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 *
7 * This software was developed by Lawrence Stewart while studying at the Centre
8 * for Advanced Internet Architectures, Swinburne University of Technology, made
9 * possible in part by a grant from the Cisco University Research Program Fund
10 * at Community Foundation Silicon Valley.
11 *
12 * Portions of this software were developed at the Centre for Advanced
13 * Internet Architectures, Swinburne University of Technology, Melbourne,
14 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
15 *
16 * Redistribution and use in source and binary forms, with or without
17 * modification, are permitted provided that the following conditions
18 * are met:
19 * 1. Redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer.
21 * 2. Redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 *
37 * $FreeBSD$
38 */
39
40 #ifndef _NETINET_CC_CUBIC_H_
41 #define _NETINET_CC_CUBIC_H_
42
43 /* Number of bits of precision for fixed point math calcs. */
44 #define CUBIC_SHIFT 8
45
46 #define CUBIC_SHIFT_4 32
47
48 /* 0.5 << CUBIC_SHIFT. */
49 #define RENO_BETA 128
50
51 /* ~0.8 << CUBIC_SHIFT. */
52 #define CUBIC_BETA 204
53
54 /* ~0.2 << CUBIC_SHIFT. */
55 #define ONE_SUB_CUBIC_BETA 51
56
57 /* 3 * ONE_SUB_CUBIC_BETA. */
58 #define THREE_X_PT2 153
59
60 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
61 #define TWO_SUB_PT2 461
62
63 /* ~0.4 << CUBIC_SHIFT. */
64 #define CUBIC_C_FACTOR 102
65
66 /* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */
67 #define CUBIC_FC_FACTOR 230
68
69 /* Don't trust s_rtt until this many rtt samples have been taken. */
70 #define CUBIC_MIN_RTT_SAMPLES 8
71
72 /* Userland only bits. */
73 #ifndef _KERNEL
74
75 extern int hz;
76
77 /*
78 * Implementation based on the formulae found in the CUBIC Internet Draft
79 * "draft-rhee-tcpm-cubic-02".
80 *
81 * Note BETA used in cc_cubic is equal to (1-beta) in the I-D
82 */
83
84 static __inline float
85 theoretical_cubic_k(double wmax_pkts)
86 {
87 double C;
88
89 C = 0.4;
90
91 return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
92 }
93
94 static __inline uint32_t
95 theoretical_cubic_cwnd(int ticks_since_cong, uint32_t wmax, uint32_t smss)
96 {
97 double C, wmax_pkts;
98
99 C = 0.4;
100 wmax_pkts = wmax / (double)smss;
101
102 return (smss * (wmax_pkts +
103 (C * pow(ticks_since_cong / (double)hz -
104 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
105 }
106
107 static __inline uint32_t
108 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, uint32_t wmax,
109 uint32_t smss)
110 {
111
112 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
113 }
114
115 static __inline uint32_t
116 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
117 uint32_t smss)
118 {
119
120 return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) *
121 (ticks_since_cong / (float)rtt_ticks) * smss));
122 }
123
124 #endif /* !_KERNEL */
125
126 /*
127 * Compute the CUBIC K value used in the cwnd calculation, using an
128 * implementation of eqn 2 in the I-D. The method used
129 * here is adapted from Apple Computer Technical Report #KT-32.
130 */
131 static __inline int64_t
132 cubic_k(uint32_t wmax_pkts)
133 {
134 int64_t s, K;
135 uint16_t p;
136
137 K = s = 0;
138 p = 0;
139
140 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
141 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
142
143 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
144 while (s >= 256) {
145 s >>= 3;
146 p++;
147 }
148
149 /*
150 * Some magic constants taken from the Apple TR with appropriate
151 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
152 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
153 */
154 K = (((s * 275) >> CUBIC_SHIFT) + 98) -
155 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
156
157 /* Multiply by 2^p to undo the rebasing of s from above. */
158 return (K <<= p);
159 }
160
161 /*
162 * Compute the new cwnd value using an implementation of eqn 1 from the I-D.
163 * Thanks to Kip Macy for help debugging this function.
164 *
165 * XXXLAS: Characterise bounds for overflow.
166 */
167 static __inline uint32_t
168 cubic_cwnd(int ticks_since_cong, uint32_t 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 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
178 cwnd *= (cwnd * cwnd);
179
180 /*
181 * C(t - K)^3 + wmax
182 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
183 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
184 * and an extra from multiplying through by CUBIC_C_FACTOR.
185 */
186 cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
187
188 return ((uint32_t)cwnd);
189 }
190
191 /*
192 * Compute an approximation of the "TCP friendly" cwnd some number of ticks
193 * after a congestion event that is designed to yield the same average cwnd as
194 * NewReno while using CUBIC's beta of 0.8. RTT should be the average RTT
195 * estimate for the path measured over the previous congestion epoch and wmax is
196 * the value of cwnd at the last congestion event.
197 */
198 static __inline uint32_t
199 tf_cwnd(int ticks_since_cong, int rtt_ticks, uint32_t wmax,
200 uint32_t smss)
201 {
202
203 /* Equation 4 of I-D. */
204 return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong *
205 smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT);
206 }
207
208 #endif /* _NETINET_CC_CUBIC_H_ */