| 1 |
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| 2 | #ifndef __NET_SCHED_RED_H
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| 3 | #define __NET_SCHED_RED_H
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| 4 |
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| 5 | #include <linux/types.h>
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| 6 | #include <linux/bug.h>
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| 7 | #include <net/pkt_sched.h>
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| 8 | #include <net/inet_ecn.h>
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| 9 | #include <net/dsfield.h>
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| 10 | #include <linux/reciprocal_div.h>
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| 11 |
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| 12 | |
| 13 | =======================================
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| 14 |
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| 15 | Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
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| 16 | for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
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| 17 |
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| 18 | This file codes a "divisionless" version of RED algorithm
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| 19 | as written down in Fig.17 of the paper.
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| 20 |
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| 21 | Short description.
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| 22 | ------------------
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| 23 |
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| 24 | When a new packet arrives we calculate the average queue length:
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| 25 |
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| 26 | avg = (1-W)*avg + W*current_queue_len,
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| 27 |
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| 28 | W is the filter time constant (chosen as 2^(-Wlog)), it controls
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| 29 | the inertia of the algorithm. To allow larger bursts, W should be
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| 30 | decreased.
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| 31 |
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| 32 | if (avg > th_max) -> packet marked (dropped).
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| 33 | if (avg < th_min) -> packet passes.
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| 34 | if (th_min < avg < th_max) we calculate probability:
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| 35 |
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| 36 | Pb = max_P * (avg - th_min)/(th_max-th_min)
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| 37 |
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| 38 | and mark (drop) packet with this probability.
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| 39 | Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
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| 40 | max_P should be small (not 1), usually 0.01..0.02 is good value.
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| 41 |
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| 42 | max_P is chosen as a number, so that max_P/(th_max-th_min)
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| 43 | is a negative power of two in order arithmetic to contain
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| 44 | only shifts.
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| 45 |
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| 46 |
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| 47 | Parameters, settable by user:
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| 48 | -----------------------------
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| 49 |
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| 50 | qth_min - bytes (should be < qth_max/2)
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| 51 | qth_max - bytes (should be at least 2*qth_min and less limit)
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| 52 | Wlog - bits (<32) log(1/W).
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| 53 | Plog - bits (<32)
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| 54 |
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| 55 | Plog is related to max_P by formula:
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| 56 |
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| 57 | max_P = (qth_max-qth_min)/2^Plog;
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| 58 |
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| 59 | F.e. if qth_max=128K and qth_min=32K, then Plog=22
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| 60 | corresponds to max_P=0.02
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| 61 |
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| 62 | Scell_log
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| 63 | Stab
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| 64 |
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| 65 | Lookup table for log((1-W)^(t/t_ave).
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| 66 |
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| 67 |
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| 68 | NOTES:
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| 69 |
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| 70 | Upper bound on W.
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| 71 | -----------------
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| 72 |
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| 73 | If you want to allow bursts of L packets of size S,
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| 74 | you should choose W:
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| 75 |
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| 76 | L + 1 - th_min/S < (1-(1-W)^L)/W
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| 77 |
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| 78 | th_min/S = 32 th_min/S = 4
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| 79 |
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| 80 | log(W) L
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| 81 | -1 33
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| 82 | -2 35
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| 83 | -3 39
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| 84 | -4 46
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| 85 | -5 57
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| 86 | -6 75
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| 87 | -7 101
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| 88 | -8 135
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| 89 | -9 190
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| 90 | etc.
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| 91 |
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| 92 |
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| 93 | |
| 94 | * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
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| 95 | * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
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| 96 | *
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| 97 | * Every 500 ms:
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| 98 | * if (avg > target and max_p <= 0.5)
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| 99 | * increase max_p : max_p += alpha;
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| 100 | * else if (avg < target and max_p >= 0.01)
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| 101 | * decrease max_p : max_p *= beta;
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| 102 | *
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| 103 | * target :[qth_min + 0.4*(qth_min - qth_max),
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| 104 | * qth_min + 0.6*(qth_min - qth_max)].
