[linux.git] / include / net / red.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __NET_SCHED_RED_H
#define __NET_SCHED_RED_H

#include <linux/types.h>
#include <linux/bug.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>
#include <net/dsfield.h>
#include <linux/reciprocal_div.h>

/*	Random Early Detection (RED) algorithm.
	=======================================

	Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
	for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.

	This file codes a "divisionless" version of RED algorithm
	as written down in Fig.17 of the paper.

	Short description.
	------------------

	When a new packet arrives we calculate the average queue length:

	avg = (1-W)*avg + W*current_queue_len,

	W is the filter time constant (chosen as 2^(-Wlog)), it controls
	the inertia of the algorithm. To allow larger bursts, W should be
	decreased.

	if (avg > th_max) -> packet marked (dropped).
	if (avg < th_min) -> packet passes.
	if (th_min < avg < th_max) we calculate probability:

	Pb = max_P * (avg - th_min)/(th_max-th_min)

	and mark (drop) packet with this probability.
	Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
	max_P should be small (not 1), usually 0.01..0.02 is good value.

	max_P is chosen as a number, so that max_P/(th_max-th_min)
	is a negative power of two in order arithmetics to contain
	only shifts.


	Parameters, settable by user:
	-----------------------------

	qth_min		- bytes (should be < qth_max/2)
	qth_max		- bytes (should be at least 2*qth_min and less limit)
	Wlog	       	- bits (<32) log(1/W).
	Plog	       	- bits (<32)

	Plog is related to max_P by formula:

	max_P = (qth_max-qth_min)/2^Plog;

	F.e. if qth_max=128K and qth_min=32K, then Plog=22
	corresponds to max_P=0.02

	Scell_log
	Stab

	Lookup table for log((1-W)^(t/t_ave).


	NOTES:

	Upper bound on W.
	-----------------

	If you want to allow bursts of L packets of size S,
	you should choose W:

	L + 1 - th_min/S < (1-(1-W)^L)/W

	th_min/S = 32         th_min/S = 4

	log(W)	L
	-1	33
	-2	35
	-3	39
	-4	46
	-5	57
	-6	75
	-7	101
	-8	135
	-9	190
	etc.
 */

/*
 * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
 * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
 *
 * Every 500 ms:
 *  if (avg > target and max_p <= 0.5)
 *   increase max_p : max_p += alpha;
 *  else if (avg < target and max_p >= 0.01)
 *   decrease max_p : max_p *= beta;
 *
 * target :[qth_min + 0.4*(qth_min - qth_max),
 *          qth_min + 0.6*(qth_min - qth_max)].
 * alpha : min(0.01, max_p / 4)
 * beta : 0.9
 * max_P is a Q0.32 fixed point number (with 32 bits mantissa)
 * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
 */
#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))

#define MAX_P_MIN (1 * RED_ONE_PERCENT)
#define MAX_P_MAX (50 * RED_ONE_PERCENT)
#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)

#define RED_STAB_SIZE	256
#define RED_STAB_MASK	(RED_STAB_SIZE - 1)

struct red_stats {
	u32		prob_drop;	/* Early probability drops */
	u32		prob_mark;	/* Early probability marks */
	u32		forced_drop;	/* Forced drops, qavg > max_thresh */
	u32		forced_mark;	/* Forced marks, qavg > max_thresh */
	u32		pdrop;          /* Drops due to queue limits */
	u32		other;          /* Drops due to drop() calls */
};

struct red_parms {
	/* Parameters */
	u32		qth_min;	/* Min avg length threshold: Wlog scaled */
	u32		qth_max;	/* Max avg length threshold: Wlog scaled */
	u32		Scell_max;
	u32		max_P;		/* probability, [0 .. 1.0] 32 scaled */
	/* reciprocal_value(max_P / qth_delta) */
	struct reciprocal_value	max_P_reciprocal;
	u32		qth_delta;	/* max_th - min_th */
	u32		target_min;	/* min_th + 0.4*(max_th - min_th) */
	u32		target_max;	/* min_th + 0.6*(max_th - min_th) */
	u8		Scell_log;
	u8		Wlog;		/* log(W)		*/
	u8		Plog;		/* random number bits	*/
	u8		Stab[RED_STAB_SIZE];
};

