706 lines
19 KiB
C
706 lines
19 KiB
C
/*
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* Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
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* Copyright (c) 2005 Ian McDonald <ian.mcdonald@jandi.co.nz>
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* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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* Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*/
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#include <linux/module.h>
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#include "../../dccp.h"
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#include "tfrc.h"
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#define TFRC_CALC_X_ARRSIZE 500
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#define TFRC_CALC_X_SPLIT 50000 /* 0.05 * 1000000, details below */
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#define TFRC_SMALLEST_P (TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE)
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/*
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TFRC TCP Reno Throughput Equation Lookup Table for f(p)
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The following two-column lookup table implements a part of the TCP throughput
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equation from [RFC 3448, sec. 3.1]:
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s
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X_calc = --------------------------------------------------------------
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R * sqrt(2*b*p/3) + (3 * t_RTO * sqrt(3*b*p/8) * (p + 32*p^3))
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Where:
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X is the transmit rate in bytes/second
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s is the packet size in bytes
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R is the round trip time in seconds
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p is the loss event rate, between 0 and 1.0, of the number of loss
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events as a fraction of the number of packets transmitted
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t_RTO is the TCP retransmission timeout value in seconds
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b is the number of packets acknowledged by a single TCP ACK
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We can assume that b = 1 and t_RTO is 4 * R. The equation now becomes:
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s
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X_calc = -------------------------------------------------------
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R * sqrt(p*2/3) + (12 * R * sqrt(p*3/8) * (p + 32*p^3))
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which we can break down into:
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s
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X_calc = ---------
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R * f(p)
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where f(p) is given for 0 < p <= 1 by:
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f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (p + 32*p^3)
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Since this is kernel code, floating-point arithmetic is avoided in favour of
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integer arithmetic. This means that nearly all fractional parameters are
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scaled by 1000000:
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* the parameters p and R
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* the return result f(p)
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The lookup table therefore actually tabulates the following function g(q):
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g(q) = 1000000 * f(q/1000000)
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Hence, when p <= 1, q must be less than or equal to 1000000. To achieve finer
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granularity for the practically more relevant case of small values of p (up to
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5%), the second column is used; the first one ranges up to 100%. This split
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corresponds to the value of q = TFRC_CALC_X_SPLIT. At the same time this also
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determines the smallest resolution possible with this lookup table:
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TFRC_SMALLEST_P = TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE
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The entire table is generated by:
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for(i=0; i < TFRC_CALC_X_ARRSIZE; i++) {
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lookup[i][0] = g((i+1) * 1000000/TFRC_CALC_X_ARRSIZE);
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lookup[i][1] = g((i+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE);
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}
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With the given configuration, we have, with M = TFRC_CALC_X_ARRSIZE-1,
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lookup[0][0] = g(1000000/(M+1)) = 1000000 * f(0.2%)
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lookup[M][0] = g(1000000) = 1000000 * f(100%)
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lookup[0][1] = g(TFRC_SMALLEST_P) = 1000000 * f(0.01%)
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lookup[M][1] = g(TFRC_CALC_X_SPLIT) = 1000000 * f(5%)
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In summary, the two columns represent f(p) for the following ranges:
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* The first column is for 0.002 <= p <= 1.0
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* The second column is for 0.0001 <= p <= 0.05
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Where the columns overlap, the second (finer-grained) is given preference,
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i.e. the first column is used only for p >= 0.05.