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| 105 | * alpha : min(0.01, max_p / 4)
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| 106 | * beta : 0.9
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| 107 | * max_P is a Q0.32 fixed point number (with 32 bits mantissa)
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| 108 | * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
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| 109 |
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| 110 | #define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))
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| 111 |
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| 112 | #define MAX_P_MIN (1 * RED_ONE_PERCENT)
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| 113 | #define MAX_P_MAX (50 * RED_ONE_PERCENT)
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| 114 | #define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)
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| 115 |
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| 116 | #define RED_STAB_SIZE 256
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| 117 | #define RED_STAB_MASK (RED_STAB_SIZE - 1)
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| 118 |
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| 119 | struct red_stats {
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| 120 | u32 prob_drop;
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| 121 | u32 prob_mark;
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| 122 | u32 forced_drop;
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| 123 | u32 forced_mark;
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| 124 | u32 pdrop;
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| 125 | };
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| 126 |
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| 127 | struct red_parms {
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| 128 |
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| 129 | u32 qth_min;
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| 130 | u32 qth_max;
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| 131 | u32 Scell_max;
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| 132 | u32 max_P;
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| 133 |
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| 134 | struct reciprocal_value max_P_reciprocal;
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| 135 | u32 qth_delta;
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| 136 | u32 target_min;
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| 137 | u32 target_max;
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| 138 | u8 Scell_log;
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| 139 | u8 Wlog;
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| 140 | u8 Plog;
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| 141 | u8 Stab[RED_STAB_SIZE];
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| 142 | };
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| 143 |
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| 144 | struct red_vars {
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| 145 |
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| 146 | int qcount; |
| 147 | number generation
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| 148 | u32 qR;
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| 149 |
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| 150 | unsigned long qavg;
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| 151 | ktime_t qidlestart;
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| 152 | };
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| 153 |
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| 154 | static inline u32 red_maxp(u8 Plog)
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| 155 | {
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| 156 | return Plog < 32 ? (~0U >> Plog) : ~0U;
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| 157 | }
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| 158 |
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| 159 | static inline void red_set_vars(struct red_vars *v)
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| 160 | {
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| 161 | |
| 162 | * to the parameters below, resetting hurts a bit but leaving
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| 163 | * it might result in an unreasonable qavg for a while. --TGR
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| 164 |
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| 165 | v->qavg = 0;
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| 166 |
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| 167 | v->qcount = -1;
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| 168 | }
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| 169 |
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| 170 | static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog,
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| 171 | u8 Scell_log, u8 *stab)
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| 172 | {
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| 173 | if (fls(qth_min) + Wlog >= 32)
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| 174 | return false;
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| 175 | if (fls(qth_max) + Wlog >= 32)
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| 176 | return false;
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| 177 | if (Scell_log >= 32)
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| 178 | return false;
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| 179 | if (qth_max < qth_min)
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| 180 | return false;
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| 181 | if (stab) {
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| 182 | int i;
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| 183 |
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| 184 | for (i = 0; i < RED_STAB_SIZE; i++)
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| 185 | if (stab[i] >= 32)
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| 186 | return false;
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| 187 | }
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| 188 | return true;
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| 189 | }
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| 190 |
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| 191 | static inline int red_get_flags(unsigned char qopt_flags,
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| 192 | unsigned char historic_mask,
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| 193 | struct nlattr *flags_attr,
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| 194 | unsigned char supported_mask,
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| 195 | struct nla_bitfield32 *p_flags,
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| 196 | unsigned char *p_userbits,
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| 197 | struct netlink_ext_ack *extack)
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| 198 | {
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| 199 | struct nla_bitfield32 flags;
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| 200 |
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| 201 | if (qopt_flags && flags_attr) {
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| 202 | NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute");
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| 203 | return -EINVAL;
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| 204 | }
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| 205 |
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| 206 | if (flags_attr) {
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| 207 | flags = nla_get_bitfield32(flags_attr);
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| 208 | } else {
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| 209 | flags.selector = historic_mask;
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| 210 | flags.value = qopt_flags & historic_mask;
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| 211 | }
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| 212 |
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| 213 | *p_flags = flags;
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| 214 | *p_userbits = qopt_flags & ~historic_mask;
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| 215 | return 0;
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| 216 | }
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| 217 |
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| 218 | static inline int red_validate_flags(unsigned char flags,
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| 219 | struct netlink_ext_ack *extack)
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| 220 | {
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| 221 | if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) {
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| 222 | NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN");
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| 223 | return -EINVAL;
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| 224 | }
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| 225 |
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| 226 | return 0;
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| 227 | }
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| 228 |
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| 229 | static inline void red_set_parms(struct red_parms *p,
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| 230 | u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
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| 231 | u8 Scell_log, u8 *stab, u32 max_P)
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| 232 | {
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| 233 | int delta = qth_max - qth_min;
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| 234 | u32 max_p_delta;
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| 235 |
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| 236 | WRITE_ONCE(p->qth_min, qth_min << Wlog);
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| 237 | WRITE_ONCE(p->qth_max, qth_max << Wlog);
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| 238 | WRITE_ONCE(p->Wlog, Wlog);
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| 239 | WRITE_ONCE(p->Plog, Plog);
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| 240 | if (delta <= 0)
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| 241 | delta = 1;
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| 242 | p->qth_delta = delta;
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| 243 | if (!max_P) {
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| 244 | max_P = red_maxp(Plog);
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| 245 | max_P *= delta;
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| 246 | }
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| 247 | WRITE_ONCE(p->max_P, max_P);
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| 248 | max_p_delta = max_P / delta;
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| 249 | max_p_delta = max(max_p_delta, 1U);
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| 250 | p->max_P_reciprocal = reciprocal_value(max_p_delta);
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| 251 |
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| 252 | |
| 253 | * [min_th + 0.4*(min_th - max_th),
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| 254 | * min_th + 0.6*(min_th - max_th)].
