2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
5 * Copyright (c) 2010 The FreeBSD Foundation
8 * This software was developed by Lawrence Stewart while studying at the Centre
9 * for Advanced Internet Architectures, Swinburne University of Technology, made
10 * possible in part by a grant from the Cisco University Research Program Fund
11 * at Community Foundation Silicon Valley.
13 * Portions of this software were developed at the Centre for Advanced
14 * Internet Architectures, Swinburne University of Technology, Melbourne,
15 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
41 #ifndef _NETINET_CC_CUBIC_H_
42 #define _NETINET_CC_CUBIC_H_
44 #include <sys/limits.h>
46 /* Number of bits of precision for fixed point math calcs. */
49 #define CUBIC_SHIFT_4 32
51 /* 0.5 << CUBIC_SHIFT. */
54 /* ~0.7 << CUBIC_SHIFT. */
55 #define CUBIC_BETA 179
57 /* ~0.3 << CUBIC_SHIFT. */
58 #define ONE_SUB_CUBIC_BETA 77
60 /* 3 * ONE_SUB_CUBIC_BETA. */
61 #define THREE_X_PT3 231
63 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
64 #define TWO_SUB_PT3 435
66 /* ~0.4 << CUBIC_SHIFT. */
67 #define CUBIC_C_FACTOR 102
69 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */
70 #define CUBIC_FC_FACTOR 217
72 /* Don't trust s_rtt until this many rtt samples have been taken. */
73 #define CUBIC_MIN_RTT_SAMPLES 8
75 /* Userland only bits. */
81 * Implementation based on the formulae found in the CUBIC Internet Draft
82 * "draft-ietf-tcpm-cubic-04".
87 theoretical_cubic_k(double wmax_pkts)
93 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
96 static __inline unsigned long
97 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss)
102 wmax_pkts = wmax / (double)smss;
104 return (smss * (wmax_pkts +
105 (C * pow(ticks_since_cong / (double)hz -
106 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
109 static __inline unsigned long
110 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
114 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
117 static __inline unsigned long
118 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
122 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) *
123 (ticks_since_cong / (float)rtt_ticks) * smss));
126 #endif /* !_KERNEL */
129 * Compute the CUBIC K value used in the cwnd calculation, using an
130 * implementation of eqn 2 in the I-D. The method used
131 * here is adapted from Apple Computer Technical Report #KT-32.
133 static __inline int64_t
134 cubic_k(unsigned long wmax_pkts)
142 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
143 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
145 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
152 * Some magic constants taken from the Apple TR with appropriate
153 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
154 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
156 K = (((s * 275) >> CUBIC_SHIFT) + 98) -
157 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
159 /* Multiply by 2^p to undo the rebasing of s from above. */
164 * Compute the new cwnd value using an implementation of eqn 1 from the I-D.
165 * Thanks to Kip Macy for help debugging this function.
167 static __inline unsigned long
168 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
172 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */
174 /* t - K, with CUBIC_SHIFT worth of precision. */
175 cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
177 /* moved this calculation up because it cannot overflow or underflow */
178 cwnd *= CUBIC_C_FACTOR * smss;
180 if (cwnd > 2097151) /* 2^21 cubed is long max */
183 if (cwnd < -2097152) /* -2^21 cubed is long min */
186 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
187 cwnd *= (cwnd * cwnd);
191 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
192 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
193 * and an extra from multiplying through by CUBIC_C_FACTOR.
195 * The original formula was this:
196 * cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
198 * CUBIC_C_FACTOR and smss factors were moved up to an earlier
199 * calculation to simplify overflow and underflow detection.
201 cwnd = (cwnd >> CUBIC_SHIFT_4) + wmax;
206 return ((unsigned long)cwnd);
210 * Compute an approximation of the NewReno cwnd some number of ticks after a
211 * congestion event. RTT should be the average RTT estimate for the path
212 * measured over the previous congestion epoch and wmax is the value of cwnd at
213 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
214 * rather tricky to understand and it turns out this function is not required.
215 * It is left here for reference.
217 static __inline unsigned long
218 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
223 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT
224 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in
225 * bytes, we have to multiply by smss.
227 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss)
228 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT);
232 * Compute an approximation of the "TCP friendly" cwnd some number of ticks
233 * after a congestion event that is designed to yield the same average cwnd as
234 * NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT
235 * estimate for the path measured over the previous congestion epoch and wmax is
236 * the value of cwnd at the last congestion event.
238 static __inline unsigned long
239 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
243 /* Equation 4 of I-D. */
244 return (((wmax * CUBIC_BETA) + (((THREE_X_PT3 * ticks_since_cong *
245 smss) << CUBIC_SHIFT) / TWO_SUB_PT3 / rtt_ticks)) >> CUBIC_SHIFT);
248 #endif /* _NETINET_CC_CUBIC_H_ */