struct red_vars {
	/* Variables */
	int		qcount;		/* Number of packets since last random
					   number generation */
	u32		qR;		/* Cached random number */

	unsigned long	qavg;		/* Average queue length: Wlog scaled */
	ktime_t		qidlestart;	/* Start of current idle period */
};

static inline u32 red_maxp(u8 Plog)
{
	return Plog < 32 ? (~0U >> Plog) : ~0U;
}

static inline void red_set_vars(struct red_vars *v)
{
	/* Reset average queue length, the value is strictly bound
	 * to the parameters below, reseting hurts a bit but leaving
	 * it might result in an unreasonable qavg for a while. --TGR
	 */
	v->qavg		= 0;

	v->qcount	= -1;
}

static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog, u8 Scell_log)
{
	if (fls(qth_min) + Wlog > 32)
		return false;
	if (fls(qth_max) + Wlog > 32)
		return false;
	if (Scell_log >= 32)
		return false;
	if (qth_max < qth_min)
		return false;
	return true;
}

static inline int red_get_flags(unsigned char qopt_flags,
				unsigned char historic_mask,
				struct nlattr *flags_attr,
				unsigned char supported_mask,
				struct nla_bitfield32 *p_flags,
				unsigned char *p_userbits,
				struct netlink_ext_ack *extack)
{
	struct nla_bitfield32 flags;

	if (qopt_flags && flags_attr) {
		NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute");
		return -EINVAL;
	}

	if (flags_attr) {
		flags = nla_get_bitfield32(flags_attr);
	} else {
		flags.selector = historic_mask;
		flags.value = qopt_flags & historic_mask;
	}

	*p_flags = flags;
	*p_userbits = qopt_flags & ~historic_mask;
	return 0;
}

static inline int red_validate_flags(unsigned char flags,
				     struct netlink_ext_ack *extack)
{
	if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) {
		NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN");
		return -EINVAL;
	}

	return 0;
}

static inline void red_set_parms(struct red_parms *p,
				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
				 u8 Scell_log, u8 *stab, u32 max_P)
{
	int delta = qth_max - qth_min;
	u32 max_p_delta;

	p->qth_min	= qth_min << Wlog;
	p->qth_max	= qth_max << Wlog;
	p->Wlog		= Wlog;
	p->Plog		= Plog;
	if (delta <= 0)
		delta = 1;
	p->qth_delta	= delta;
	if (!max_P) {
		max_P = red_maxp(Plog);
		max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */
	}
	p->max_P = max_P;
	max_p_delta = max_P / delta;
	max_p_delta = max(max_p_delta, 1U);
	p->max_P_reciprocal  = reciprocal_value(max_p_delta);

	/* RED Adaptative target :
	 * [min_th + 0.4*(min_th - max_th),
	 *  min_th + 0.6*(min_th - max_th)].
	 */
	delta /= 5;
	p->target_min = qth_min + 2*delta;
	p->target_max = qth_min + 3*delta;

	p->Scell_log	= Scell_log;
	p->Scell_max	= (255 << Scell_log);

	if (stab)
		memcpy(p->Stab, stab, sizeof(p->Stab));
}

static inline int red_is_idling(const struct red_vars *v)
{
	return v->qidlestart != 0;
}

static inline void red_start_of_idle_period(struct red_vars *v)
{
	v->qidlestart = ktime_get();
}

static inline void red_end_of_idle_period(struct red_vars *v)
{
	v->qidlestart = 0;
}

static inline void red_restart(struct red_vars *v)
{
	red_end_of_idle_period(v);
	v->qavg = 0;
	v->qcount = -1;
}

static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
							 const struct red_vars *v)
{
	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
	long us_idle = min_t(s64, delta, p->Scell_max);
	int  shift;

	/*
	 * The problem: ideally, average length queue recalcultion should
	 * be done over constant clock intervals. This is too expensive, so
	 * that the calculation is driven by outgoing packets.
	 * When the queue is idle we have to model this clock by hand.
	 *
	 * SF+VJ proposed to "generate":
	 *
	 *	m = idletime / (average_pkt_size / bandwidth)
	 *
	 * dummy packets as a burst after idle time, i.e.
	 *
	 * 	v->qavg *= (1-W)^m
	 *
	 * This is an apparently overcomplicated solution (f.e. we have to
	 * precompute a table to make this calculation in reasonable time)
	 * I believe that a simpler model may be used here,
	 * but it is field for experiments.
	 */

