xref: /illumos-gate/usr/src/uts/common/inet/cc/cc_cubic.h (revision 3b0b0a4e9ef34199357e064b48f2dd2e9ff1c9a2)
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  * Copyright 2020 RackTop Systems, Inc.
8  *
9  * This software was developed by Lawrence Stewart while studying at the Centre
10  * for Advanced Internet Architectures, Swinburne University of Technology, made
11  * possible in part by a grant from the Cisco University Research Program Fund
12  * at Community Foundation Silicon Valley.
13  *
14  * Portions of this software were developed at the Centre for Advanced
15  * Internet Architectures, Swinburne University of Technology, Melbourne,
16  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
17  *
18  * Redistribution and use in source and binary forms, with or without
19  * modification, are permitted provided that the following conditions
20  * are met:
21  * 1. Redistributions of source code must retain the above copyright
22  *    notice, this list of conditions and the following disclaimer.
23  * 2. Redistributions in binary form must reproduce the above copyright
24  *    notice, this list of conditions and the following disclaimer in the
25  *    documentation and/or other materials provided with the distribution.
26  *
27  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
30  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37  * SUCH DAMAGE.
38  *
39  * $FreeBSD$
40  */
41 
42 #ifndef _NETINET_CC_CUBIC_H_
43 #define	_NETINET_CC_CUBIC_H_
44 
45 /* Number of bits of precision for fixed point math calcs. */
46 #define	CUBIC_SHIFT		8
47 
48 #define	CUBIC_SHIFT_4		32
49 
50 /* 0.5 << CUBIC_SHIFT. */
51 #define	RENO_BETA		128
52 
53 /* ~0.8 << CUBIC_SHIFT. */
54 #define	CUBIC_BETA		204
55 
56 /* ~0.2 << CUBIC_SHIFT. */
57 #define	ONE_SUB_CUBIC_BETA	51
58 
59 /* 3 * ONE_SUB_CUBIC_BETA. */
60 #define	THREE_X_PT2		153
61 
62 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
63 #define	TWO_SUB_PT2		461
64 
65 /* ~0.4 << CUBIC_SHIFT. */
66 #define	CUBIC_C_FACTOR		102
67 
68 /* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */
69 #define	CUBIC_FC_FACTOR		230
70 
71 /* Don't trust s_rtt until this many rtt samples have been taken. */
72 #define	CUBIC_MIN_RTT_SAMPLES	8
73 
74 /*
75  * (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor
76  * and taking cube-root yields 448845 as the effective useful limit
77  */
78 #define	CUBED_ROOT_MAX_ULONG	448845
79 
80 /* Userland only bits. */
81 #ifndef _KERNEL
82 
83 extern int hz;
84 
85 /*
86  * Implementation based on the formulae found in the CUBIC Internet Draft
87  * "draft-rhee-tcpm-cubic-02".
88  *
89  * Note BETA used in cc_cubic is equal to (1-beta) in the I-D
90  */
91 
92 static __inline float
theoretical_cubic_k(double wmax_pkts)93 theoretical_cubic_k(double wmax_pkts)
94 {
95 	double C;
96 
97 	C = 0.4;
98 
99 	return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
100 }
101 
102 static __inline uint32_t
theoretical_cubic_cwnd(int ticks_since_cong,uint32_t wmax,uint32_t smss)103 theoretical_cubic_cwnd(int ticks_since_cong, uint32_t wmax, uint32_t smss)
104 {
105 	double C, wmax_pkts;
106 
107 	C = 0.4;
108 	wmax_pkts = wmax / (double)smss;
109 
110 	return (smss * (wmax_pkts +
111 	    (C * pow(ticks_since_cong / (double)hz -
112 	    theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
113 }
114 
115 static __inline uint32_t
theoretical_reno_cwnd(int ticks_since_cong,int rtt_ticks,uint32_t wmax,uint32_t smss)116 theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, uint32_t wmax,
117     uint32_t smss)
118 {
119 
120 	return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
121 }
122 
123 static __inline uint32_t
theoretical_tf_cwnd(int ticks_since_cong,int rtt_ticks,unsigned long wmax,uint32_t smss)124 theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
125     uint32_t smss)
126 {
127 
128 	return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) *
129 	    (ticks_since_cong / (float)rtt_ticks) * smss));
130 }
131 
132 #endif /* !_KERNEL */
133 
134 /*
135  * Compute the CUBIC K value used in the cwnd calculation, using an
136  * implementation of eqn 2 in the I-D. The method used
137  * here is adapted from Apple Computer Technical Report #KT-32.