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*/
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static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = {
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{ 37172, 8172 },
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{ 53499, 11567 },
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{ 66664, 14180 },
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{ 78298, 16388 },
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{ 89021, 18339 },
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{ 99147, 20108 },
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{ 108858, 21738 },
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{ 118273, 23260 },
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{ 127474, 24693 },
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{ 136520, 26052 },
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{ 145456, 27348 },
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{ 154316, 28589 },
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{ 163130, 29783 },
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{ 171919, 30935 },
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{ 180704, 32049 },
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{ 189502, 33130 },
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{ 198328, 34180 },
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{ 207194, 35202 },
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{ 216114, 36198 },
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{ 225097, 37172 },
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{ 234153, 38123 },
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{ 243294, 39055 },
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{ 252527, 39968 },
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{ 261861, 40864 },
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{ 271305, 41743 },
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{ 280866, 42607 },
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{ 290553, 43457 },
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{ 300372, 44293 },
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{ 310333, 45117 },
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{ 320441, 45929 },
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{ 330705, 46729 },
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{ 341131, 47518 },
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{ 351728, 48297 },
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{ 362501, 49066 },
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{ 373460, 49826 },
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{ 384609, 50577 },
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{ 395958, 51320 },
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{ 407513, 52054 },
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{ 419281, 52780 },
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{ 431270, 53499 },
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{ 443487, 54211 },
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{ 455940, 54916 },
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{ 468635, 55614 },
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{ 481581, 56306 },
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{ 494785, 56991 },
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{ 508254, 57671 },
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{ 521996, 58345 },
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{ 536019, 59014 },
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{ 550331, 59677 },
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{ 564939, 60335 },
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{ 579851, 60988 },
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{ 595075, 61636 },
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{ 610619, 62279 },
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{ 626491, 62918 },
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{ 642700, 63553 },
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{ 659253, 64183 },
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{ 676158, 64809 },
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{ 693424, 65431 },
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{ 711060, 66050 },
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{ 729073, 66664 },
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{ 747472, 67275 },
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{ 766266, 67882 },
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{ 785464, 68486 },
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{ 805073, 69087 },
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{ 825103, 69684 },
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{ 845562, 70278 },
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{ 866460, 70868 },
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{ 887805, 71456 },
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{ 909606, 72041 },
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{ 931873, 72623 },
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{ 954614, 73202 },
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{ 977839, 73778 },
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{ 1001557, 74352 },
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{ 1025777, 74923 },
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{ 1050508, 75492 },
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{ 1075761, 76058 },
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{ 1101544, 76621 },
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{ 1127867, 77183 },
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{ 1154739, 77741 },
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{ 1182172, 78298 },
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{ 1210173, 78852 },
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{ 1238753, 79405 },
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{ 1267922, 79955 },
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{ 1297689, 80503 },
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{ 1328066, 81049 },
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{ 1359060, 81593 },
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{ 1390684, 82135 },
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{ 1422947, 82675 },
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{ 1455859, 83213 },
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{ 1489430, 83750 },
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{ 1523671, 84284 },
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{ 1558593, 84817 },
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{ 1594205, 85348 },
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{ 1630518, 85878 },
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{ 1667543, 86406 },
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{ 1705290, 86932 },
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{ 1743770, 87457 },
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{ 1782994, 87980 },
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{ 1822973, 88501 },
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{ 1863717, 89021 },
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{ 1905237, 89540 },
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{ 1947545, 90057 },
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{ 1990650, 90573 },
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{ 2034566, 91087 },
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{ 2079301, 91600 },
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{ 2124869, 92111 },
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{ 2171279, 92622 },
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{ 2218543, 93131 },
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{ 2266673, 93639 },
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{ 2315680, 94145 },
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{ 2365575, 94650 },
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{ 2416371, 95154 },
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{ 2468077, 95657 },
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{ 2520707, 96159 },
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{ 2574271, 96660 },
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{ 2628782, 97159 },
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{ 2684250, 97658 },
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{ 2740689, 98155 },
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{ 2798110, 98651 },
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{ 2856524, 99147 },
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{ 2915944, 99641 },
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{ 2976382, 100134 },
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{ 3037850, 100626 },
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{ 3100360, 101117 },
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{ 3163924, 101608 },
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{ 3228554, 102097 },
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{ 3294263, 102586 },
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{ 3361063, 103073 },
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{ 3428966, 103560 },
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{ 3497984, 104045 },
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{ 3568131, 104530 },
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{ 3639419, 105014 },
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{ 3711860, 105498 },
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{ 3785467, 105980 },
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{ 3860253, 106462 },
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{ 3936229, 106942 },
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{ 4013410, 107422 },
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{ 4091808, 107902 },
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{ 4252306, 108858 },
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{ 5132223, 113597 },
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{ 5522299, 115474 },
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{ 5623389, 115942 },
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{ 5725934, 116409 },
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{ 5829948, 116876 },
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{ 5935446, 117342 },
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{ 6042439, 117808 },
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{ 6150943, 118273 },
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{ 6260972, 118738 },
