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

#ifndef __NET_SCHED_RED_H
#define __NET_SCHED_RED_H

#include <linux/config.h>
#include <linux/types.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>
#include <net/dsfield.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.
 */

#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 */
	u32		backlog;
};

struct red_parms
{
	/* Parameters */
	u32		qth_min;	/* Min avg length threshold: A scaled */
	u32		qth_max;	/* Max avg length threshold: A scaled */
	u32		Scell_max;
	u32		Rmask;		/* Cached random mask, see red_rmask */
	u8		Scell_log;
	u8		Wlog;		/* log(W)		*/
	u8		Plog;		/* random number bits	*/
	u8		Stab[RED_STAB_SIZE];

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

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

static inline u32 red_rmask(u8 Plog)
{
	return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;
}

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)
{
	/* 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
	 */
	p->qavg		= 0;

	p->qcount	= -1;
	p->qth_min	= qth_min << Wlog;
	p->qth_max	= qth_max << Wlog;
	p->Wlog		= Wlog;
	p->Plog		= Plog;
	p->Rmask	= red_rmask(Plog);
	p->Scell_log	= Scell_log;
	p->Scell_max	= (255 << Scell_log);

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

static inline int red_is_idling(struct red_parms *p)
{
	return !PSCHED_IS_PASTPERFECT(p->qidlestart);
}

static inline void red_start_of_idle_period(struct red_parms *p)
{
	PSCHED_GET_TIME(p->qidlestart);
}

static inline void red_end_of_idle_period(struct red_parms *p)
{
	PSCHED_SET_PASTPERFECT(p->qidlestart);
}

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

static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
{
	psched_time_t now;
	long us_idle;
	int  shift;

	PSCHED_GET_TIME(now);
	us_idle = PSCHED_TDIFF_SAFE(now, p->qidlestart, p->Scell_max);

	/*
	 * 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.
	 *
	 * 	p->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 p->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 = (p->qavg * us_idle) >> p->Scell_log;

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

static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
						       unsigned int backlog)
{
	/*
	 * NOTE: p->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 p->qavg + (backlog - (p->qavg >> p->Wlog));
}

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

static inline u32 red_random(struct red_parms *p)
{
	return net_random() & p->Rmask;
}

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

	   OK. qR is random number in the interval 0..Rmask
	   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, and Plog is related to max_P by
	   max_P = (qth_max-qth_min)/2^Plog; 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) * p->qcount < p->qR);
}

enum {
	RED_BELOW_MIN_THRESH,
	RED_BETWEEN_TRESH,
	RED_ABOVE_MAX_TRESH,
};

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

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

			return RED_DONT_MARK;

