a3cbdde8e9
This implements [RFC 3448, 4.5], which performs congestion avoidance behaviour by reducing the transmit rate as the queueing delay (measured in terms of long-term RTT) increases. Oscillation can be turned on/off via a module option (do_osc_prev) and via sysfs (using mode 0644), the default is off. Overflow analysis: ------------------ * oscillation prevention is done after update_x(), so that t_ipi <= 64000; * hence the multiplication "t_ipi * sqrt(R_sample)" needs 64 bits; * done using u64 for sqrt_sample and explicit typecast of t_ipi; * the divisor, R_sqmean, is non-zero because oscillation prevention is first called when receiving the second feedback packet, and tfrc_scaled_rtt() > 0. A detailed discussion of the algorithm (with plots) is on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ccid3/sender_notes/oscillation_prevention/ The algorithm has negative side effects: * when allowing to decrease t_ipi (leads to a large RTT) and * when using it during slow-start; both uses are therefore disabled. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
85 lines
2.7 KiB
C
85 lines
2.7 KiB
C
#ifndef _TFRC_H_
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#define _TFRC_H_
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/*
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* net/dccp/ccids/lib/tfrc.h
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*
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* Copyright (c) 2007 The University of Aberdeen, Scotland, UK
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* Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
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* Copyright (c) 2005-6 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/types.h>
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#include <linux/math64.h>
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#include "../../dccp.h"
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/* internal includes that this module exports: */
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#include "loss_interval.h"
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#include "packet_history.h"
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#ifdef CONFIG_IP_DCCP_TFRC_DEBUG
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extern int tfrc_debug;
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#define tfrc_pr_debug(format, a...) DCCP_PR_DEBUG(tfrc_debug, format, ##a)
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#else
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#define tfrc_pr_debug(format, a...)
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#endif
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/* integer-arithmetic divisions of type (a * 1000000)/b */
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static inline u64 scaled_div(u64 a, u64 b)
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{
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BUG_ON(b==0);
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return div64_u64(a * 1000000, b);
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}
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static inline u32 scaled_div32(u64 a, u64 b)
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{
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u64 result = scaled_div(a, b);
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if (result > UINT_MAX) {
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DCCP_CRIT("Overflow: %llu/%llu > UINT_MAX",
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(unsigned long long)a, (unsigned long long)b);
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return UINT_MAX;
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}
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return result;
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}
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/**
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* tfrc_scaled_sqrt - Compute scaled integer sqrt(x) for 0 < x < 2^22-1
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* Uses scaling to improve accuracy of the integer approximation of sqrt(). The
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* scaling factor of 2^10 limits the maximum @sample to 4e6; this is okay for
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* clamped RTT samples (dccp_sample_rtt).
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* Should best be used for expressions of type sqrt(x)/sqrt(y), since then the
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* scaling factor is neutralised. For this purpose, it avoids returning zero.
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*/
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static inline u16 tfrc_scaled_sqrt(const u32 sample)
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{
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const unsigned long non_zero_sample = sample ? : 1;
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return int_sqrt(non_zero_sample << 10);
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}
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/**
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* tfrc_ewma - Exponentially weighted moving average
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* @weight: Weight to be used as damping factor, in units of 1/10
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*/
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static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight)
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{
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return avg ? (weight * avg + (10 - weight) * newval) / 10 : newval;
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}
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extern u32 tfrc_calc_x(u16 s, u32 R, u32 p);
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extern u32 tfrc_calc_x_reverse_lookup(u32 fvalue);
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extern u32 tfrc_invert_loss_event_rate(u32 loss_event_rate);
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extern int tfrc_tx_packet_history_init(void);
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extern void tfrc_tx_packet_history_exit(void);
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extern int tfrc_rx_packet_history_init(void);
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extern void tfrc_rx_packet_history_exit(void);
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extern int tfrc_li_init(void);
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extern void tfrc_li_exit(void);
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#endif /* _TFRC_H_ */
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