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 /* ~0.7 << CUBIC_SHIFT. */ 55 #define CUBIC_BETA 179 56 57 /* ~0.3 << CUBIC_SHIFT. */ 58 #define ONE_SUB_CUBIC_BETA 77 59 60 /* 3 * ONE_SUB_CUBIC_BETA. */ 61 #define THREE_X_PT3 231 62 63 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ 64 #define TWO_SUB_PT3 435 65 66 /* ~0.4 << CUBIC_SHIFT. */ 67 #define CUBIC_C_FACTOR 102 68 69 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */ 70 #define CUBIC_FC_FACTOR 217 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-ietf-tcpm-cubic-04". 83 * 84 */ 85 86 static __inline float 87 theoretical_cubic_k(double wmax_pkts) 88 { 89 double C; 90 91 C = 0.4; 92 93 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 94 } 95 96 static __inline unsigned long 97 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) 98 { 99 double C, wmax_pkts; 100 101 C = 0.4; 102 wmax_pkts = wmax / (double)smss; 103 104 return (smss * (wmax_pkts + 105 (C * pow(ticks_since_cong / (double)hz - 106 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 107 } 108 109 static __inline unsigned long 110 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 111 uint32_t smss) 112 { 113 114 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 115 } 116 117 static __inline unsigned long 118 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 119 uint32_t smss) 120 { 121 122 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) * 123 (ticks_since_cong / (float)rtt_ticks) * smss)); 124 } 125 126 #endif /* !_KERNEL */ 127 128 /* 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. 132 */ 133 static __inline int64_t 134 cubic_k(unsigned long wmax_pkts) 135 { 136 int64_t s, K; 137 uint16_t p; 138 139 K = s = 0; 140 p = 0; 141 142 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 143 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 144 145 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 146 while (s >= 256) { 147 s >>= 3; 148 p++; 149 } 150 151 /* 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. 155 */ 156 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 157 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 158 159 /* Multiply by 2^p to undo the rebasing of s from above. */ 160 return (K <<= p); 161 } 162 163 /* 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. 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 /* moved this calculation up because it cannot overflow or underflow */ 178 cwnd *= CUBIC_C_FACTOR * smss; 179 180 if (cwnd > 2097151) /* 2^21 cubed is long max */ 181 return INT_MAX; 182 183 if (cwnd < -2097152) /* -2^21 cubed is long min */ 184 return smss; 185 186 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 187 cwnd *= (cwnd * cwnd); 188 189 /* 190 * C(t - K)^3 + wmax 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. 194 * 195 * The original formula was this: 196 * cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax; 197 * 198 * CUBIC_C_FACTOR and smss factors were moved up to an earlier 199 * calculation to simplify overflow and underflow detection. 200 */ 201 cwnd = (cwnd >> CUBIC_SHIFT_4) + wmax; 202 203 if (cwnd < 0) 204 return 1; 205 206 return ((unsigned long)cwnd); 207 } 208 209 /* 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. 216 */ 217 static __inline unsigned long 218 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 219 uint32_t smss) 220 { 221 222 /* 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. 226 */ 227 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) 228 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); 229 } 230 231 /* 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. 237 */ 238 static __inline unsigned long 239 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 240 uint32_t smss) 241 { 242 243 /* 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); 246 } 247 248 #endif /* _NETINET_CC_CUBIC_H_ */ 249