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

	BUG();
	return RED_DONT_MARK;
}

#endif
Commit	Line	Data
a7834745 TG	1	#ifndef __NET_SCHED_RED_H
	2	#define __NET_SCHED_RED_H
	3
	4	#include <linux/config.h>
	5	#include <linux/types.h>
	6	#include <net/pkt_sched.h>
	7	#include <net/inet_ecn.h>
	8	#include <net/dsfield.h>
	9
	10	/* Random Early Detection (RED) algorithm.
	11	=======================================
	12
	13	Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
	14	for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
	15
	16	This file codes a "divisionless" version of RED algorithm
	17	as written down in Fig.17 of the paper.
	18
	19	Short description.
	20	------------------
	21
	22	When a new packet arrives we calculate the average queue length:
	23
	24	avg = (1-W)avg + Wcurrent_queue_len,
	25
	26	W is the filter time constant (chosen as 2^(-Wlog)), it controls
	27	the inertia of the algorithm. To allow larger bursts, W should be
	28	decreased.
	29
	30	if (avg > th_max) -> packet marked (dropped).
	31	if (avg < th_min) -> packet passes.
	32	if (th_min < avg < th_max) we calculate probability:
	33
	34	Pb = max_P * (avg - th_min)/(th_max-th_min)
	35
	36	and mark (drop) packet with this probability.
	37	Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
	38	max_P should be small (not 1), usually 0.01..0.02 is good value.
	39
	40	max_P is chosen as a number, so that max_P/(th_max-th_min)
	41	is a negative power of two in order arithmetics to contain
	42	only shifts.
	43
	44
	45	Parameters, settable by user:
	46	-----------------------------
	47
	48	qth_min - bytes (should be < qth_max/2)
	49	qth_max - bytes (should be at least 2*qth_min and less limit)
	50	Wlog - bits (<32) log(1/W).
	51	Plog - bits (<32)
	52
	53	Plog is related to max_P by formula:
	54
	55	max_P = (qth_max-qth_min)/2^Plog;
	56
	57	F.e. if qth_max=128K and qth_min=32K, then Plog=22
	58	corresponds to max_P=0.02
	59
	60	Scell_log
	61	Stab
	62
	63	Lookup table for log((1-W)^(t/t_ave).
	64
65
66	NOTES:
67
68	Upper bound on W.
69	-----------------
70
71	If you want to allow bursts of L packets of size S,
72	you should choose W:
73
74	L + 1 - th_min/S < (1-(1-W)^L)/W
75
76	th_min/S = 32 th_min/S = 4
77
78	log(W) L
79	-1 33
80	-2 35
81	-3 39
82	-4 46
83	-5 57
84	-6 75
85	-7 101
86	-8 135
87	-9 190
88	etc.
89	*/
90
91	#define RED_STAB_SIZE 256
92	#define RED_STAB_MASK (RED_STAB_SIZE - 1)
93
94	struct red_stats
95	{
96	u32 prob_drop; /* Early probability drops */
97	u32 prob_mark; /* Early probability marks */
98	u32 forced_drop; /* Forced drops, qavg > max_thresh */
99	u32 forced_mark; /* Forced marks, qavg > max_thresh */
100	u32 pdrop; /* Drops due to queue limits */
101	u32 other; /* Drops due to drop() calls */
102	u32 backlog;
103	};
104
105	struct red_parms
106	{
107	/* Parameters */
108	u32 qth_min; /* Min avg length threshold: A scaled */
109	u32 qth_max; /* Max avg length threshold: A scaled */
110	u32 Scell_max;
111	u32 Rmask; /* Cached random mask, see red_rmask */
112	u8 Scell_log;
113	u8 Wlog; /* log(W) */
114	u8 Plog; /* random number bits */
115	u8 Stab[RED_STAB_SIZE];
116
117	/* Variables */
118	int qcount; /* Number of packets since last random
119	number generation */
120	u32 qR; /* Cached random number */
121
122	unsigned long qavg; /* Average queue length: A scaled */
123	psched_time_t qidlestart; /* Start of current idle period */
124	};
125
126	static inline u32 red_rmask(u8 Plog)
127	{
128	return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;
129	}
130
131	static inline void red_set_parms(struct red_parms *p,
132	u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
133	u8 Scell_log, u8 *stab)
134	{
135	/* Reset average queue length, the value is strictly bound
136	* to the parameters below, reseting hurts a bit but leaving
137	* it might result in an unreasonable qavg for a while. --TGR
138	*/
139	p->qavg = 0;
140
141	p->qcount = -1;
142	p->qth_min = qth_min << Wlog;
143	p->qth_max = qth_max << Wlog;
144	p->Wlog = Wlog;
145	p->Plog = Plog;
146	p->Rmask = red_rmask(Plog);
147	p->Scell_log = Scell_log;
148	p->Scell_max = (255 << Scell_log);
149
150	memcpy(p->Stab, stab, sizeof(p->Stab));
151	}
152
153	static inline int red_is_idling(struct red_parms *p)
154	{
155	return !PSCHED_IS_PASTPERFECT(p->qidlestart);
