1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org> 5 * Copyright (c) 2010 The FreeBSD Foundation 6 * All rights reserved. 7 * 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. 12 * 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. 16 * 17 * Redistribution and use in source and binary forms, with or without 18 * modification, are permitted provided that the following conditions 19 * are met: 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. 25 * 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 36 * SUCH DAMAGE. 37 * 38 * $FreeBSD$ 39 */ 40 41 #ifndef _NETINET_CC_CUBIC_H_ 42 #define _NETINET_CC_CUBIC_H_ 43 44 /* Number of bits of precision for fixed point math calcs. */ 45 #define CUBIC_SHIFT 8 46 47 #define CUBIC_SHIFT_4 32 48 49 /* 0.5 << CUBIC_SHIFT. */ 50 #define RENO_BETA 128 51 52 /* ~0.7 << CUBIC_SHIFT. */ 53 #define CUBIC_BETA 179 54 55 /* ~0.3 << CUBIC_SHIFT. */ 56 #define ONE_SUB_CUBIC_BETA 77 57 58 /* 3 * ONE_SUB_CUBIC_BETA. */ 59 #define THREE_X_PT3 231 60 61 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ 62 #define TWO_SUB_PT3 435 63 64 /* ~0.4 << CUBIC_SHIFT. */ 65 #define CUBIC_C_FACTOR 102 66 67 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */ 68 #define CUBIC_FC_FACTOR 217 69 70 /* Don't trust s_rtt until this many rtt samples have been taken. */ 71 #define CUBIC_MIN_RTT_SAMPLES 8 72 73 /* Userland only bits. */ 74 #ifndef _KERNEL 75 76 extern int hz; 77 78 /* 79 * Implementation based on the formulae found in the CUBIC Internet Draft 80 * "draft-ietf-tcpm-cubic-04". 81 * 82 */ 83 84 static __inline float 85 theoretical_cubic_k(double wmax_pkts) 86 { 87 double C; 88 89 C = 0.4; 90 91 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 92 } 93 94 static __inline unsigned long 95 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) 96 { 97 double C, wmax_pkts; 98 99 C = 0.4; 100 wmax_pkts = wmax / (double)smss; 101 102 return (smss * (wmax_pkts + 103 (C * pow(ticks_since_cong / (double)hz - 104 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 105 } 106 107 static __inline unsigned long 108 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 109 uint32_t smss) 110 { 111 112 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 113 } 114 115 static __inline unsigned long 116 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 117 uint32_t smss) 118 { 119 120 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) * 121 (ticks_since_cong / (float)rtt_ticks) * smss)); 122 } 123 124 #endif /* !_KERNEL */ 125 126 /* 127 * Compute the CUBIC K value used in the cwnd calculation, using an 128 * implementation of eqn 2 in the I-D. The method used 129 * here is adapted from Apple Computer Technical Report #KT-32. 130 */ 131 static __inline int64_t 132 cubic_k(unsigned long wmax_pkts) 133 { 134 int64_t s, K; 135 uint16_t p; 136 137 K = s = 0; 138 p = 0; 139 140 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 141 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 142 143 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 144 while (s >= 256) { 145 s >>= 3; 146 p++; 147 } 148 149 /* 150 * Some magic constants taken from the Apple TR with appropriate 151 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 152 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 153 */ 154 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 155 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 156 157 /* Multiply by 2^p to undo the rebasing of s from above. */ 158 return (K <<= p); 159 } 160 161 /* 162 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 163 * Thanks to Kip Macy for help debugging this function. 164 * 165 * XXXLAS: Characterise bounds for overflow. 166 */ 167 static __inline unsigned long 168 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) 169 { 170 int64_t cwnd; 171 172 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ 173 174 /* t - K, with CUBIC_SHIFT worth of precision. */ 175 cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; 176 177 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 178 cwnd *= (cwnd * cwnd); 179 180 /* 181 * C(t - K)^3 + wmax 182 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 183 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 184 * and an extra from multiplying through by CUBIC_C_FACTOR. 185 */ 186 cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax; 187 188 return ((unsigned long)cwnd); 189 } 190 191 /* 192 * Compute an approximation of the NewReno cwnd some number of ticks after a 193 * congestion event. RTT should be the average RTT estimate for the path 194 * measured over the previous congestion epoch and wmax is the value of cwnd at 195 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is 196 * rather tricky to understand and it turns out this function is not required. 197 * It is left here for reference. 198 */ 199 static __inline unsigned long 200 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 201 uint32_t smss) 202 { 203 204 /* 205 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT 206 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in 207 * bytes, we have to multiply by smss. 208 */ 209 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) 210 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); 211 } 212 213 /* 214 * Compute an approximation of the "TCP friendly" cwnd some number of ticks 215 * after a congestion event that is designed to yield the same average cwnd as 216 * NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT 217 * estimate for the path measured over the previous congestion epoch and wmax is 218 * the value of cwnd at the last congestion event. 219 */ 220 static __inline unsigned long 221 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 222 uint32_t smss) 223 { 224 225 /* Equation 4 of I-D. */ 226 return (((wmax * CUBIC_BETA) + (((THREE_X_PT3 * ticks_since_cong * 227 smss) << CUBIC_SHIFT) / TWO_SUB_PT3 / rtt_ticks)) >> CUBIC_SHIFT); 228 } 229 230 #endif /* _NETINET_CC_CUBIC_H_ */ 231