cregit-Linux how code gets into the kernel

Release 4.12 include/net/red.h

Directory: include/net
#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; }

Contributors

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Thomas Graf2080.00%150.00%
Eric Dumazet520.00%150.00%
Total25100.00%2100.00%


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; }

Contributors

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Eric Dumazet26100.00%1100.00%
Total26100.00%1100.00%


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)); }

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PersonTokensPropCommitsCommitProp
Eric Dumazet10050.51%375.00%
Thomas Graf9849.49%125.00%
Total198100.00%4100.00%


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

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PersonTokensPropCommitsCommitProp
Thomas Graf1470.00%120.00%
Eric Dumazet525.00%360.00%
Patrick McHardy15.00%120.00%
Total20100.00%5100.00%


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

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Thomas Graf1368.42%125.00%
Eric Dumazet421.05%250.00%
Patrick McHardy210.53%125.00%
Total19100.00%4100.00%


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

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Thomas Graf1372.22%125.00%
Eric Dumazet422.22%250.00%
Patrick McHardy15.56%125.00%
Total18100.00%4100.00%


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

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Thomas Graf2583.33%150.00%
Eric Dumazet516.67%150.00%
Total30100.00%2100.00%


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; } }

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PersonTokensPropCommitsCommitProp
Thomas Graf9070.87%116.67%
Eric Dumazet3325.98%350.00%
Ilpo Järvinen32.36%116.67%
David Ward10.79%116.67%
Total127100.00%6100.00%


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)); }

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PersonTokensPropCommitsCommitProp
Thomas Graf3477.27%125.00%
Eric Dumazet920.45%250.00%
David Ward12.27%125.00%
Total44100.00%4100.00%


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); }

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Thomas Graf3976.47%133.33%
Eric Dumazet1223.53%266.67%
Total51100.00%3100.00%


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

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PersonTokensPropCommitsCommitProp
Thomas Graf1770.83%133.33%
Eric Dumazet625.00%133.33%
Aruna-Hewapathirane14.17%133.33%
Total24100.00%3100.00%


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); }

Contributors

PersonTokensPropCommitsCommitProp
Thomas Graf4080.00%133.33%
Eric Dumazet1020.00%266.67%
Total50100.00%3100.00%

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; }

Contributors

PersonTokensPropCommitsCommitProp
Thomas Graf4397.73%150.00%
Eric Dumazet12.27%150.00%
Total44100.00%2100.00%

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; }

Contributors

PersonTokensPropCommitsCommitProp
Thomas Graf10788.43%150.00%
Eric Dumazet1411.57%150.00%
Total121100.00%2100.00%


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); }

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Eric Dumazet13999.29%375.00%
David Ward10.71%125.00%
Total140100.00%4100.00%

#endif

Overall Contributors

PersonTokensPropCommitsCommitProp
Thomas Graf67960.79%17.69%
Eric Dumazet42137.69%538.46%
Patrick McHardy40.36%215.38%
Ilpo Järvinen30.27%17.69%
Hannes Frederic Sowa30.27%17.69%
David Ward30.27%17.69%
Paul Gortmaker30.27%17.69%
Aruna-Hewapathirane10.09%17.69%
Total1117100.00%13100.00%
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