 ED	351	}
	352	end:
	353	return skb;
	354	}
	355	#endif