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{ 6372538, 119202 },
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{ 6485657, 119665 },
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{ 6600342, 120128 },
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{ 6716607, 120591 },
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{ 6834467, 121053 },
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{ 6953935, 121514 },
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{ 7075025, 121976 },
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{ 7197752, 122436 },
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{ 7322131, 122896 },
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{ 7448175, 123356 },
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{ 7575898, 123815 },
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{ 7705316, 124274 },
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{ 7836442, 124733 },
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{ 7969291, 125191 },
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{ 8103877, 125648 },
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{ 8240216, 126105 },
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{ 8378321, 126562 },
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{ 8518208, 127018 },
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{ 8659890, 127474 },
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{ 8803384, 127930 },
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{ 8948702, 128385 },
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{ 9095861, 128840 },
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{ 9244875, 129294 },
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{ 9395760, 129748 },
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{ 9548529, 130202 },
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{ 9703198, 130655 },
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{ 10018296, 131561 },
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{ 11712924, 136071 },
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{ 12076536, 136969 },
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{ 17870643, 149007 },
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{ 98142366, 217457 },
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{ 99010679, 217905 },
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{ 99884556, 218353 },
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{ 100764018, 218801 },
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{ 101649086, 219250 },
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{ 102539782, 219698 },
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{ 103436128, 220147 },
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{ 104338146, 220596 },
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{ 105245857, 221046 },
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{ 106159284, 221495 },
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{ 107078448, 221945 },
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{ 108003370, 222394 },
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{ 108934074, 222844 },
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{ 109870580, 223294 },
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{ 110812910, 223745 },
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{ 111761087, 224195 },
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{ 112715133, 224646 },
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{ 113675069, 225097 },
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{ 114640918, 225548 },
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{ 115612702, 225999 },
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{ 116590442, 226450 },
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{ 117574162, 226902 },
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{ 118563882, 227353 },
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{ 119559626, 227805 },
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{ 120561415, 228258 },
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{ 121569272, 228710 },
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{ 122583219, 229162 },
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{ 123603278, 229615 },
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{ 124629471, 230068 },
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{ 125661822, 230521 },
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{ 126700352, 230974 },
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{ 127745083, 231428 },
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{ 128796039, 231882 },
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{ 129853241, 232336 },
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{ 130916713, 232790 },
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{ 131986475, 233244 },
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{ 133062553, 233699 },
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{ 134144966, 234153 },
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{ 135233739, 234608 },
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{ 136328894, 235064 },
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{ 137430453, 235519 },
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{ 138538440, 235975 },
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{ 139652876, 236430 },
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{ 140773786, 236886 },
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{ 141901190, 237343 },
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{ 143035113, 237799 },
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{ 144175576, 238256 },
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{ 145322604, 238713 },
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{ 146476218, 239170 },
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{ 147636442, 239627 },
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{ 148803298, 240085 },
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{ 149976809, 240542 },
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{ 151156999, 241000 },
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{ 152343890, 241459 },
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{ 153537506, 241917 },
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{ 154737869, 242376 },
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{ 155945002, 242835 },
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{ 157158929, 243294 },
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{ 158379673, 243753 },
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{ 159607257, 244213 },
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{ 160841704, 244673 },
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{ 162083037, 245133 },
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{ 163331279, 245593 },
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{ 164586455, 246054 },
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{ 165848586, 246514 },
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{ 167117696, 246975 },
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{ 168393810, 247437 },
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{ 169676949, 247898 },
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{ 170967138, 248360 },
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{ 172264399, 248822 },
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{ 173568757, 249284 },
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{ 174880235, 249747 },
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{ 176198856, 250209 },
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{ 177524643, 250672 },
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{ 178857621, 251136 },
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{ 180197813, 251599 },
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{ 181545242, 252063 },
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{ 182899933, 252527 },
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{ 184261908, 252991 },
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{ 185631191, 253456 },
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{ 187007807, 253920 },
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{ 188391778, 254385 },
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{ 189783129, 254851 },
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{ 191181884, 255316 },
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{ 192588065, 255782 },
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{ 194001698, 256248 },
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{ 195422805, 256714 },
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{ 196851411, 257181 },
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{ 198287540, 257648 },
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{ 199731215, 258115 },
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{ 201182461, 258582 },
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{ 202641302, 259050 },
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{ 204107760, 259518 },
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{ 205581862, 259986 },
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{ 207063630, 260454 },
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{ 208553088, 260923 },
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{ 210050262, 261392 },
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{ 211555174, 261861 },
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{ 213067849, 262331 },
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{ 214588312, 262800 },
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{ 216116586, 263270 },
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{ 217652696, 263741 },
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{ 219196666, 264211 },
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{ 220748520, 264682 },
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{ 222308282, 265153 },
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{ 223875978, 265625 },
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{ 225451630, 266097 },
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{ 227035265, 266569 },
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{ 228626905, 267041 },
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{ 230226576, 267514 },
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{ 231834302, 267986 },
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|
{ 233450107, 268460 },
|
|
{ 235074016, 268933 },
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|
{ 236706054, 269407 },
|
|
{ 238346244, 269881 },
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|
{ 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);
|
|
}
|