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- /* 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, u8 *stab)
- {
- 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;
- if (stab) {
- int i;
- for (i = 0; i < RED_STAB_SIZE; i++)
- if (stab[i] >= 32)
- return false;
- }
- return true;
- }
- 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
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