	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];

	if (shift)
		return v->qavg >> shift;
	else {
		/* Approximate initial part of exponent with linear function:
		 *
		 * 	(1-W)^m ~= 1-mW + ...
		 *
		 * Seems, it is the best solution to
		 * problem of too coarse exponent tabulation.
		 */
		us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;

		if (us_idle < (v->qavg >> 1))
			return v->qavg - us_idle;
		else
			return v->qavg >> 1;
	}
}

static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
						       const struct red_vars *v,
						       unsigned int backlog)
{
	/*
	 * NOTE: v->qavg is fixed point number with point at Wlog.
	 * The formula below is equvalent to floating point
	 * version:
	 *
	 * 	qavg = qavg*(1-W) + backlog*W;
	 *
	 * --ANK (980924)
	 */
	return v->qavg + (backlog - (v->qavg >> p->Wlog));
}

static inline unsigned long red_calc_qavg(const struct red_parms *p,
					  const struct red_vars *v,
					  unsigned int backlog)
{
	if (!red_is_idling(v))
		return red_calc_qavg_no_idle_time(p, v, backlog);
	else
		return red_calc_qavg_from_idle_time(p, v);
}


static inline u32 red_random(const struct red_parms *p)
{
	return reciprocal_divide(prandom_u32(), p->max_P_reciprocal);
}

static inline int red_mark_probability(const struct red_parms *p,
				       const struct red_vars *v,
				       unsigned long qavg)
{
	/* The formula used below causes questions.

	   OK. qR is random number in the interval
		(0..1/max_P)*(qth_max-qth_min)
	   i.e. 0..(2^Plog). If we used floating point
	   arithmetics, it would be: (2^Plog)*rnd_num,
	   where rnd_num is less 1.

	   Taking into account, that qavg have fixed
	   point at Wlog, two lines
	   below have the following floating point equivalent:

	   max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount

	   Any questions? --ANK (980924)
	 */
	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
}

enum {
	RED_BELOW_MIN_THRESH,
	RED_BETWEEN_TRESH,
	RED_ABOVE_MAX_TRESH,
};

static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
{
	if (qavg < p->qth_min)
		return RED_BELOW_MIN_THRESH;
	else if (qavg >= p->qth_max)
		return RED_ABOVE_MAX_TRESH;
	else
		return RED_BETWEEN_TRESH;
}

enum {
	RED_DONT_MARK,
	RED_PROB_MARK,
	RED_HARD_MARK,
};

static inline int red_action(const struct red_parms *p,
			     struct red_vars *v,
			     unsigned long qavg)
{
	switch (red_cmp_thresh(p, qavg)) {
		case RED_BELOW_MIN_THRESH:
			v->qcount = -1;
			return RED_DONT_MARK;

		case RED_BETWEEN_TRESH:
			if (++v->qcount) {
				if (red_mark_probability(p, v, qavg)) {
					v->qcount = 0;
					v->qR = red_random(p);
					return RED_PROB_MARK;
				}
			} else
				v->qR = red_random(p);

			return RED_DONT_MARK;

		case RED_ABOVE_MAX_TRESH:
			v->qcount = -1;
			return RED_HARD_MARK;
	}

	BUG();
	return RED_DONT_MARK;
}

static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
{
	unsigned long qavg;
	u32 max_p_delta;

	qavg = v->qavg;
	if (red_is_idling(v))
		qavg = red_calc_qavg_from_idle_time(p, v);

	/* v->qavg is fixed point number with point at Wlog */
	qavg >>= p->Wlog;

	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
		p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
		p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */

