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 /* * Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand. * Copyright (c) 2005 Ian McDonald * Copyright (c) 2005 Arnaldo Carvalho de Melo * Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. */ #include #include "../../dccp.h" #include "tfrc.h" #define TFRC_CALC_X_ARRSIZE 500 #define TFRC_CALC_X_SPLIT 50000 /* 0.05 * 1000000, details below */ #define TFRC_SMALLEST_P (TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE) /* TFRC TCP Reno Throughput Equation Lookup Table for f(p) The following two-column lookup table implements a part of the TCP throughput equation from [RFC 3448, sec. 3.1]: s X_calc = -------------------------------------------------------------- R * sqrt(2*b*p/3) + (3 * t_RTO * sqrt(3*b*p/8) * (p + 32*p^3)) Where: X is the transmit rate in bytes/second s is the packet size in bytes R is the round trip time in seconds p is the loss event rate, between 0 and 1.0, of the number of loss events as a fraction of the number of packets transmitted t_RTO is the TCP retransmission timeout value in seconds b is the number of packets acknowledged by a single TCP ACK We can assume that b = 1 and t_RTO is 4 * R. The equation now becomes: s X_calc = ------------------------------------------------------- R * sqrt(p*2/3) + (12 * R * sqrt(p*3/8) * (p + 32*p^3)) which we can break down into: s X_calc = --------- R * f(p) where f(p) is given for 0 < p <= 1 by: f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (p + 32*p^3) Since this is kernel code, floating-point arithmetic is avoided in favour of integer arithmetic. This means that nearly all fractional parameters are scaled by 1000000: * the parameters p and R * the return result f(p) The lookup table therefore actually tabulates the following function g(q): g(q) = 1000000 * f(q/1000000) Hence, when p <= 1, q must be less than or equal to 1000000. To achieve finer granularity for the practically more relevant case of small values of p (up to 5%), the second column is used; the first one ranges up to 100%. This split corresponds to the value of q = TFRC_CALC_X_SPLIT. At the same time this also determines the smallest resolution possible with this lookup table: TFRC_SMALLEST_P = TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE The entire table is generated by: for(i=0; i < TFRC_CALC_X_ARRSIZE; i++) { lookup[i][0] = g((i+1) * 1000000/TFRC_CALC_X_ARRSIZE); lookup[i][1] = g((i+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE); } With the given configuration, we have, with M = TFRC_CALC_X_ARRSIZE-1, lookup[0][0] = g(1000000/(M+1)) = 1000000 * f(0.2%) lookup[M][0] = g(1000000) = 1000000 * f(100%) lookup[0][1] = g(TFRC_SMALLEST_P) = 1000000 * f(0.01%) lookup[M][1] = g(TFRC_CALC_X_SPLIT) = 1000000 * f(5%) In summary, the two columns represent f(p) for the following ranges: * The first column is for 0.002 <= p <= 1.0 * The second column is for 0.0001 <= p <= 0.05 Where the columns overlap, the second (finer-grained) is given preference, i.e. the first column is used only for p >= 0.05. */ static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = { { 37172, 8172 }, { 53499, 11567 }, { 66664, 14180 }, { 78298, 16388 }, { 89021, 18339 }, { 99147, 20108 }, { 108858, 21738 }, { 118273, 23260 }, { 127474, 24693 }, { 136520, 26052 }, { 145456, 27348 }, { 154316, 28589 }, { 163130, 29783 }, { 171919, 30935 }, { 180704, 32049 }, { 189502, 33130 }, { 198328, 34180 }, { 207194, 35202 }, { 216114, 36198 }, { 225097, 37172 }, { 234153, 38123 }, { 243294, 39055 }, { 252527, 39968 }, { 261861, 40864 }, { 271305, 41743 }, { 280866, 42607 }, { 290553, 43457 }, { 300372, 44293 }, { 310333, 45117 }, { 320441, 45929 }, { 330705, 46729 }, { 341131, 47518 }, { 351728, 48297 }, { 362501, 49066 }, { 373460, 49826 }, { 384609, 50577 }, { 395958, 51320 }, { 407513, 52054 }, { 419281, 52780 }, { 431270, 53499 }, { 443487, 54211 }, { 455940, 54916 }, { 468635, 55614 }, { 481581, 56306 }, { 494785, 56991 }, { 508254, 57671 }, { 521996, 58345 }, { 536019, 59014 }, { 550331, 59677 }, { 564939, 60335 }, { 579851, 60988 }, { 595075, 61636 }, { 610619, 62279 }, { 626491, 62918 }, { 642700, 63553 }, { 659253, 64183 }, { 676158, 64809 }, { 693424, 65431 }, { 711060, 66050 }, { 729073, 66664 }, { 747472, 67275 }, { 766266, 67882 }, { 785464, 68486 }, { 805073, 69087 }, { 825103, 69684 }, { 845562, 70278 }, { 866460, 70868 }, { 887805, 71456 }, { 909606, 72041 }, { 931873, 72623 }, { 954614, 73202 }, { 977839, 73778 }, { 1001557, 74352 }, { 1025777, 74923 }, { 1050508, 75492 }, { 1075761, 76058 }, { 1101544, 76621 }, { 1127867, 77183 }, { 1154739, 77741 }, { 1182172, 78298 }, { 1210173, 78852 }, { 1238753, 79405 }, { 1267922, 79955 }, { 1297689, 80503 }, { 1328066, 81049 }, { 1359060, 81593 }, { 1390684, 82135 }, { 1422947, 82675 }, { 1455859, 83213 }, { 1489430, 83750 }, { 1523671, 84284 }, { 1558593, 84817 }, { 1594205, 85348 }, { 1630518, 85878 }, { 1667543, 86406 }, { 1705290, 86932 }, { 1743770, 87457 }, { 1782994, 87980 }, { 1822973, 88501 }, { 1863717, 89021 }, { 1905237, 89540 }, { 1947545, 90057 }, { 1990650, 90573 }, { 2034566, 91087 }, { 2079301, 91600 }, { 2124869, 92111 }, { 2171279, 92622 }, { 2218543, 93131 }, { 2266673, 93639 }, { 2315680, 94145 }, { 2365575, 94650 }, { 2416371, 95154 }, { 2468077, 95657 }, { 2520707, 96159 }, { 2574271, 96660 }, { 2628782, 97159 }, { 2684250, 97658 }, { 2740689, 98155 }, { 2798110, 98651 }, { 2856524, 99147 }, { 2915944, 99641 }, { 2976382, 100134 }, { 3037850, 100626 }, { 3100360, 101117 }, { 3163924, 101608 }, { 3228554, 102097 }, { 3294263, 102586 }, { 3361063, 103073 }, { 3428966, 103560 }, { 3497984, 104045 }, { 3568131, 104530 }, { 3639419, 105014 }, { 3711860, 105498 }, { 3785467, 105980 }, { 3860253, 106462 }, { 3936229, 106942 }, { 4013410, 107422 }, { 4091808, 107902 }, { 4171435, 108380 }, { 4252306, 108858 }, { 4334431, 109335 }, { 4417825, 109811 }, { 4502501, 110287 }, { 4588472, 110762 }, { 4675750, 111236 }, { 4764349, 111709 }, { 4854283, 112182 }, { 4945564, 112654 }, { 5038206, 113126 }, { 5132223, 113597 }, { 5227627, 114067 }, { 5324432, 114537 }, { 5422652, 115006 }, { 5522299, 115474 }, { 5623389, 115942 }, { 5725934, 116409 }, { 5829948, 116876 }, { 5935446, 117342 }, { 6042439, 117808 }, { 6150943, 118273 }, { 6260972, 118738 }, { 6372538, 119202 }, { 6485657, 119665 }, { 6600342, 120128 }, { 6716607, 120591 }, { 6834467, 121053 }, { 6953935, 121514 }, { 7075025, 121976 }, { 7197752, 122436 }, { 7322131, 122896 }, { 7448175, 123356 }, { 7575898, 123815 }, { 7705316, 124274 }, { 7836442, 124733 }, { 7969291, 125191 }, { 8103877, 125648 }, { 8240216, 126105 }, { 8378321, 126562 }, { 8518208, 127018 }, { 8659890, 127474 }, { 8803384, 127930 }, { 8948702, 128385 }, { 9095861, 128840 }, { 9244875, 129294 }, { 9395760, 129748 }, { 9548529, 130202 }, { 9703198, 