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 #include <sys/limits.h> 45 46 /* Number of bits of precision for fixed point math calcs. */ 47 #define CUBIC_SHIFT 8 48 49 #define CUBIC_SHIFT_4 32 50 51 /* 0.5 << CUBIC_SHIFT. */ 52 #define RENO_BETA 128 53 54 /* ~0.8 << CUBIC_SHIFT. */ 55 #define CUBIC_BETA 204 56 57 /* ~0.2 << CUBIC_SHIFT. */ 58 #define ONE_SUB_CUBIC_BETA 51 59 60 /* 3 * ONE_SUB_CUBIC_BETA. */ 61 #define THREE_X_PT2 153 62 63 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ 64 #define TWO_SUB_PT2 461 65 66 /* ~0.4 << CUBIC_SHIFT. */ 67 #define CUBIC_C_FACTOR 102 68 69 /* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */ 70 #define CUBIC_FC_FACTOR 230 71 72 /* Don't trust s_rtt until this many rtt samples have been taken. */ 73 #define CUBIC_MIN_RTT_SAMPLES 8 74 75 /* Userland only bits. */ 76 #ifndef _KERNEL 77 78 extern int hz; 79 80 /* 81 * Implementation based on the formulae found in the CUBIC Internet Draft 82 * "draft-rhee-tcpm-cubic-02". 83 * 84 * Note BETA used in cc_cubic is equal to (1-beta) in the I-D 85 */ 86 87 static __inline float 88 theoretical_cubic_k(double wmax_pkts) 89 { 90 double C; 91 92 C = 0.4; 93 94 return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 95 } 96 97 static __inline unsigned long 98 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) 99 { 100 double C, wmax_pkts; 101 102 C = 0.4; 103 wmax_pkts = wmax / (double)smss; 104 105 return (smss * (wmax_pkts + 106 (C * pow(ticks_since_cong / (double)hz - 107 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 108 } 109 110 static __inline unsigned long 111 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 112 uint32_t smss) 113 { 114 115 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 116 } 117 118 static __inline unsigned long 119 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 120 uint32_t smss) 121 { 122 123 return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) * 124 (ticks_since_cong / (float)rtt_ticks) * smss)); 125 } 126 127 #endif /* !_KERNEL */ 128 129 /* 130 * Compute the CUBIC K value used in the cwnd calculation, using an 131 * implementation of eqn 2 in the I-D. The method used 132 * here is adapted from Apple Computer Technical Report #KT-32. 133 */ 134 static __inline int64_t 135 cubic_k(unsigned long wmax_pkts) 136 { 137 int64_t s, K; 138 uint16_t p; 139 140 K = s = 0; 141 p = 0; 142 143 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 144 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 145 146 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 147 while (s >= 256) { 148 s >>= 3; 149 p++; 150 } 151 152 /* 153 * Some magic constants taken from the Apple TR with appropriate 154 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 155 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 156 */ 157 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 158 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 159 160 /* Multiply by 2^p to undo the rebasing of s from above. */ 161 return (K <<= p); 162 } 163 164 /* 165 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 166 * Thanks to Kip Macy for help debugging this function. 167 */ 168 static __inline unsigned long 169 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) 170 { 171 int64_t cwnd; 172 173 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ 174 175 /* t - K, with CUBIC_SHIFT worth of precision. */ 176 cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; 177 178 /* moved this calculation up because it cannot overflow or underflow */ 179 cwnd *= CUBIC_C_FACTOR * smss; 180 181 if (cwnd > 2097151) /* 2^21 cubed is long max */ 182 return INT_MAX; 183 184 if (cwnd < -2097152) /* -2^21 cubed is long min */ 185 return smss; 186 187 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 188 cwnd *= (cwnd * cwnd); 189 190 /* 191 * C(t - K)^3 + wmax 192 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 193 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 194 * and an extra from multiplying through by CUBIC_C_FACTOR. 195 * 196 * The original formula was this: 197 * cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax; 198 * 199 * CUBIC_C_FACTOR and smss factors were moved up to an earlier 200 * calculation to simplify overflow and underflow detection. 201 */ 202 cwnd = (cwnd >> CUBIC_SHIFT_4) + wmax; 203 204 if (cwnd < 0) 205 return 1; 206 207 return ((unsigned long)cwnd); 208 } 209 210 /* 211 * Compute an approximation of the NewReno cwnd some number of ticks after a 212 * congestion event. RTT should be the average RTT estimate for the path 213 * measured over the previous congestion epoch and wmax is the value of cwnd at 214 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is 215 * rather tricky to understand and it turns out this function is not required. 216 * It is left here for reference. 217 */ 218 static __inline unsigned long 219 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 220 uint32_t smss) 221 { 222 223 /* 224 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT 225 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in 226 * bytes, we have to multiply by smss. 227 */ 228 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) 229 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); 230 } 231 232 /* 233 * Compute an approximation of the "TCP friendly" cwnd some number of ticks 234 * after a congestion event that is designed to yield the same average cwnd as 235 * NewReno while using CUBIC's beta of 0.8. RTT should be the average RTT 236 * estimate for the path measured over the previous congestion epoch and wmax is 237 * the value of cwnd at the last congestion event. 238 */ 239 static __inline unsigned long 240 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 241 uint32_t smss) 242 { 243 244 /* Equation 4 of I-D. */ 245 return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong * 246 smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT); 247 } 248 249 #endif /* _NETINET_CC_CUBIC_H_ */ 250