1 /* 2 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org> 3 * Copyright (c) 2010 The FreeBSD Foundation 4 * All rights reserved. 5 * Copyright (c) 2017 by Delphix. All rights reserved. 6 * Copyright 2019 Joyent, Inc. 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 /* ~0.8 << CUBIC_SHIFT. */ 53 #define CUBIC_BETA 204 54 55 /* ~0.2 << CUBIC_SHIFT. */ 56 #define ONE_SUB_CUBIC_BETA 51 57 58 /* 3 * ONE_SUB_CUBIC_BETA. */ 59 #define THREE_X_PT2 153 60 61 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ 62 #define TWO_SUB_PT2 461 63 64 /* ~0.4 << CUBIC_SHIFT. */ 65 #define CUBIC_C_FACTOR 102 66 67 /* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */ 68 #define CUBIC_FC_FACTOR 230 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-rhee-tcpm-cubic-02". 81 * 82 * Note BETA used in cc_cubic is equal to (1-beta) in the I-D 83 */ 84 85 static __inline float 86 theoretical_cubic_k(double wmax_pkts) 87 { 88 double C; 89 90 C = 0.4; 91 92 return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 93 } 94 95 static __inline uint32_t 96 theoretical_cubic_cwnd(int ticks_since_cong, uint32_t wmax, uint32_t smss) 97 { 98 double C, wmax_pkts; 99 100 C = 0.4; 101 wmax_pkts = wmax / (double)smss; 102 103 return (smss * (wmax_pkts + 104 (C * pow(ticks_since_cong / (double)hz - 105 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 106 } 107 108 static __inline uint32_t 109 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, uint32_t wmax, 110 uint32_t smss) 111 { 112 113 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 114 } 115 116 static __inline uint32_t 117 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 118 uint32_t smss) 119 { 120 121 return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) * 122 (ticks_since_cong / (float)rtt_ticks) * smss)); 123 } 124 125 #endif /* !_KERNEL */ 126 127 /* 128 * Compute the CUBIC K value used in the cwnd calculation, using an 129 * implementation of eqn 2 in the I-D. The method used 130 * here is adapted from Apple Computer Technical Report #KT-32. 131 */ 132 static __inline int64_t 133 cubic_k(uint32_t wmax_pkts) 134 { 135 int64_t s, K; 136 uint16_t p; 137 138 K = s = 0; 139 p = 0; 140 141 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 142 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 143 144 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 145 while (s >= 256) { 146 s >>= 3; 147 p++; 148 } 149 150 /* 151 * Some magic constants taken from the Apple TR with appropriate 152 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 153 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 154 */ 155 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 156 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 157 158 /* Multiply by 2^p to undo the rebasing of s from above. */ 159 return (K <<= p); 160 } 161 162 /* 163 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 164 * Thanks to Kip Macy for help debugging this function. 165 * 166 * XXXLAS: Characterise bounds for overflow. 167 */ 168 static __inline uint32_t 169 cubic_cwnd(hrtime_t nsecs_since_cong, uint32_t wmax, uint32_t smss, int64_t K) 170 { 171 int64_t t, cwnd; 172 173 /* 174 * Convert nsecs_since_cong to milliseconds, with CUBIC_SHIFT worth 175 * of precision. 176 */ 177 t = NSEC2MSEC(nsecs_since_cong << CUBIC_SHIFT); 178 179 /* 180 * K is the time period in seconds that it will take to reach wmax. The 181 * value is kept in fixed point form with CUBIC_SHIFT worth of 182 * precision. 183 * 184 * For comparison with t, we convert K to milliseconds, and then convert 185 * the result back to seconds. 186 * 187 * cwnd = t - K, with CUBIC_SHIFT worth of precision. 188 */ 189 cwnd = (t - K * MILLISEC) / MILLISEC; 190 191 /* cwnd = (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 192 cwnd *= (cwnd * cwnd); 193 194 /* 195 * C(t - K)^3 + wmax 196 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 197 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 198 * and an extra from multiplying through by CUBIC_C_FACTOR. 199 */ 200 cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax; 201 202 return ((uint32_t)cwnd); 203 } 204 205 /* 206 * Compute an approximation of the "TCP friendly" cwnd some number of 207 * nanoseconds after a congestion event that is designed to yield the same 208 * average cwnd as NewReno while using CUBIC's beta of 0.8. RTT should be the 209 * average RTT estimate for the path measured over the previous congestion 210 * epoch and wmax is the value of cwnd at the last congestion event. 211 */ 212 static __inline uint32_t 213 tf_cwnd(hrtime_t nsecs_since_cong, hrtime_t rtt_nsecs, uint32_t wmax, 214 uint32_t smss) 215 { 216 217 /* Equation 4 of I-D. */ 218 return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * nsecs_since_cong * 219 smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_nsecs)) >> CUBIC_SHIFT); 220 } 221 222 #endif /* _NETINET_CC_CUBIC_H_ */ 223