	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
	max_p_delta = max(max_p_delta, 1U);
	p->max_P_reciprocal = reciprocal_value(max_p_delta);
}
#endif
Commit	Line	Data
b2441318	1	/* SPDX-License-Identifier: GPL-2.0 */
a7834745 TG	2	#ifndef __NET_SCHED_RED_H
	3	#define __NET_SCHED_RED_H
	4
a7834745	5	#include <linux/types.h>
187f1882	6	#include <linux/bug.h>
a7834745 TG	7	#include <net/pkt_sched.h>
	8	#include <net/inet_ecn.h>
	9	#include <net/dsfield.h>
8af2a218	10	#include <linux/reciprocal_div.h>
a7834745 TG	11
	12	/* Random Early Detection (RED) algorithm.
	13	=======================================
	14
	15	Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
	16	for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
	17
	18	This file codes a "divisionless" version of RED algorithm
	19	as written down in Fig.17 of the paper.
	20
	21	Short description.
	22	------------------
	23
	24	When a new packet arrives we calculate the average queue length:
	25
	26	avg = (1-W)avg + Wcurrent_queue_len,
	27
	28	W is the filter time constant (chosen as 2^(-Wlog)), it controls
	29	the inertia of the algorithm. To allow larger bursts, W should be
	30	decreased.
	31
	32	if (avg > th_max) -> packet marked (dropped).
	33	if (avg < th_min) -> packet passes.
	34	if (th_min < avg < th_max) we calculate probability:
	35
	36	Pb = max_P * (avg - th_min)/(th_max-th_min)
	37
	38	and mark (drop) packet with this probability.
	39	Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
	40	max_P should be small (not 1), usually 0.01..0.02 is good value.
	41
	42	max_P is chosen as a number, so that max_P/(th_max-th_min)
	43	is a negative power of two in order arithmetics to contain
	44	only shifts.
	45
	46
	47	Parameters, settable by user:
	48	-----------------------------
	49
	50	qth_min - bytes (should be < qth_max/2)
	51	qth_max - bytes (should be at least 2*qth_min and less limit)
	52	Wlog - bits (<32) log(1/W).
	53	Plog - bits (<32)
	54
	55	Plog is related to max_P by formula:
	56
	57	max_P = (qth_max-qth_min)/2^Plog;
	58
	59	F.e. if qth_max=128K and qth_min=32K, then Plog=22
	60	corresponds to max_P=0.02
	61
	62	Scell_log
	63	Stab
	64
	65	Lookup table for log((1-W)^(t/t_ave).
	66
	67
	68	NOTES:
	69
	70	Upper bound on W.
	71	-----------------
	72
	73	If you want to allow bursts of L packets of size S,
	74	you should choose W:
75
76	L + 1 - th_min/S < (1-(1-W)^L)/W
77
78	th_min/S = 32 th_min/S = 4
79
80	log(W) L
81	-1 33
82	-2 35
83	-3 39
84	-4 46
85	-5 57
86	-6 75
87	-7 101
88	-8 135
89	-9 190
90	etc.
91	*/
92
8af2a218 ED	93	/*
	94	* Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
	95	* (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
	96	*
	97	* Every 500 ms:
	98	* if (avg > target and max_p <= 0.5)
	99	* increase max_p : max_p += alpha;
	100	* else if (avg < target and max_p >= 0.01)
	101	* decrease max_p : max_p *= beta;
	102	*
	103	* target :[qth_min + 0.4*(qth_min - qth_max),
	104	* qth_min + 0.6*(qth_min - qth_max)].
	105	* alpha : min(0.01, max_p / 4)
	106	* beta : 0.9
	107	* max_P is a Q0.32 fixed point number (with 32 bits mantissa)
	108	* max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
	109	*/
	110	#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))
	111
	112	#define MAX_P_MIN (1 * RED_ONE_PERCENT)
	113	#define MAX_P_MAX (50 * RED_ONE_PERCENT)
	114	#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)
	115
a7834745 TG	116	#define RED_STAB_SIZE 256
	117	#define RED_STAB_MASK (RED_STAB_SIZE - 1)
	118
fd2c3ef7	119	struct red_stats {
a7834745 TG	120	u32 prob_drop; /* Early probability drops */
	121	u32 prob_mark; /* Early probability marks */
