#ifndef __NET_SCHED_RED_H#define __NET_SCHED_RED_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 * (u64)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