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diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
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1/*
2 * net/dccp/ccids/lib/tfrc_equation.c
3 *
4 * Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
5 * Copyright (c) 2005 Ian McDonald <iam4@cs.waikato.ac.nz>
6 * Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
7 * Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation; either version 2 of the License, or
12 * (at your option) any later version.
13 */
14
15#include <linux/config.h>
16#include <linux/module.h>
17
18#include <asm/bug.h>
19#include <asm/div64.h>
20
21#include "tfrc.h"
22
23#define TFRC_CALC_X_ARRSIZE 500
24
25#define TFRC_CALC_X_SPLIT 50000
26/* equivalent to 0.05 */
27
28static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = {
29 { 37172, 8172 },
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529};
530
531/* Calculate the send rate as per section 3.1 of RFC3448
532
533Returns send rate in bytes per second
534
535Integer maths and lookups are used as not allowed floating point in kernel
536
537The function for Xcalc as per section 3.1 of RFC3448 is:
538
539X = s
540 -------------------------------------------------------------
541 R*sqrt(2*b*p/3) + (t_RTO * (3*sqrt(3*b*p/8) * p * (1+32*p^2)))
542
543where
544X is the trasmit rate in bytes/second
545s is the packet size in bytes
546R is the round trip time in seconds
547p is the loss event rate, between 0 and 1.0, of the number of loss events
548 as a fraction of the number of packets transmitted
549t_RTO is the TCP retransmission timeout value in seconds
550b is the number of packets acknowledged by a single TCP acknowledgement
551
552we can assume that b = 1 and t_RTO is 4 * R. With this the equation becomes:
553
554X = s
555 -----------------------------------------------------------------------
556 R * sqrt(2 * p / 3) + (12 * R * (sqrt(3 * p / 8) * p * (1 + 32 * p^2)))
557
558
559which we can break down into:
560
561X = s
562 --------
563 R * f(p)
564
565where f(p) = sqrt(2 * p / 3) + (12 * sqrt(3 * p / 8) * p * (1 + 32 * p * p))
566
567Function parameters:
568s - bytes
569R - RTT in usecs
570p - loss rate (decimal fraction multiplied by 1,000,000)
571
572Returns Xcalc in bytes per second
573
574DON'T alter this code unless you run test cases against it as the code
575has been manipulated to stop underflow/overlow.
576
577*/
578u32 tfrc_calc_x(u16 s, u32 R, u32 p)
579{
580 int index;
581 u32 f;
582 u64 tmp1, tmp2;
583
584 if (p < TFRC_CALC_X_SPLIT)
585 index = (p / (TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE)) - 1;
586 else
587 index = (p / (1000000 / TFRC_CALC_X_ARRSIZE)) - 1;
588
589 if (index < 0)
590 /* p should be 0 unless there is a bug in my code */
591 index = 0;
592
593 if (R == 0)
594 R = 1; /* RTT can't be zero or else divide by zero */
595
596 BUG_ON(index >= TFRC_CALC_X_ARRSIZE);
597
598 if (p >= TFRC_CALC_X_SPLIT)
599 f = tfrc_calc_x_lookup[index][0];
600 else
601 f = tfrc_calc_x_lookup[index][1];
602
603 tmp1 = ((u64)s * 100000000);
604 tmp2 = ((u64)R * (u64)f);
605 do_div(tmp2, 10000);
606 do_div(tmp1, tmp2);
607 /* Don't alter above math unless you test due to overflow on 32 bit */
608
609 return (u32)tmp1;
610}
611
612EXPORT_SYMBOL_GPL(tfrc_calc_x);
613
614/*
615 * args: fvalue - function value to match
616 * returns: p closest to that value
617 *
618 * both fvalue and p are multiplied by 1,000,000 to use ints
619 */
620u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
621{
622 int ctr = 0;
623 int small;
624
625 if (fvalue < tfrc_calc_x_lookup[0][1])
626 return 0;
627
628 if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1])
629 small = 1;
630 else if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0])
631 return 1000000;
632 else
633 small = 0;
634
635 while (fvalue > tfrc_calc_x_lookup[ctr][small])
636 ctr++;
637
638 if (small)
639 return TFRC_CALC_X_SPLIT * ctr / TFRC_CALC_X_ARRSIZE;
640 else
641 return 1000000 * ctr / TFRC_CALC_X_ARRSIZE;
642}
643
644EXPORT_SYMBOL_GPL(tfrc_calc_x_reverse_lookup);
generated by cgit v1.2.2 (git 2.25.0) at 2024-12-25 01:31:32 -0500