156	}
157
158	static inline void red_start_of_idle_period(struct red_parms *p)
159	{
160	PSCHED_GET_TIME(p->qidlestart);
161	}
162
163	static inline void red_end_of_idle_period(struct red_parms *p)
164	{
165	PSCHED_SET_PASTPERFECT(p->qidlestart);
166	}
167
168	static inline void red_restart(struct red_parms *p)
169	{
170	red_end_of_idle_period(p);
171	p->qavg = 0;
172	p->qcount = -1;
173	}
174
175	static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
176	{
177	psched_time_t now;
178	long us_idle;
179	int shift;
180
181	PSCHED_GET_TIME(now);
182	us_idle = PSCHED_TDIFF_SAFE(now, p->qidlestart, p->Scell_max);
183
184	/*
185	* The problem: ideally, average length queue recalcultion should
186	* be done over constant clock intervals. This is too expensive, so
187	* that the calculation is driven by outgoing packets.
188	* When the queue is idle we have to model this clock by hand.
189	*
190	* SF+VJ proposed to "generate":
191	*
192	* m = idletime / (average_pkt_size / bandwidth)
193	*
194	* dummy packets as a burst after idle time, i.e.
195	*
196	* p->qavg *= (1-W)^m
197	*
198	* This is an apparently overcomplicated solution (f.e. we have to
199	* precompute a table to make this calculation in reasonable time)
200	* I believe that a simpler model may be used here,
201	* but it is field for experiments.
202	*/
203
204	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
205
206	if (shift)
207	return p->qavg >> shift;
208	else {
209	/* Approximate initial part of exponent with linear function:
210	*
211	* (1-W)^m ~= 1-mW + ...
212	*
213	* Seems, it is the best solution to
214	* problem of too coarse exponent tabulation.
215	*/
216	us_idle = (p->qavg * us_idle) >> p->Scell_log;
217
218	if (us_idle < (p->qavg >> 1))
219	return p->qavg - us_idle;
220	else
221	return p->qavg >> 1;
222	}
223	}
224
225	static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
226	unsigned int backlog)
227	{
228	/*
229	* NOTE: p->qavg is fixed point number with point at Wlog.
230	* The formula below is equvalent to floating point
231	* version:
232	*
233	* qavg = qavg(1-W) + backlogW;
234	*
235	* --ANK (980924)
236	*/
237	return p->qavg + (backlog - (p->qavg >> p->Wlog));
238	}
239
240	static inline unsigned long red_calc_qavg(struct red_parms *p,
241	unsigned int backlog)
242	{
243	if (!red_is_idling(p))
244	return red_calc_qavg_no_idle_time(p, backlog);
245	else
246	return red_calc_qavg_from_idle_time(p);
247	}
248
249	static inline u32 red_random(struct red_parms *p)
250	{
251	return net_random() & p->Rmask;
252	}
253
254	static inline int red_mark_probability(struct red_parms *p, unsigned long qavg)
255	{
256	/* The formula used below causes questions.
257
258	OK. qR is random number in the interval 0..Rmask
259	i.e. 0..(2^Plog). If we used floating point
260	arithmetics, it would be: (2^Plog)*rnd_num,
261	where rnd_num is less 1.
262
263	Taking into account, that qavg have fixed
264	point at Wlog, and Plog is related to max_P by
265	max_P = (qth_max-qth_min)/2^Plog; two lines
266	below have the following floating point equivalent:
267
268	max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
269
270	Any questions? --ANK (980924)
271	*/
272	return !(((qavg - p->qth_min) >> p->Wlog) * p->qcount < p->qR);
273	}
274
275	enum {
276	RED_BELOW_MIN_THRESH,
277	RED_BETWEEN_TRESH,
278	RED_ABOVE_MAX_TRESH,
279	};
280
281	static inline int red_cmp_thresh(struct red_parms *p, unsigned long qavg)
282	{
283	if (qavg < p->qth_min)
284	return RED_BELOW_MIN_THRESH;
285	else if (qavg >= p->qth_max)
286	return RED_ABOVE_MAX_TRESH;
287	else
288	return RED_BETWEEN_TRESH;
289	}
290
291	enum {
292	RED_DONT_MARK,
293	RED_PROB_MARK,
294	RED_HARD_MARK,
295	};
296
297	static inline int red_action(struct red_parms *p, unsigned long qavg)
298	{
299	switch (red_cmp_thresh(p, qavg)) {
300	case RED_BELOW_MIN_THRESH:
301	p->qcount = -1;
302	return RED_DONT_MARK;
303
304	case RED_BETWEEN_TRESH:
305	if (++p->qcount) {
306	if (red_mark_probability(p, qavg)) {
307	p->qcount = 0;
308	p->qR = red_random(p);
309	return RED_PROB_MARK;
310	}
311	} else
312	p->qR = red_random(p);
313
314	return RED_DONT_MARK;
315
316	case RED_ABOVE_MAX_TRESH:
317	p->qcount = -1;
318	return RED_HARD_MARK;
319	}
320
321	BUG();
322	return RED_DONT_MARK;
323	}
324
325	#endif