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 /* Flags used in the cubic structure */ 82 #define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */ 83 #define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */ 84 #define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */ 85 #define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */ 86 #define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */ 87 #define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */ 88 89 /* Kernel only bits */ 90 #ifdef _KERNEL 91 struct cubic { 92 /* Cubic K in fixed point form with CUBIC_SHIFT worth of precision. */ 93 int64_t K; 94 /* Sum of RTT samples across an epoch in ticks. */ 95 int64_t sum_rtt_ticks; 96 /* cwnd at the most recent congestion event. */ 97 unsigned long max_cwnd; 98 /* cwnd at the previous congestion event. */ 99 unsigned long prev_max_cwnd; 100 /* A copy of prev_max_cwnd. Used for CC_RTO_ERR */ 101 unsigned long prev_max_cwnd_cp; 102 /* various flags */ 103 uint32_t flags; 104 /* Minimum observed rtt in ticks. */ 105 int min_rtt_ticks; 106 /* Mean observed rtt between congestion epochs. */ 107 int mean_rtt_ticks; 108 /* ACKs since last congestion event. */ 109 int epoch_ack_count; 110 /* Timestamp (in ticks) of arriving in congestion avoidance from last 111 * congestion event. 112 */ 113 int t_last_cong; 114 /* Timestamp (in ticks) of a previous congestion event. Used for 115 * CC_RTO_ERR. 116 */ 117 int t_last_cong_prev; 118 uint32_t css_baseline_minrtt; 119 uint32_t css_current_round_minrtt; 120 uint32_t css_lastround_minrtt; 121 uint32_t css_rttsample_count; 122 uint32_t css_entered_at_round; 123 uint32_t css_current_round; 124 uint32_t css_fas_at_css_entry; 125 uint32_t css_lowrtt_fas; 126 uint32_t css_last_fas; 127 }; 128 #endif 129 130 /* Userland only bits. */ 131 #ifndef _KERNEL 132 133 extern int hz; 134 135 /* 136 * Implementation based on the formulae found in the CUBIC Internet Draft 137 * "draft-ietf-tcpm-cubic-04". 138 * 139 */ 140 141 static __inline float 142 theoretical_cubic_k(double wmax_pkts) 143 { 144 double C; 145 146 C = 0.4; 147 148 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 149 } 150 151 static __inline unsigned long 152 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) 153 { 154 double C, wmax_pkts; 155 156 C = 0.4; 157 wmax_pkts = wmax / (double)smss; 158 159 return (smss * (wmax_pkts + 160 (C * pow(ticks_since_cong / (double)hz - 161 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 162 } 163 164 static __inline unsigned long 165 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 166 uint32_t smss) 167 { 168 169 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); 170 } 171 172 static __inline unsigned long 173 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 174 uint32_t smss) 175 { 176 177 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) * 178 (ticks_since_cong / (float)rtt_ticks) * smss)); 179 } 180 181 #endif /* !_KERNEL */ 182 183 /* 184 * Compute the CUBIC K value used in the cwnd calculation, using an 185 * implementation of eqn 2 in the I-D. The method used 186 * here is adapted from Apple Computer Technical Report #KT-32. 187 */ 188 static __inline int64_t 189 cubic_k(unsigned long wmax_pkts) 190 { 191 int64_t s, K; 192 uint16_t p; 193 194 K = s = 0; 195 p = 0; 196 197 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 198 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 199 200 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 201 while (s >= 256) { 202 s >>= 3; 203 p++; 204 } 205 206 /* 207 * Some magic constants taken from the Apple TR with appropriate 208 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 209 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 210 */ 211 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 212 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 213 214 /* Multiply by 2^p to undo the rebasing of s from above. */ 215 return (K <<= p); 216 } 217 218 /* 219 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 220 * Thanks to Kip Macy for help debugging this function. 221 * 222 * XXXLAS: Characterise bounds for overflow. 223 */ 224 static __inline unsigned long 225 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) 226 { 227 int64_t cwnd; 228 229 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ 230 231 /* t - K, with CUBIC_SHIFT worth of precision. */ 232 cwnd = (((int64_t)ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; 233 234 if (cwnd > CUBED_ROOT_MAX_ULONG) 235 return INT_MAX; 236 if (cwnd < -CUBED_ROOT_MAX_ULONG) 237 return 0; 238 239 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 240 cwnd *= (cwnd * cwnd); 241 242 /* 243 * C(t - K)^3 + wmax 244 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 245 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 246 * and an extra from multiplying through by CUBIC_C_FACTOR. 247 */ 248 249 cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax; 250 251 /* 252 * for negative cwnd, limiting to zero as lower bound 253 */ 254 return (lmax(0,cwnd)); 255 } 256 257 /* 258 * Compute an approximation of the NewReno cwnd some number of ticks after a 259 * congestion event. RTT should be the average RTT estimate for the path 260 * measured over the previous congestion epoch and wmax is the value of cwnd at 261 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is 262 * rather tricky to understand and it turns out this function is not required. 263 * It is left here for reference. 264 */ 265 static __inline unsigned long 266 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 267 uint32_t smss) 268 { 269 270 /* 271 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT 272 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in 273 * bytes, we have to multiply by smss. 274 */ 275 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) 276 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); 277 } 278 279 /* 280 * Compute an approximation of the "TCP friendly" cwnd some number of ticks 281 * after a congestion event that is designed to yield the same average cwnd as 282 * NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT 283 * estimate for the path measured over the previous congestion epoch and wmax is 284 * the value of cwnd at the last congestion event. 285 */ 286 static __inline unsigned long 287 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, 288 uint32_t smss) 289 { 290 291 /* Equation 4 of I-D. */ 292 return (((wmax * CUBIC_BETA) + 293 (((THREE_X_PT3 * (unsigned long)ticks_since_cong * 294 (unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_ticks))) 295 >> CUBIC_SHIFT); 296 } 297 298 #endif /* _NETINET_CC_CUBIC_H_ */ 299