[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>
#include <linux/reciprocal_div.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_to_ns(ktime_get());

	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_divide(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>
536edd67	49	#include <linux/reciprocal_div.h>
76e3cc12 ED	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
1ba3aab3 JDB	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)
76e3cc12 ED	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
536edd67	138	* @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
76e3cc12 ED	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;
6ff272c9 ED	147	bool dropping;
6ff272c9 ED	148	u16 rec_inv_sqrt;
76e3cc12 ED	149	codel_time_t first_above_time;
	150	codel_time_t drop_next;
	151	codel_time_t ldelay;
	152	};
	153
6ff272c9 ED	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
76e3cc12 ED	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	{
536edd67	179	memset(vars, 0, sizeof(*vars));
76e3cc12 ED	180	}
	181
	182	static void codel_stats_init(struct codel_stats *stats)
	183	{
	184	stats->maxpacket = 256;
	185	}
	186
536edd67 ED	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	*
6ff272c9	191	* Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
76e3cc12	192	*/
536edd67	193	static void codel_Newton_step(struct codel_vars *vars)
76e3cc12	194	{
6ff272c9 ED	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);
76e3cc12	198
6ff272c9 ED	199	val >>= 2; /* avoid overflow in following multiply */
6ff272c9 ED	200	val = (val * invsqrt) >> (32 - 2 + 1);
76e3cc12	201
6ff272c9	202	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
76e3cc12 ED	203	}
76e3cc12 ED	204
536edd67 ED	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	*/
76e3cc12 ED	210	static codel_time_t codel_control_law(codel_time_t t,
76e3cc12 ED	211	codel_time_t interval,
536edd67	212	u32 rec_inv_sqrt)
76e3cc12	213	{
6ff272c9	214	return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
76e3cc12 ED	215	}
	216
	217
536edd67	218	static bool codel_should_drop(const struct sk_buff *skb,
865ec552	219	struct Qdisc *sch,
76e3cc12 ED	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);
865ec552	233	sch->qstats.backlog -= qdisc_pkt_len(skb);
76e3cc12 ED	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) \|\|
865ec552	239	sch->qstats.backlog <= stats->maxpacket) {
76e3cc12 ED	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,
865ec552	263	codel_skb_dequeue_t dequeue_func)
76e3cc12 ED	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();
865ec552	274	drop = codel_should_drop(skb, sch, vars, params, stats, now);
76e3cc12 ED	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)) {
536edd67 ED	290	vars->count++; /* dont care of possible wrap
	291	* since there is no more divide
	292	*/
	293	codel_Newton_step(vars);
76e3cc12 ED	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,
536edd67	299	vars->rec_inv_sqrt);
76e3cc12 ED	300	goto end;
	301	}
	302	qdisc_drop(skb, sch);
	303	stats->drop_count++;
	304	skb = dequeue_func(vars, sch);
865ec552	305	if (!codel_should_drop(skb, sch,
76e3cc12 ED	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,
536edd67	314	vars->rec_inv_sqrt);
76e3cc12 ED	315	}
	316	}
	317	}
	318	} else if (drop) {
2359a476 ED	319	u32 delta;
2359a476 ED	320
76e3cc12 ED	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);
865ec552	328	drop = codel_should_drop(skb, sch, vars, params,
76e3cc12 ED	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	*/
2359a476 ED	336	delta = vars->count - vars->lastcount;
	337	if (delta > 1 &&
	338	codel_time_before(now - vars->drop_next,
76e3cc12	339	16 * params->interval)) {
2359a476	340	vars->count = delta;
536edd67 ED	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);
76e3cc12 ED	346	} else {
76e3cc12 ED	347	vars->count = 1;
6ff272c9	348	vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
76e3cc12 ED	349	}
	350	vars->lastcount = vars->count;
	351	vars->drop_next = codel_control_law(now, params->interval,
536edd67	352	vars->rec_inv_sqrt);
76e3cc12 ED	353	}
	354	end:
	355	return skb;
	356	}
	357	#endif