1 /*-
2 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
3 * Copyright (c) 2010 The FreeBSD Foundation
4 * All rights reserved.
5 *
6 * This software was developed by Lawrence Stewart while studying at the Centre
7 * for Advanced Internet Architectures, Swinburne University of Technology, made
8 * possible in part by a grant from the Cisco University Research Program Fund
9 * at Community Foundation Silicon Valley.
10 *
11 * Portions of this software were developed at the Centre for Advanced
12 * Internet Architectures, Swinburne University of Technology, Melbourne,
13 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
14 *
15 * Redistribution and use in source and binary forms, with or without
16 * modification, are permitted provided that the following conditions
17 * are met:
18 * 1. Redistributions of source code must retain the above copyright
19 * notice, this list of conditions and the following disclaimer.
20 * 2. Redistributions in binary form must reproduce the above copyright
21 * notice, this list of conditions and the following disclaimer in the
22 * documentation and/or other materials provided with the distribution.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * $FreeBSD: releng/10.3/sys/netinet/cc/cc_cubic.h 220560 2011-04-12 08:13:18Z lstewart $
37 */
38
39 #ifndef _NETINET_CC_CUBIC_H_
40 #define _NETINET_CC_CUBIC_H_
41
42 /* Number of bits of precision for fixed point math calcs. */
43 #define CUBIC_SHIFT 8
44
45 #define CUBIC_SHIFT_4 32
46
47 /* 0.5 << CUBIC_SHIFT. */
48 #define RENO_BETA 128
49
50 /* ~0.8 << CUBIC_SHIFT. */
51 #define CUBIC_BETA 204
52
53 /* ~0.2 << CUBIC_SHIFT. */
54 #define ONE_SUB_CUBIC_BETA 51
55
56 /* 3 * ONE_SUB_CUBIC_BETA. */
57 #define THREE_X_PT2 153
58
59 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
60 #define TWO_SUB_PT2 461
61
62 /* ~0.4 << CUBIC_SHIFT. */
63 #define CUBIC_C_FACTOR 102
64
65 /* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */
66 #define CUBIC_FC_FACTOR 230
67
68 /* Don't trust s_rtt until this many rtt samples have been taken. */
69 #define CUBIC_MIN_RTT_SAMPLES 8
70
71 /* Userland only bits. */
72 #ifndef _KERNEL
73
74 extern int hz;
75
76 /*
77 * Implementation based on the formulae found in the CUBIC Internet Draft
78 * "draft-rhee-tcpm-cubic-02".
79 *
80 * Note BETA used in cc_cubic is equal to (1-beta) in the I-D
81 */
82
83 static __inline float
84 theoretical_cubic_k(double wmax_pkts)
85 {
86 double C;
87
88 C = 0.4;
89
90 return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
91 }
92
93 static __inline unsigned long
94 theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss)
95 {
96 double C, wmax_pkts;
97
98 C = 0.4;
99 wmax_pkts = wmax / (double)smss;
100
101 return (smss * (wmax_pkts +
102 (C * pow(ticks_since_cong / (double)hz -
103 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
104 }
105
106 static __inline unsigned long
107 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
108 uint32_t smss)
109 {
110
111 return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
112 }
113
114 static __inline unsigned long
115 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
116 uint32_t smss)
117 {
118
119 return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) *
120 (ticks_since_cong / (float)rtt_ticks) * smss));
121 }
122
123 #endif /* !_KERNEL */
124
125 /*
126 * Compute the CUBIC K value used in the cwnd calculation, using an
127 * implementation of eqn 2 in the I-D. The method used
128 * here is adapted from Apple Computer Technical Report #KT-32.
129 */
130 static __inline int64_t
131 cubic_k(unsigned long wmax_pkts)
132 {
133 int64_t s, K;
134 uint16_t p;
135
136 K = s = 0;
137 p = 0;
138
139 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
140 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
141
142 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
143 while (s >= 256) {
144 s >>= 3;
145 p++;
146 }
147
148 /*
149 * Some magic constants taken from the Apple TR with appropriate
150 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
151 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
152 */
153 K = (((s * 275) >> CUBIC_SHIFT) + 98) -
154 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
155
156 /* Multiply by 2^p to undo the rebasing of s from above. */
157 return (K <<= p);
158 }
159
160 /*
161 * Compute the new cwnd value using an implementation of eqn 1 from the I-D.
162 * Thanks to Kip Macy for help debugging this function.
163 *
164 * XXXLAS: Characterise bounds for overflow.
165 */
166 static __inline unsigned long
167 cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
168 {
169 int64_t cwnd;
170
171 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */
172
173 /* t - K, with CUBIC_SHIFT worth of precision. */
174 cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
175
176 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
177 cwnd *= (cwnd * cwnd);
178
179 /*
180 * C(t - K)^3 + wmax
181 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
182 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
183 * and an extra from multiplying through by CUBIC_C_FACTOR.
184 */
185 cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
186
187 return ((unsigned long)cwnd);
188 }
189
190 /*
191 * Compute an approximation of the NewReno cwnd some number of ticks after a
192 * congestion event. RTT should be the average RTT estimate for the path
193 * measured over the previous congestion epoch and wmax is the value of cwnd at
194 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
195 * rather tricky to understand and it turns out this function is not required.
196 * It is left here for reference.
197 */
198 static __inline unsigned long
199 reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
200 uint32_t smss)
201 {
202
203 /*
204 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT
205 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in
206 * bytes, we have to multiply by smss.
207 */
208 return (((wmax * RENO_BETA) + (((ticks_since_cong * smss)
209 << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT);
210 }
211
212 /*
213 * Compute an approximation of the "TCP friendly" cwnd some number of ticks
214 * after a congestion event that is designed to yield the same average cwnd as
215 * NewReno while using CUBIC's beta of 0.8. RTT should be the average RTT
216 * estimate for the path measured over the previous congestion epoch and wmax is
217 * the value of cwnd at the last congestion event.
218 */
219 static __inline unsigned long
220 tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
221 uint32_t smss)
222 {
223
224 /* Equation 4 of I-D. */
225 return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong *
226 smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT);
227 }
228
229 #endif /* _NETINET_CC_CUBIC_H_ */
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