	122	u32 forced_drop; /* Forced drops, qavg > max_thresh */
	123	u32 forced_mark; /* Forced marks, qavg > max_thresh */
	124	u32 pdrop; /* Drops due to queue limits */
	125	u32 other; /* Drops due to drop() calls */
a7834745 TG	126	};
a7834745 TG	127
fd2c3ef7	128	struct red_parms {
a7834745	129	/* Parameters */
8af2a218 ED	130	u32 qth_min; /* Min avg length threshold: Wlog scaled */
8af2a218 ED	131	u32 qth_max; /* Max avg length threshold: Wlog scaled */
a7834745	132	u32 Scell_max;
8af2a218	133	u32 max_P; /* probability, [0 .. 1.0] 32 scaled */
809fa972 HFS	134	/* reciprocal_value(max_P / qth_delta) */
809fa972 HFS	135	struct reciprocal_value max_P_reciprocal;
8af2a218 ED	136	u32 qth_delta; /* max_th - min_th */
	137	u32 target_min; /* min_th + 0.4(max_th - min_th) /
	138	u32 target_max; /* min_th + 0.6(max_th - min_th) /
a7834745 TG	139	u8 Scell_log;
	140	u8 Wlog; /* log(W) */
	141	u8 Plog; /* random number bits */
	142	u8 Stab[RED_STAB_SIZE];
eeca6688	143	};
a7834745	144
eeca6688	145	struct red_vars {
a7834745 TG	146	/* Variables */
	147	int qcount; /* Number of packets since last random
	148	number generation */
	149	u32 qR; /* Cached random number */
	150
8af2a218	151	unsigned long qavg; /* Average queue length: Wlog scaled */
ea6a5d3b	152	ktime_t qidlestart; /* Start of current idle period */
a7834745 TG	153	};
a7834745 TG	154
8af2a218	155	static inline u32 red_maxp(u8 Plog)
a7834745	156	{
8af2a218	157	return Plog < 32 ? (~0U >> Plog) : ~0U;
a7834745 TG	158	}
a7834745 TG	159
eeca6688 ED	160	static inline void red_set_vars(struct red_vars *v)
	161	{
	162	/* Reset average queue length, the value is strictly bound
	163	* to the parameters below, reseting hurts a bit but leaving
	164	* it might result in an unreasonable qavg for a while. --TGR
	165	*/
	166	v->qavg = 0;
	167
	168	v->qcount = -1;
	169	}
8af2a218	170
bd1248f1	171	static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog, u8 Scell_log)
8afa10cb NF	172	{
	173	if (fls(qth_min) + Wlog > 32)
	174	return false;
	175	if (fls(qth_max) + Wlog > 32)
	176	return false;
bd1248f1 RD	177	if (Scell_log >= 32)
bd1248f1 RD	178	return false;
8afa10cb NF	179	if (qth_max < qth_min)
	180	return false;
	181	return true;
	182	}
	183
14bc175d PM	184	static inline int red_get_flags(unsigned char qopt_flags,
	185	unsigned char historic_mask,
	186	struct nlattr *flags_attr,
	187	unsigned char supported_mask,
	188	struct nla_bitfield32 *p_flags,
	189	unsigned char *p_userbits,
	190	struct netlink_ext_ack *extack)
	191	{
	192	struct nla_bitfield32 flags;
	193
	194	if (qopt_flags && flags_attr) {
	195	NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute");
	196	return -EINVAL;
	197	}
	198
	199	if (flags_attr) {
	200	flags = nla_get_bitfield32(flags_attr);
	201	} else {
	202	flags.selector = historic_mask;
	203	flags.value = qopt_flags & historic_mask;
	204	}
	205
	206	*p_flags = flags;
	207	*p_userbits = qopt_flags & ~historic_mask;
	208	return 0;
	209	}
	210
	211	static inline int red_validate_flags(unsigned char flags,
	212	struct netlink_ext_ack *extack)
	213	{
0a7fad23 PM	214	if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) {
	215	NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN");
	216	return -EINVAL;
	217	}
	218
14bc175d PM	219	return 0;
	220	}
	221
a7834745 TG	222	static inline void red_set_parms(struct red_parms *p,
a7834745 TG	223	u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
a73ed26b	224	u8 Scell_log, u8 *stab, u32 max_P)
a7834745	225	{
8af2a218	226	int delta = qth_max - qth_min;
a73ed26b	227	u32 max_p_delta;
8af2a218	228
a7834745 TG	229	p->qth_min = qth_min << Wlog;
