Current File : //backups/router/usr/include/netinet/cc/cc_cubic.h
/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* 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.
*/
#ifndef _NETINET_CC_CUBIC_H_
#define _NETINET_CC_CUBIC_H_
#include <sys/limits.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
/* ~0.7 << CUBIC_SHIFT. */
#define CUBIC_BETA 179
/* ~0.3 << CUBIC_SHIFT. */
#define ONE_SUB_CUBIC_BETA 77
/* 3 * ONE_SUB_CUBIC_BETA. */
#define THREE_X_PT3 231
/* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
#define TWO_SUB_PT3 435
/* ~0.4 << CUBIC_SHIFT. */
#define CUBIC_C_FACTOR 102
/* CUBIC fast convergence factor: (1+beta_cubic)/2. */
#define CUBIC_FC_FACTOR 217
/* Don't trust s_rtt until this many rtt samples have been taken. */
#define CUBIC_MIN_RTT_SAMPLES 8
/*
* (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor
* and taking cube-root yields 448845 as the effective useful limit
*/
#define CUBED_ROOT_MAX_ULONG 448845
/* Flags used in the cubic structure */
#define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */
#define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */
#define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */
#define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */
#define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */
#define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */
/* Kernel only bits */
#ifdef _KERNEL
struct cubic {
/* CUBIC K in fixed point form with CUBIC_SHIFT worth of precision. */
int64_t K;
/* Sum of RTT samples across an epoch in usecs. */
int64_t sum_rtt_usecs;
/* Size of cwnd just before cwnd was reduced in the last congestion event */
uint64_t W_max;
/* An estimate for the congestion window in the Reno-friendly region */
uint64_t W_est;
/* The cwnd at the beginning of the current congestion avoidance stage */
uint64_t cwnd_epoch;
/*
* Size of cwnd at the time of setting ssthresh most recently,
* either upon exiting the first slow start, or just before cwnd
* was reduced in the last congestion event
*/
uint64_t cwnd_prior;
/* various flags */
uint32_t flags;
/* Minimum observed rtt in usecs. */
int min_rtt_usecs;
/* Mean observed rtt between congestion epochs. */
int mean_rtt_usecs;
/* ACKs since last congestion event. */
int epoch_ack_count;
/* Timestamp (in ticks) at which the current CA epoch started. */
int t_epoch;
/* Timestamp (in ticks) at which the previous CA epoch started. */
int undo_t_epoch;
/* Few variables to restore the state after RTO_ERR */
int64_t undo_K;
uint64_t undo_cwnd_prior;
uint64_t undo_W_max;
uint64_t undo_W_est;
uint64_t undo_cwnd_epoch;
/* Number of congestion events experienced */
uint64_t num_cong_events;
uint32_t css_baseline_minrtt;
uint32_t css_current_round_minrtt;
uint32_t css_lastround_minrtt;
uint32_t css_rttsample_count;
uint32_t css_entered_at_round;
uint32_t css_current_round;
uint32_t css_fas_at_css_entry;
uint32_t css_lowrtt_fas;
uint32_t css_last_fas;
};
#endif
/* Userland only bits. */
#ifndef _KERNEL
extern int hz;
/*
* Implementation based on the formulae found in the CUBIC Internet Draft
* "draft-ietf-tcpm-cubic-04".
*
*/
static __inline float
theoretical_cubic_k(double wmax_pkts)
{
double C;
C = 0.4;
return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
}
static __inline unsigned long
theoretical_cubic_cwnd(int ticks_since_epoch, 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_epoch / (double)hz -
theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
}
static __inline unsigned long
theoretical_reno_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
return ((wmax * 0.5) + ((ticks_since_epoch / (float)rtt_ticks) * smss));
}
static __inline unsigned long
theoretical_tf_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax,
uint32_t smss)
{
return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) *
(ticks_since_epoch / (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 usecs_since_epoch, 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)usecs_since_epoch << CUBIC_SHIFT) - (K * hz * tick)) /
(hz * tick);
if (cwnd > CUBED_ROOT_MAX_ULONG)
return INT_MAX;
if (cwnd < -CUBED_ROOT_MAX_ULONG)
return 0;
/* (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) >> CUBIC_SHIFT_4) * smss + wmax;
/*
* for negative cwnd, limiting to zero as lower bound
*/
return (lmax(0,cwnd));
}
/*
* Compute an approximation of the NewReno cwnd some number of usecs 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.
*
* XXX: Not used
*/
static __inline unsigned long
reno_cwnd(int usecs_since_epoch, int rtt_usecs, 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) + (((usecs_since_epoch * smss)
<< CUBIC_SHIFT) / rtt_usecs)) >> CUBIC_SHIFT);
}
/*
* Compute an approximation of the "TCP friendly" cwnd some number of usecs
* after a congestion event that is designed to yield the same average cwnd as
* NewReno while using CUBIC's beta of 0.7. 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 usecs_since_epoch, int rtt_usecs, unsigned long wmax,
uint32_t smss)
{
/* Equation 4 of I-D. */
return (((wmax * CUBIC_BETA) +
(((THREE_X_PT3 * (unsigned long)usecs_since_epoch *
(unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_usecs)))
>> CUBIC_SHIFT);
}
#endif /* _NETINET_CC_CUBIC_H_ */
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