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 /* 76 * (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor 77 * and taking cube-root yields 448845 as the effective useful limit 78 */ 79 #define CUBED_ROOT_MAX_ULONG 448845 80 81 /* Userland only bits. */ 82 #ifndef _KERNEL 83 84 extern int hz; 85 86 /* 87 * Implementation based on the formulae found in the CUBIC Internet Draft 88 * "draft-ietf-tcpm-cubic-04". 89 * 90 */ 91 92 static __inline float 93 theoretical_cubic_k(double wmax_pkts) 94 { 95 double C; 96 97 C = 0.4; 98 99 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 100 } 101 102 static __inline unsigned long 103 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) 104 { 105 double C, wmax_pkts; 106 107 C = 0.4; 108 wmax_pkts = wmax / (double)smss; 109 110 return (smss * (wmax_pkts + 111 (C * pow(ticks_since_cong / (double)hz - 112 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 113 } 114 115 static __inline unsigned long 116 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 117 uint32_t smss) 118 { 119 120 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 121 } 122 123 static __inline unsigned long 124 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 125 uint32_t smss) 126 { 127 128 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) * 129 (ticks_since_cong / (float)rtt_ticks) * smss)); 130 } 131 132 #endif /* !_KERNEL */ 133 134 /* 135 * Compute the CUBIC K value used in the cwnd calculation, using an 136 * implementation of eqn 2 in the I-D. The method used 137 * here is adapted from Apple Computer Technical Report #KT-32. 138 */ 139 static __inline int64_t 140 cubic_k(unsigned long wmax_pkts) 141 { 142 int64_t s, K; 143 uint16_t p; 144 145 K = s = 0; 146 p = 0; 147 148 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 149 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 150 151 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 152 while (s >= 256) { 153 s >>= 3; 154 p++; 155 } 156 157 /* 158 * Some magic constants taken from the Apple TR with appropriate 159 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 160 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 161 */ 162 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 163 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 164 165 /* Multiply by 2^p to undo the rebasing of s from above. */ 166 return (K <<= p); 167 } 168 169 /* 170 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 171 * Thanks to Kip Macy for help debugging this function. 172 * 173 * XXXLAS: Characterise bounds for overflow. 174 */ 175 static __inline unsigned long 176 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) 177 { 178 int64_t cwnd; 179 180 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ 181 182 /* t - K, with CUBIC_SHIFT worth of precision. */ 183 cwnd = (((int64_t)ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; 184 185 if (cwnd > CUBED_ROOT_MAX_ULONG) 186 return INT_MAX; 187 if (cwnd < -CUBED_ROOT_MAX_ULONG) 188 return 0; 189 190 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 191 cwnd *= (cwnd * cwnd); 192 193 /* 194 * C(t - K)^3 + wmax 195 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 196 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 197 * and an extra from multiplying through by CUBIC_C_FACTOR. 198 */ 199 200 cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax; 201 202 /* 203 * for negative cwnd, limiting to zero as lower bound 204 */ 205 return (lmax(0,cwnd)); 206 } 207 208 /* 209 * Compute an approximation of the NewReno cwnd some number of ticks after a 210 * congestion event. RTT should be the average RTT estimate for the path 211 * measured over the previous congestion epoch and wmax is the value of cwnd at 212 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is 213 * rather tricky to understand and it turns out this function is not required. 214 * It is left here for reference. 215 */ 216 static __inline unsigned long 217 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 218 uint32_t smss) 219 { 220 221 /* 222 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT 223 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in 224 * bytes, we have to multiply by smss. 225 */ 226 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) 227 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); 228 } 229 230 /* 231 * Compute an approximation of the "TCP friendly" cwnd some number of ticks 232 * after a congestion event that is designed to yield the same average cwnd as 233 * NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT 234 * estimate for the path measured over the previous congestion epoch and wmax is 235 * the value of cwnd at the last congestion event. 236 */ 237 static __inline unsigned long 238 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 239 uint32_t smss) 240 { 241 242 /* Equation 4 of I-D. */ 243 return (((wmax * CUBIC_BETA) + 244 (((THREE_X_PT3 * (unsigned long)ticks_since_cong * 245 (unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_ticks))) 246 >> CUBIC_SHIFT); 247 } 248 249 #endif /* _NETINET_CC_CUBIC_H_ */ 250