130655 }, { 9859782, 131108 }, { 10018296, 131561 }, { 10178755, 132014 }, { 10341174, 132466 }, { 10505569, 132917 }, { 10671954, 133369 }, { 10840345, 133820 }, { 11010757, 134271 }, { 11183206, 134721 }, { 11357706, 135171 }, { 11534274, 135621 }, { 11712924, 136071 }, { 11893673, 136520 }, { 12076536, 136969 }, { 12261527, 137418 }, { 12448664, 137867 }, { 12637961, 138315 }, { 12829435, 138763 }, { 13023101, 139211 }, { 13218974, 139658 }, { 13417071, 140106 }, { 13617407, 140553 }, { 13819999, 140999 }, { 14024862, 141446 }, { 14232012, 141892 }, { 14441465, 142339 }, { 14653238, 142785 }, { 14867346, 143230 }, { 15083805, 143676 }, { 15302632, 144121 }, { 15523842, 144566 }, { 15747453, 145011 }, { 15973479, 145456 }, { 16201939, 145900 }, { 16432847, 146345 }, { 16666221, 146789 }, { 16902076, 147233 }, { 17140429, 147677 }, { 17381297, 148121 }, { 17624696, 148564 }, { 17870643, 149007 }, { 18119154, 149451 }, { 18370247, 149894 }, { 18623936, 150336 }, { 18880241, 150779 }, { 19139176, 151222 }, { 19400759, 151664 }, { 19665007, 152107 }, { 19931936, 152549 }, { 20201564, 152991 }, { 20473907, 153433 }, { 20748982, 153875 }, { 21026807, 154316 }, { 21307399, 154758 }, { 21590773, 155199 }, { 21876949, 155641 }, { 22165941, 156082 }, { 22457769, 156523 }, { 22752449, 156964 }, { 23049999, 157405 }, { 23350435, 157846 }, { 23653774, 158287 }, { 23960036, 158727 }, { 24269236, 159168 }, { 24581392, 159608 }, { 24896521, 160049 }, { 25214642, 160489 }, { 25535772, 160929 }, { 25859927, 161370 }, { 26187127, 161810 }, { 26517388, 162250 }, { 26850728, 162690 }, { 27187165, 163130 }, { 27526716, 163569 }, { 27869400, 164009 }, { 28215234, 164449 }, { 28564236, 164889 }, { 28916423, 165328 }, { 29271815, 165768 }, { 29630428, 166208 }, { 29992281, 166647 }, { 30357392, 167087 }, { 30725779, 167526 }, { 31097459, 167965 }, { 31472452, 168405 }, { 31850774, 168844 }, { 32232445, 169283 }, { 32617482, 169723 }, { 33005904, 170162 }, { 33397730, 170601 }, { 33792976, 171041 }, { 34191663, 171480 }, { 34593807, 171919 }, { 34999428, 172358 }, { 35408544, 172797 }, { 35821174, 173237 }, { 36237335, 173676 }, { 36657047, 174115 }, { 37080329, 174554 }, { 37507197, 174993 }, { 37937673, 175433 }, { 38371773, 175872 }, { 38809517, 176311 }, { 39250924, 176750 }, { 39696012, 177190 }, { 40144800, 177629 }, { 40597308, 178068 }, { 41053553, 178507 }, { 41513554, 178947 }, { 41977332, 179386 }, { 42444904, 179825 }, { 42916290, 180265 }, { 43391509, 180704 }, { 43870579, 181144 }, { 44353520, 181583 }, { 44840352, 182023 }, { 45331092, 182462 }, { 45825761, 182902 }, { 46324378, 183342 }, { 46826961, 183781 }, { 47333531, 184221 }, { 47844106, 184661 }, { 48358706, 185101 }, { 48877350, 185541 }, { 49400058, 185981 }, { 49926849, 186421 }, { 50457743, 186861 }, { 50992759, 187301 }, { 51531916, 187741 }, { 52075235, 188181 }, { 52622735, 188622 }, { 53174435, 189062 }, { 53730355, 189502 }, { 54290515, 189943 }, { 54854935, 190383 }, { 55423634, 190824 }, { 55996633, 191265 }, { 56573950, 191706 }, { 57155606, 192146 }, { 57741621, 192587 }, { 58332014, 193028 }, { 58926806, 193470 }, { 59526017, 193911 }, { 60129666, 194352 }, { 60737774, 194793 }, { 61350361, 195235 }, { 61967446, 195677 }, { 62589050, 196118 }, { 63215194, 196560 }, { 63845897, 197002 }, { 64481179, 197444 }, { 65121061, 197886 }, { 65765563, 198328 }, { 66414705, 198770 }, { 67068508, 199213 }, { 67726992, 199655 }, { 68390177, 200098 }, { 69058085, 200540 }, { 69730735, 200983 }, { 70408147, 201426 }, { 71090343, 201869 }, { 71777343, 202312 }, { 72469168, 202755 }, { 73165837, 203199 }, { 73867373, 203642 }, { 74573795, 204086 }, { 75285124, 204529 }, { 76001380, 204973 }, { 76722586, 205417 }, { 77448761, 205861 }, { 78179926, 206306 }, { 78916102, 206750 }, { 79657310, 207194 }, { 80403571, 207639 }, { 81154906, 208084 }, { 81911335, 208529 }, { 82672880, 208974 }, { 83439562, 209419 }, { 84211402, 209864 }, { 84988421, 210309 }, { 85770640, 210755 }, { 86558080, 211201 }, { 87350762, 211647 }, { 88148708, 212093 }, { 88951938, 212539 }, { 89760475, 212985 }, { 90574339, 213432 }, { 91393551, 213878 }, { 92218133, 214325 }, { 93048107, 214772 }, { 93883493, 215219 }, { 94724314, 215666 }, { 95570590, 216114 }, { 96422343, 216561 }, { 97279594, 217009 }, { 98142366, 217457 }, { 99010679, 217905 }, { 99884556, 218353 }, { 100764018, 218801 }, { 101649086, 219250 }, { 102539782, 219698 }, { 103436128, 220147 }, { 104338146, 220596 }, { 105245857, 221046 }, { 106159284, 221495 }, { 107078448, 221945 }, { 108003370, 222394 }, { 108934074, 222844 }, { 109870580, 223294 }, { 110812910, 223745 }, { 111761087, 224195 }, { 112715133, 224646 }, { 113675069, 225097 }, { 114640918, 225548 }, { 115612702, 225999 }, { 116590442, 226450 }, { 117574162, 226902 }, { 118563882, 227353 }, { 119559626, 227805 }, { 120561415, 228258 }, { 121569272, 228710 }, { 122583219, 229162 }, { 123603278, 229615 }, { 124629471, 230068 }, { 125661822, 230521 }, { 126700352, 230974 }, { 127745083, 231428 }, { 128796039, 231882 }, { 129853241, 232336 }, { 130916713, 232790 }, { 131986475, 233244 }, { 133062553, 233699 }, { 134144966, 234153 }, { 135233739, 234608 }, { 136328894, 235064 }, { 137430453, 235519 }, { 138538440, 235975 }, { 139652876, 236430 }, { 140773786, 236886 }, { 141901190, 237343 }, { 143035113, 237799 }, { 144175576, 238256 }, { 145322604, 238713 }, { 146476218, 239170 }, { 147636442, 239627 }, { 148803298, 240085 }, { 149976809, 240542 }, { 151156999, 241000 }, { 152343890, 241459 }, { 153537506, 241917 }, { 154737869, 242376 }, { 155945002, 242835 }, { 157158929, 243294 }, { 158379673, 243753 }, { 159607257, 244213 }, { 160841704, 244673 }, { 162083037, 245133 }, { 163331279, 245593 }, { 164586455, 246054 }, { 165848586, 246514 }, { 167117696, 246975 }, { 168393810, 247437 }, { 169676949, 247898 }, { 170967138, 248360 }, { 172264399, 248822 }, { 173568757, 249284 }, { 174880235, 249747 }, { 176198856, 250209 }, { 177524643, 250672 }, { 178857621, 251136 }, { 180197813, 251599 }, { 181545242, 252063 }, { 182899933, 252527 }, { 184261908, 252991 }, { 185631191, 253456 }, { 187007807, 253920 }, { 188391778, 254385 }, { 189783129, 254851 }, { 191181884, 255316 }, { 192588065, 255782 }, { 194001698, 256248 }, { 195422805, 256714 }, { 196851411, 257181 }, { 198287540, 257648 }, { 199731215, 258115 }, { 201182461, 258582 }, { 202641302, 259050 }, { 204107760, 259518 }, { 205581862, 259986 }, { 207063630, 260454 }, { 208553088, 260923 }, { 210050262, 261392 }, { 211555174, 261861 }, { 213067849, 262331 }, { 214588312, 262800 }, { 216116586, 263270 }, { 217652696, 263741 }, { 219196666, 264211 }, { 220748520, 264682 }, { 222308282, 265153 }, { 223875978, 265625 }, { 225451630, 266097 }, { 227035265, 266569 }, { 228626905, 267041 }, { 230226576, 267514 }, { 231834302, 