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| 255 |
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| 256 | delta /= 5;
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| 257 | p->target_min = qth_min + 2*delta;
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| 258 | p->target_max = qth_min + 3*delta;
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| 259 |
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| 260 | WRITE_ONCE(p->Scell_log, Scell_log);
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| 261 | p->Scell_max = (255 << Scell_log);
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| 262 |
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| 263 | if (stab)
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| 264 | memcpy(p->Stab, stab, sizeof(p->Stab));
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| 265 | }
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| 266 |
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| 267 | static inline int red_is_idling(const struct red_vars *v)
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| 268 | {
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| 269 | return v->qidlestart != 0;
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| 270 | }
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| 271 |
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| 272 | static inline void red_start_of_idle_period(struct red_vars *v)
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| 273 | {
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| 274 | v->qidlestart = ktime_get();
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| 275 | }
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| 276 |
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| 277 | static inline void red_end_of_idle_period(struct red_vars *v)
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| 278 | {
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| 279 | v->qidlestart = 0;
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| 280 | }
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| 281 |
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| 282 | static inline void red_restart(struct red_vars *v)
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| 283 | {
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| 284 | red_end_of_idle_period(v);
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| 285 | v->qavg = 0;
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| 286 | v->qcount = -1;
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| 287 | }
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| 288 |
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| 289 | static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
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| 290 | const struct red_vars *v)
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| 291 | {
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| 292 | s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
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| 293 | long us_idle = min_t(s64, delta, p->Scell_max);
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| 294 | int shift;
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| 295 |
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| 296 | |
| 297 | * The problem: ideally, average length queue recalculation should
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| 298 | * be done over constant clock intervals. This is too expensive, so
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| 299 | * that the calculation is driven by outgoing packets.
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| 300 | * When the queue is idle we have to model this clock by hand.
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| 301 | *
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| 302 | * SF+VJ proposed to "generate":
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| 303 | *
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| 304 | * m = idletime / (average_pkt_size / bandwidth)
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| 305 | *
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| 306 | * dummy packets as a burst after idle time, i.e.
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| 307 | *
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| 308 | * v->qavg *= (1-W)^m
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| 309 | *
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| 310 | * This is an apparently overcomplicated solution (f.e. we have to
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| 311 | * precompute a table to make this calculation in reasonable time)
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| 312 | * I believe that a simpler model may be used here,
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| 313 | * but it is field for experiments.
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| 314 |
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| 315 |
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| 316 | shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
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| 317 |
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| 318 | if (shift)
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| 319 | return v->qavg >> shift;
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| 320 | else {
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| 321 | |
| 322 | *
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| 323 | * (1-W)^m ~= 1-mW + ...
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| 324 | *
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| 325 | * Seems, it is the best solution to
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| 326 | * problem of too coarse exponent tabulation.
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| 327 |
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| 328 | us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
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| 329 |
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| 330 | if (us_idle < (v->qavg >> 1))
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| 331 | return v->qavg - us_idle;
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| 332 | else
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| 333 | return v->qavg >> 1;
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| 334 | }
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| 335 | }
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| 336 |
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| 337 | static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
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| 338 | const struct red_vars *v,
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| 339 | unsigned int backlog)
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| 340 | {
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| 341 | |
| 342 | * NOTE: v->qavg is fixed point number with point at Wlog.