138  */
139 static __inline int64_t
cubic_k(uint32_t wmax_pkts)140 cubic_k(uint32_t wmax_pkts)
141 {
142 	int64_t s, K;
143 	uint16_t p;
144 
145 	K = s = 0;
146 	p = 0;
147 
148 	/* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
149 	s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
150 
151 	/* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
152 	while (s >= 256) {
153 		s >>= 3;
154 		p++;
155 	}
156 
157 	/*
158 	 * Some magic constants taken from the Apple TR with appropriate
159 	 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
160 	 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
161 	 */
162 	K = (((s * 275) >> CUBIC_SHIFT) + 98) -
163 	    (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
164 
165 	/* Multiply by 2^p to undo the rebasing of s from above. */
166 	return (K <<= p);
167 }
168 
169 /*
170  * Compute the new cwnd value using an implementation of eqn 1 from the I-D.
171  * Thanks to Kip Macy for help debugging this function.
172  *
173  * XXXLAS: Characterise bounds for overflow.
174  */
175 static __inline uint32_t
cubic_cwnd(hrtime_t nsecs_since_cong,uint32_t wmax,uint32_t smss,int64_t K)176 cubic_cwnd(hrtime_t nsecs_since_cong, uint32_t wmax, uint32_t smss, int64_t K)
177 {
178 	int64_t t, cwnd;
179 
180 	/*
181 	 * Convert nsecs_since_cong to milliseconds, with CUBIC_SHIFT worth
182 	 * of precision.
183 	 */
184 	t = NSEC2MSEC(nsecs_since_cong << CUBIC_SHIFT);
185 
186 	/*
187 	 * K is the time period in seconds that it will take to reach wmax. The
188 	 * value is kept in fixed point form with CUBIC_SHIFT worth of
189 	 * precision.
190 	 *
191 	 * For comparison with t, we convert K to milliseconds, and then convert
192 	 * the result back to seconds.
193 	 *
194 	 * cwnd = t - K, with CUBIC_SHIFT worth of precision.
195 	 */
196 	cwnd = (t - K * MILLISEC) / MILLISEC;
197 
198 	if (cwnd > CUBED_ROOT_MAX_ULONG)
199 		return (INT_MAX);
200 	if (cwnd < -CUBED_ROOT_MAX_ULONG)
201 		return (0);
202 
203 	/* cwnd = (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
204 	cwnd *= (cwnd * cwnd);
205 
206 	/*
207 	 * C(t - K)^3 + wmax
208 	 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
209 	 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
210 	 * and an extra from multiplying through by CUBIC_C_FACTOR.
211 	 */
212 	cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
213 
214 	/*
215 	 * for negative cwnd, limiting to zero as lower bound
216 	 */
217 	return (max(0, cwnd));
218 }
219 
220 /*
221  * Compute an approximation of the "TCP friendly" cwnd some number of
222  * nanoseconds after a congestion event that is designed to yield the same
223  * average cwnd as NewReno while using CUBIC's beta of 0.8. RTT should be the
224  * average RTT estimate for the path measured over the previous congestion
225  * epoch and wmax is the value of cwnd at the last congestion event.
226  */
227 static __inline uint32_t
tf_cwnd(hrtime_t nsecs_since_cong,hrtime_t rtt_nsecs,uint32_t wmax,uint32_t smss)228 tf_cwnd(hrtime_t nsecs_since_cong, hrtime_t rtt_nsecs, uint32_t wmax,
229     uint32_t smss)
230 {
231 
232 	/* Equation 4 of I-D. */
233 	return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * nsecs_since_cong *
234 	    smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_nsecs)) >> CUBIC_SHIFT);
235 }
236 
237 #endif /* _NETINET_CC_CUBIC_H_ */
238