267986 }, { 233450107, 268460 }, { 235074016, 268933 }, { 236706054, 269407 }, { 238346244, 269881 }, { 239994613, 270355 }, { 241651183, 270830 }, { 243315981, 271305 } }; /* return largest index i such that fval <= lookup[i][small] */ static inline u32 tfrc_binsearch(u32 fval, u8 small) { u32 try, low = 0, high = TFRC_CALC_X_ARRSIZE - 1; while (low < high) { try = (low + high) / 2; if (fval <= tfrc_calc_x_lookup[try][small]) high = try; else low = try + 1; } return high; } /** * tfrc_calc_x - Calculate the send rate as per section 3.1 of RFC3448 * @s: packet size in bytes * @R: RTT scaled by 1000000 (i.e., microseconds) * @p: loss ratio estimate scaled by 1000000 * * Returns X_calc in bytes per second (not scaled). */ u32 tfrc_calc_x(u16 s, u32 R, u32 p) { u16 index; u32 f; u64 result; /* check against invalid parameters and divide-by-zero */ BUG_ON(p > 1000000); /* p must not exceed 100% */ BUG_ON(p == 0); /* f(0) = 0, divide by zero */ if (R == 0) { /* possible divide by zero */ DCCP_CRIT("WARNING: RTT is 0, returning maximum X_calc."); return ~0U; } if (p <= TFRC_CALC_X_SPLIT) { /* 0.0000 < p <= 0.05 */ if (p < TFRC_SMALLEST_P) { /* 0.0000 < p < 0.0001 */ DCCP_WARN("Value of p (%d) below resolution. " "Substituting %d\n", p, TFRC_SMALLEST_P); index = 0; } else /* 0.0001 <= p <= 0.05 */ index = p/TFRC_SMALLEST_P - 1; f = tfrc_calc_x_lookup[index][1]; } else { /* 0.05 < p <= 1.00 */ index = p/(1000000/TFRC_CALC_X_ARRSIZE) - 1; f = tfrc_calc_x_lookup[index][0]; } /* * Compute X = s/(R*f(p)) in bytes per second. * Since f(p) and R are both scaled by 1000000, we need to multiply by * 1000000^2. To avoid overflow, the result is computed in two stages. * This works under almost all reasonable operational conditions, for a * wide range of parameters. Yet, should some strange combination of * parameters result in overflow, the use of scaled_div32 will catch * this and return UINT_MAX - which is a logically adequate consequence. */ result = scaled_div(s, R); return scaled_div32(result, f); } /** * tfrc_calc_x_reverse_lookup - try to find p given f(p) * @fvalue: function value to match, scaled by 1000000 * * Returns closest match for p, also scaled by 1000000 */ u32 tfrc_calc_x_reverse_lookup(u32 fvalue) { int index; if (fvalue == 0) /* f(p) = 0 whenever p = 0 */ return 0; /* Error cases. */ if (fvalue < tfrc_calc_x_lookup[0][1]) { DCCP_WARN("fvalue %u smaller than resolution\n", fvalue); return TFRC_SMALLEST_P; } if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) { DCCP_WARN("fvalue %u exceeds bounds!\n", fvalue); return 1000000; } if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1]) { index = tfrc_binsearch(fvalue, 1); return (index + 1) * TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE; } /* else ... it must be in the coarse-grained column */ index = tfrc_binsearch(fvalue, 0); return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE; } /** * tfrc_invert_loss_event_rate - Compute p so that 10^6 corresponds to 100% * When @loss_event_rate is large, there is a chance that p is truncated to 0. * To avoid re-entering slow-start in that case, we set p = TFRC_SMALLEST_P > 0. */ u32 tfrc_invert_loss_event_rate(u32 loss_event_rate) { if (loss_event_rate == UINT_MAX) /* see RFC 4342, 8.5 */ return 0; if (unlikely(loss_event_rate == 0)) /* map 1/0 into 100% */ return 1000000; return max_t(u32, scaled_div(1, loss_event_rate), TFRC_SMALLEST_P); }