	230	p->qth_max = qth_max << Wlog;
	231	p->Wlog = Wlog;
	232	p->Plog = Plog;
5c472203	233	if (delta <= 0)
8af2a218 ED	234	delta = 1;
8af2a218 ED	235	p->qth_delta = delta;
a73ed26b ED	236	if (!max_P) {
	237	max_P = red_maxp(Plog);
	238	max_P = delta; / max_P = (qth_max - qth_min)/2^Plog */
	239	}
	240	p->max_P = max_P;
	241	max_p_delta = max_P / delta;
	242	max_p_delta = max(max_p_delta, 1U);
	243	p->max_P_reciprocal = reciprocal_value(max_p_delta);
8af2a218 ED	244
	245	/* RED Adaptative target :
	246	* [min_th + 0.4*(min_th - max_th),
	247	* min_th + 0.6*(min_th - max_th)].
	248	*/
	249	delta /= 5;
	250	p->target_min = qth_min + 2*delta;
	251	p->target_max = qth_min + 3*delta;
	252
a7834745 TG	253	p->Scell_log = Scell_log;
	254	p->Scell_max = (255 << Scell_log);
	255
ddecf0f4 ED	256	if (stab)
ddecf0f4 ED	257	memcpy(p->Stab, stab, sizeof(p->Stab));
a7834745 TG	258	}
a7834745 TG	259
eeca6688	260	static inline int red_is_idling(const struct red_vars *v)
a7834745	261	{
2456e855	262	return v->qidlestart != 0;
a7834745 TG	263	}
a7834745 TG	264
eeca6688	265	static inline void red_start_of_idle_period(struct red_vars *v)
a7834745	266	{
eeca6688	267	v->qidlestart = ktime_get();
a7834745 TG	268	}
a7834745 TG	269
eeca6688	270	static inline void red_end_of_idle_period(struct red_vars *v)
a7834745	271	{
2456e855	272	v->qidlestart = 0;
a7834745 TG	273	}
a7834745 TG	274
eeca6688	275	static inline void red_restart(struct red_vars *v)
a7834745	276	{
eeca6688 ED	277	red_end_of_idle_period(v);
	278	v->qavg = 0;
	279	v->qcount = -1;
a7834745 TG	280	}
a7834745 TG	281
eeca6688 ED	282	static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
eeca6688 ED	283	const struct red_vars *v)
a7834745	284	{
eeca6688	285	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
ea6a5d3b	286	long us_idle = min_t(s64, delta, p->Scell_max);
a7834745 TG	287	int shift;
a7834745 TG	288
a7834745 TG	289	/*
	290	* The problem: ideally, average length queue recalcultion should
	291	* be done over constant clock intervals. This is too expensive, so
	292	* that the calculation is driven by outgoing packets.
	293	* When the queue is idle we have to model this clock by hand.
	294	*
	295	* SF+VJ proposed to "generate":
	296	*
	297	* m = idletime / (average_pkt_size / bandwidth)
	298	*
	299	* dummy packets as a burst after idle time, i.e.
	300	*
4362aaf6	301	* v->qavg *= (1-W)^m
a7834745 TG	302	*
	303	* This is an apparently overcomplicated solution (f.e. we have to
	304	* precompute a table to make this calculation in reasonable time)
	305	* I believe that a simpler model may be used here,
	306	* but it is field for experiments.
	307	*/
	308
	309	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
	310
	311	if (shift)
eeca6688	312	return v->qavg >> shift;
a7834745 TG	313	else {
	314	/* Approximate initial part of exponent with linear function:
	315	*
	316	* (1-W)^m ~= 1-mW + ...
	317	*
	318	* Seems, it is the best solution to
	319	* problem of too coarse exponent tabulation.
	320	*/
eeca6688	321	us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
a7834745	322
eeca6688 ED	323	if (us_idle < (v->qavg >> 1))
eeca6688 ED	324	return v->qavg - us_idle;
a7834745	325	else
eeca6688	326	return v->qavg >> 1;
a7834745 TG	327	}
	328	}
	329
8af2a218	330	static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
eeca6688	331	const struct red_vars *v,
a7834745 TG	332	unsigned int backlog)
	333	{
	334	/*
4362aaf6	335	* NOTE: v->qavg is fixed point number with point at Wlog.
a7834745 TG	336	* The formula below is equvalent to floating point
	337	* version:
	338	*
	339	* qavg = qavg(1-W) + backlogW;
