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/*-
* Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
* Copyright (c) 2010 The FreeBSD Foundation
* All rights reserved.
*
* This software was developed by Lawrence Stewart while studying at the Centre
* for Advanced Internet Architectures, Swinburne University of Technology, made
* possible in part by a grant from the Cisco University Research Program Fund
* at Community Foundation Silicon Valley.
*
* Portions of this software were developed at the Centre for Advanced
* Internet Architectures, Swinburne University of Technology, Melbourne,
* Australia by David Hayes under sponsorship from the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD: release/9.1.0/sys/netinet/cc/cc_cubic.h 220560 2011-04-12 08:13:18Z lstewart $
*/
#ifndef _NETINET_CC_CUBIC_H_
#define _NETINET_CC_CUBIC_H_
/* Number of bits of precision for fixed point math calcs. */
#define CUBIC_SHIFT 8
#define CUBIC_SHIFT_4 32
/* 0.5 << CUBIC_SHIFT. */
#define RENO_BETA 128
/* ~0.8 << CUBIC_SHIFT. */
#define CUBIC_BETA 204
/* ~0.2 << CUBIC_SHIFT. */
#define ONE_SUB_CUBIC_BETA 51
/* 3 * ONE_SUB_CUBIC_BETA. */
#define THREE_X_PT2 153
/* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
#define TWO_SUB_PT2 461
/* ~0.4 << CUBIC_SHIFT. */
#define CUBIC_C_FACTOR 102
/* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */
#define CUBIC_FC_FACTOR 230
/* Don't trust s_rtt until this many rtt samples have been taken. */
#define CUBIC_MIN_RTT_SAMPLES 8
/* Userland only bits. */
#ifndef _KERNEL
extern int hz;
/*
* Implementation based on the formulae found in the CUBIC Internet Draft
* "draft-rhee-tcpm-cubic-02".
*
* Note BETA used in cc_cubic is equal to (1-beta) in the I-D
*/
static __inline float
theoretical_cubic_k(double wmax_pkts)
{
double C;
C = 0.4;
return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
}
static __inline unsigned long
theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss)
{
double C, wmax_pkts;
C = 0.4;
wmax_pkts = wmax / (double)smss;
return (smss * (wmax_pkts +
(C * pow(ticks_since_cong / (double)hz -
theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
}
static __inline unsigned long
theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
}
static __inline unsigned long
theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) *
(ticks_since_cong / (float)rtt_ticks) * smss));
}
#endif /* !_KERNEL */
/*
* Compute the CUBIC K value used in the cwnd calculation, using an
* implementation of eqn 2 in the I-D. The method used
* here is adapted from Apple Computer Technical Report #KT-32.
*/
static __inline int64_t
cubic_k(unsigned long wmax_pkts)
{
int64_t s, K;
uint16_t p;
K = s = 0;
p = 0;
/* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
/* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
while (s >= 256) {
s >>= 3;
p++;
}
/*
* Some magic constants taken from the Apple TR with appropriate
* shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
* CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
*/
K = (((s * 275) >> CUBIC_SHIFT) + 98) -
(((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
/* Multiply by 2^p to undo the rebasing of s from above. */
return (K <<= p);
}
/*
* Compute the new cwnd value using an implementation of eqn 1 from the I-D.
* Thanks to Kip Macy for help debugging this function.
*
* XXXLAS: Characterise bounds for overflow.
*/
static __inline unsigned long
cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
{
int64_t cwnd;
/* K is in fixed point form with CUBIC_SHIFT worth of precision. */
/* t - K, with CUBIC_SHIFT worth of precision. */
cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
/* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
cwnd *= (cwnd * cwnd);
/*
* C(t - K)^3 + wmax
* The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
* CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
* and an extra from multiplying through by CUBIC_C_FACTOR.
*/
cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
return ((unsigned long)cwnd);
}
/*
* Compute an approximation of the NewReno cwnd some number of ticks after a
* congestion event. RTT should be the average RTT estimate for the path
* measured over the previous congestion epoch and wmax is the value of cwnd at
* the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
* rather tricky to understand and it turns out this function is not required.
* It is left here for reference.
*/
static __inline unsigned long
reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
/*
* For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT
* W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in
* bytes, we have to multiply by smss.
*/
return (((wmax * RENO_BETA) + (((ticks_since_cong * smss)
<< CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT);
}
/*
* Compute an approximation of the "TCP friendly" cwnd some number of ticks
* after a congestion event that is designed to yield the same average cwnd as
* NewReno while using CUBIC's beta of 0.8. RTT should be the average RTT
* estimate for the path measured over the previous congestion epoch and wmax is
* the value of cwnd at the last congestion event.
*/
static __inline unsigned long
tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
/* Equation 4 of I-D. */
return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong *
smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT);
}
#endif /* _NETINET_CC_CUBIC_H_ */