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| 343 | * The formula below is equivalent to floating point
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| 344 | * version:
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| 345 | *
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| 346 | * qavg = qavg*(1-W) + backlog*W;
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| 347 | *
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| 348 | * --ANK (980924)
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| 349 |
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| 350 | return v->qavg + (backlog - (v->qavg >> p->Wlog));
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| 351 | }
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| 352 |
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| 353 | static inline unsigned long red_calc_qavg(const struct red_parms *p,
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| 354 | const struct red_vars *v,
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| 355 | unsigned int backlog)
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| 356 | {
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| 357 | if (!red_is_idling(v))
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| 358 | return red_calc_qavg_no_idle_time(p, v, backlog);
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| 359 | else
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| 360 | return red_calc_qavg_from_idle_time(p, v);
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| 361 | }
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| 362 |
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| 363 |
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| 364 | static inline u32 red_random(const struct red_parms *p)
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| 365 | {
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| 366 | return reciprocal_divide(get_random_u32(), p->max_P_reciprocal);
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| 367 | }
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| 368 |
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| 369 | static inline int red_mark_probability(const struct red_parms *p,
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| 370 | const struct red_vars *v,
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| 371 | unsigned long qavg)
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| 372 | {
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| 373 | |
| 374 |
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| 375 | OK. qR is random number in the interval
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| 376 | (0..1/max_P)*(qth_max-qth_min)
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| 377 | i.e. 0..(2^Plog). If we used floating point
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| 378 | arithmetic, it would be: (2^Plog)*rnd_num,
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| 379 | where rnd_num is less 1.
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| 380 |
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| 381 | Taking into account, that qavg have fixed
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| 382 | point at Wlog, two lines
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| 383 | below have the following floating point equivalent:
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| 384 |
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| 385 | max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
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| 386 |
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| 387 | Any questions? --ANK (980924)
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| 388 |
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| 389 | return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
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| 390 | }
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| 391 |
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| 392 | enum {
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| 393 | RED_BELOW_MIN_THRESH,
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| 394 | RED_BETWEEN_TRESH,
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| 395 | RED_ABOVE_MAX_TRESH,
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| 396 | };
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| 397 |
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| 398 | static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
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| 399 | {
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| 400 | if (qavg < p->qth_min)
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| 401 | return RED_BELOW_MIN_THRESH;
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| 402 | else if (qavg >= p->qth_max)
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| 403 | return RED_ABOVE_MAX_TRESH;
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| 404 | else
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| 405 | return RED_BETWEEN_TRESH;
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| 406 | }
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| 407 |
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| 408 | enum {
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| 409 | RED_DONT_MARK,
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| 410 | RED_PROB_MARK,
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| 411 | RED_HARD_MARK,
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| 412 | };
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| 413 |
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| 414 | static inline int red_action(const struct red_parms *p,
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| 415 | struct red_vars *v,
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| 416 | unsigned long qavg)
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| 417 | {
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| 418 | switch (red_cmp_thresh(p, qavg)) {
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| 419 | case RED_BELOW_MIN_THRESH:
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| 420 | v->qcount = -1;
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| 421 | return RED_DONT_MARK;
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| 422 |
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| 423 | case RED_BETWEEN_TRESH:
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| 424 | if (++v->qcount) {
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| 425 | if (red_mark_probability(p, v, qavg)) {
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| 426 | v->qcount = 0;
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| 427 | v->qR = red_random(p);
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| 428 | return RED_PROB_MARK;
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| 429 | }
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| 430 | } else
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| 431 | v->qR = red_random(p);
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| 432 |
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| 433 | return RED_DONT_MARK;
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| 434 |
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| 435 | case RED_ABOVE_MAX_TRESH:
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| 436 | v->qcount = -1;
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| 437 | return RED_HARD_MARK;
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| 438 | }
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| 439 |
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| 440 | BUG();
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| 441 | return RED_DONT_MARK;
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| 442 | }
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| 443 |
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| 444 | static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
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| 445 | {
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| 446 | unsigned long qavg;
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| 447 | u32 max_p_delta;
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| 448 |
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| 449 | qavg = v->qavg;
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| 450 | if (red_is_idling(v))
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| 451 | qavg = red_calc_qavg_from_idle_time(p, v);
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| 452 |
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| 453 |
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| 454 | qavg >>= p->Wlog;
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| 455 |
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| 456 | if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
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| 457 | p->max_P += MAX_P_ALPHA(p->max_P);
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| 458 | else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
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| 459 | p->max_P = (p->max_P/10)*9;
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| 460 |
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| 461 | max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
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| 462 | max_p_delta = max(max_p_delta, 1U);
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| 463 | p->max_P_reciprocal = reciprocal_value(max_p_delta);
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| 464 | }
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| 465 | #endif
|