	340	*
	341	* --ANK (980924)
	342	*/
eeca6688	343	return v->qavg + (backlog - (v->qavg >> p->Wlog));
a7834745 TG	344	}
a7834745 TG	345
8af2a218	346	static inline unsigned long red_calc_qavg(const struct red_parms *p,
eeca6688	347	const struct red_vars *v,
a7834745 TG	348	unsigned int backlog)
a7834745 TG	349	{
eeca6688 ED	350	if (!red_is_idling(v))
eeca6688 ED	351	return red_calc_qavg_no_idle_time(p, v, backlog);
a7834745	352	else
eeca6688	353	return red_calc_qavg_from_idle_time(p, v);
a7834745 TG	354	}
a7834745 TG	355
8af2a218 ED	356
8af2a218 ED	357	static inline u32 red_random(const struct red_parms *p)
a7834745	358	{
63862b5b	359	return reciprocal_divide(prandom_u32(), p->max_P_reciprocal);
a7834745 TG	360	}
a7834745 TG	361
eeca6688 ED	362	static inline int red_mark_probability(const struct red_parms *p,
	363	const struct red_vars *v,
	364	unsigned long qavg)
a7834745 TG	365	{
	366	/* The formula used below causes questions.
	367
8af2a218 ED	368	OK. qR is random number in the interval
8af2a218 ED	369	(0..1/max_P)*(qth_max-qth_min)
a7834745 TG	370	i.e. 0..(2^Plog). If we used floating point
	371	arithmetics, it would be: (2^Plog)*rnd_num,
	372	where rnd_num is less 1.
	373
	374	Taking into account, that qavg have fixed
8af2a218	375	point at Wlog, two lines
a7834745 TG	376	below have the following floating point equivalent:
	377
	378	max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
	379
	380	Any questions? --ANK (980924)
	381	*/
eeca6688	382	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
a7834745 TG	383	}
	384
	385	enum {
	386	RED_BELOW_MIN_THRESH,
	387	RED_BETWEEN_TRESH,
	388	RED_ABOVE_MAX_TRESH,
	389	};
	390
eeca6688	391	static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
a7834745 TG	392	{
	393	if (qavg < p->qth_min)
	394	return RED_BELOW_MIN_THRESH;
	395	else if (qavg >= p->qth_max)
	396	return RED_ABOVE_MAX_TRESH;
	397	else
	398	return RED_BETWEEN_TRESH;
	399	}
	400
	401	enum {
	402	RED_DONT_MARK,
	403	RED_PROB_MARK,
	404	RED_HARD_MARK,
	405	};
	406
eeca6688 ED	407	static inline int red_action(const struct red_parms *p,
	408	struct red_vars *v,
	409	unsigned long qavg)
a7834745 TG	410	{
	411	switch (red_cmp_thresh(p, qavg)) {
	412	case RED_BELOW_MIN_THRESH:
eeca6688	413	v->qcount = -1;
a7834745 TG	414	return RED_DONT_MARK;
	415
	416	case RED_BETWEEN_TRESH:
eeca6688 ED	417	if (++v->qcount) {
	418	if (red_mark_probability(p, v, qavg)) {
	419	v->qcount = 0;
	420	v->qR = red_random(p);
a7834745 TG	421	return RED_PROB_MARK;
	422	}
	423	} else
eeca6688	424	v->qR = red_random(p);
a7834745 TG	425
	426	return RED_DONT_MARK;
	427
	428	case RED_ABOVE_MAX_TRESH:
eeca6688	429	v->qcount = -1;
a7834745 TG	430	return RED_HARD_MARK;
	431	}
	432
	433	BUG();
	434	return RED_DONT_MARK;
	435	}
	436
eeca6688	437	static inline void red_adaptative_algo(struct red_parms p, struct red_vars v)
8af2a218 ED	438	{
	439	unsigned long qavg;
	440	u32 max_p_delta;
	441
eeca6688 ED	442	qavg = v->qavg;
	443	if (red_is_idling(v))
	444	qavg = red_calc_qavg_from_idle_time(p, v);
8af2a218	445
4362aaf6	446	/* v->qavg is fixed point number with point at Wlog */
8af2a218 ED	447	qavg >>= p->Wlog;
	448
	449	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
	450	p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
	451	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
	452	p->max_P = (p->max_P/10)9; / maxp = maxp * Beta */
	453
	454	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
a73ed26b	455	max_p_delta = max(max_p_delta, 1U);
8af2a218 ED	456	p->max_P_reciprocal = reciprocal_value(max_p_delta);
8af2a218 ED	457	}
a7834745	458	#endif