c9eaf17341
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org> Signed-off-by: David S. Miller <davem@davemloft.net>
697 lines
18 KiB
C
697 lines
18 KiB
C
/*
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* net/dccp/ccids/lib/tfrc_equation.c
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*
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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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{ 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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{ 171919, 30935 },
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{ 207194, 35202 },
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{ 95570590, 216114 },
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{ 96422343, 216561 },
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{ 97279594, 217009 },
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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 },
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{ 235074016, 268933 },
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|
{ 236706054, 269407 },
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|
{ 238346244, 269881 },
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{ 239994613, 270355 },
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|
{ 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);
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(tfrc_calc_x);
|
|
|
|
/*
|
|
* 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 %d smaller than resolution\n", fvalue);
|
|
return tfrc_calc_x_lookup[0][1];
|
|
}
|
|
if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {
|
|
DCCP_WARN("fvalue %d 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;
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(tfrc_calc_x_reverse_lookup);
|