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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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