1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 39 #ifndef _NETINET_CC_CUBIC_H_ 40 #define _NETINET_CC_CUBIC_H_ 41 42 #include <sys/limits.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 /* ~0.7 << CUBIC_SHIFT. */ 53 #define CUBIC_BETA 179 54 55 /* ~0.3 << CUBIC_SHIFT. */ 56 #define ONE_SUB_CUBIC_BETA 77 57 58 /* 3 * ONE_SUB_CUBIC_BETA. */ 59 #define THREE_X_PT3 231 60 61 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ 62 #define TWO_SUB_PT3 435 63 64 /* ~0.4 << CUBIC_SHIFT. */ 65 #define CUBIC_C_FACTOR 102 66 67 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */ 68 #define CUBIC_FC_FACTOR 217 69 70 /* Don't trust s_rtt until this many rtt samples have been taken. */ 71 #define CUBIC_MIN_RTT_SAMPLES 8 72 73 /* 74 * (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor 75 * and taking cube-root yields 448845 as the effective useful limit 76 */ 77 #define CUBED_ROOT_MAX_ULONG 448845 78 79 /* Flags used in the cubic structure */ 80 #define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */ 81 #define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */ 82 #define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */ 83 #define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */ 84 #define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */ 85 #define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */ 86 #define CUBICFLAG_IN_TF 0x00000040 /* We are in TCP friendly region */ 87 88 /* Kernel only bits */ 89 #ifdef _KERNEL 90 struct cubic { 91 /* CUBIC K in fixed point form with CUBIC_SHIFT worth of precision. */ 92 int64_t K; 93 /* Sum of RTT samples across an epoch in usecs. */ 94 int64_t sum_rtt_usecs; 95 /* Size of cwnd just before cwnd was reduced in the last congestion event */ 96 uint64_t W_max; 97 /* The cwnd at the beginning of the current congestion avoidance stage */ 98 uint64_t cwnd_epoch; 99 /* various flags */ 100 uint32_t flags; 101 /* Minimum observed rtt in usecs. */ 102 int min_rtt_usecs; 103 /* Mean observed rtt between congestion epochs. */ 104 int mean_rtt_usecs; 105 /* ACKs since last congestion event. */ 106 int epoch_ack_count; 107 /* Timestamp (in ticks) at which the current CA epoch started. */ 108 int t_epoch; 109 /* Timestamp (in ticks) at which the previous CA epoch started. */ 110 int undo_t_epoch; 111 /* Few variables to restore the state after RTO_ERR */ 112 int64_t undo_K; 113 uint64_t undo_W_max; 114 uint64_t undo_cwnd_epoch; 115 uint32_t css_baseline_minrtt; 116 uint32_t css_current_round_minrtt; 117 uint32_t css_lastround_minrtt; 118 uint32_t css_rttsample_count; 119 uint32_t css_entered_at_round; 120 uint32_t css_current_round; 121 uint32_t css_fas_at_css_entry; 122 uint32_t css_lowrtt_fas; 123 uint32_t css_last_fas; 124 }; 125 #endif 126 127 /* Userland only bits. */ 128 #ifndef _KERNEL 129 130 extern int hz; 131 132 /* 133 * Implementation based on the formulae found in the CUBIC Internet Draft 134 * "draft-ietf-tcpm-cubic-04". 135 * 136 */ 137 138 static __inline float 139 theoretical_cubic_k(double wmax_pkts) 140 { 141 double C; 142 143 C = 0.4; 144 145 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); 146 } 147 148 static __inline unsigned long 149 theoretical_cubic_cwnd(int ticks_since_epoch, unsigned long wmax, uint32_t smss) 150 { 151 double C, wmax_pkts; 152 153 C = 0.4; 154 wmax_pkts = wmax / (double)smss; 155 156 return (smss * (wmax_pkts + 157 (C * pow(ticks_since_epoch / (double)hz - 158 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); 159 } 160 161 static __inline unsigned long 162 theoretical_reno_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax, 163 uint32_t smss) 164 { 165 166 return ((wmax * 0.5) + ((ticks_since_epoch / (float)rtt_ticks) * smss)); 167 } 168 169 static __inline unsigned long 170 theoretical_tf_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax, 171 uint32_t smss) 172 { 173 174 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) * 175 (ticks_since_epoch / (float)rtt_ticks) * smss)); 176 } 177 178 #endif /* !_KERNEL */ 179 180 /* 181 * Compute the CUBIC K value used in the cwnd calculation, using an 182 * implementation of eqn 2 in the I-D. The method used 183 * here is adapted from Apple Computer Technical Report #KT-32. 184 */ 185 static __inline int64_t 186 cubic_k(unsigned long wmax_pkts) 187 { 188 int64_t s, K; 189 uint16_t p; 190 191 K = s = 0; 192 p = 0; 193 194 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ 195 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; 196 197 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ 198 while (s >= 256) { 199 s >>= 3; 200 p++; 201 } 202 203 /* 204 * Some magic constants taken from the Apple TR with appropriate 205 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << 206 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. 207 */ 208 K = (((s * 275) >> CUBIC_SHIFT) + 98) - 209 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); 210 211 /* Multiply by 2^p to undo the rebasing of s from above. */ 212 return (K <<= p); 213 } 214 215 /* 216 * Compute the new cwnd value using an implementation of eqn 1 from the I-D. 217 * Thanks to Kip Macy for help debugging this function. 218 * 219 * XXXLAS: Characterise bounds for overflow. 220 */ 221 static __inline unsigned long 222 cubic_cwnd(int usecs_since_epoch, unsigned long wmax, uint32_t smss, int64_t K) 223 { 224 int64_t cwnd; 225 226 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ 227 228 /* t - K, with CUBIC_SHIFT worth of precision. */ 229 cwnd = (((int64_t)usecs_since_epoch << CUBIC_SHIFT) - (K * hz * tick)) / 230 (hz * tick); 231 232 if (cwnd > CUBED_ROOT_MAX_ULONG) 233 return INT_MAX; 234 if (cwnd < -CUBED_ROOT_MAX_ULONG) 235 return 0; 236 237 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ 238 cwnd *= (cwnd * cwnd); 239 240 /* 241 * C(t - K)^3 + wmax 242 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of 243 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, 244 * and an extra from multiplying through by CUBIC_C_FACTOR. 245 */ 246 247 cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax; 248 249 /* 250 * for negative cwnd, limiting to zero as lower bound 251 */ 252 return (lmax(0,cwnd)); 253 } 254 255 /* 256 * Compute an approximation of the NewReno cwnd some number of usecs after a 257 * congestion event. RTT should be the average RTT estimate for the path 258 * measured over the previous congestion epoch and wmax is the value of cwnd at 259 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is 260 * rather tricky to understand and it turns out this function is not required. 261 * It is left here for reference. 262 * 263 * XXX: Not used 264 */ 265 static __inline unsigned long 266 reno_cwnd(int usecs_since_epoch, int rtt_usecs, 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) + (((usecs_since_epoch * smss) 276 << CUBIC_SHIFT) / rtt_usecs)) >> CUBIC_SHIFT); 277 } 278 279 /* 280 * Compute the "TCP friendly" cwnd by newreno in congestion avoidance state. 281 */ 282 static __inline unsigned long 283 tf_cwnd(struct cc_var *ccv) 284 { 285 /* newreno is "TCP friendly" */ 286 return newreno_cc_cwnd_in_cong_avoid(ccv); 287 } 288 289 #endif /* _NETINET_CC_CUBIC_H_ */ 290