2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
5 * Copyright (c) 2010 The FreeBSD Foundation
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.
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.
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
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.
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
41 #ifndef _NETINET_CC_CUBIC_H_
42 #define _NETINET_CC_CUBIC_H_
44 #include <sys/limits.h>
46 /* Number of bits of precision for fixed point math calcs. */
49 #define CUBIC_SHIFT_4 32
51 /* 0.5 << CUBIC_SHIFT. */
54 /* ~0.7 << CUBIC_SHIFT. */
55 #define CUBIC_BETA 179
57 /* ~0.3 << CUBIC_SHIFT. */
58 #define ONE_SUB_CUBIC_BETA 77
60 /* 3 * ONE_SUB_CUBIC_BETA. */
61 #define THREE_X_PT3 231
63 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
64 #define TWO_SUB_PT3 435
66 /* ~0.4 << CUBIC_SHIFT. */
67 #define CUBIC_C_FACTOR 102
69 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */
70 #define CUBIC_FC_FACTOR 217
72 /* Don't trust s_rtt until this many rtt samples have been taken. */
73 #define CUBIC_MIN_RTT_SAMPLES 8
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
79 #define CUBED_ROOT_MAX_ULONG 448845
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 */
89 /* Kernel only bits */
92 /* CUBIC K in fixed point form with CUBIC_SHIFT worth of precision. */
94 /* Sum of RTT samples across an epoch in usecs. */
95 int64_t sum_rtt_usecs;
96 /* Size of cwnd just before cwnd was reduced in the last congestion event */
98 /* An estimate for the congestion window in the Reno-friendly region */
100 /* The cwnd at the beginning of the current congestion avoidance stage */
103 * Size of cwnd at the time of setting ssthresh most recently,
104 * either upon exiting the first slow start, or just before cwnd
105 * was reduced in the last congestion event
110 /* Minimum observed rtt in usecs. */
112 /* Mean observed rtt between congestion epochs. */
114 /* ACKs since last congestion event. */
116 /* Timestamp (in ticks) at which the current CA epoch started. */
118 /* Timestamp (in ticks) at which the previous CA epoch started. */
120 /* Few variables to restore the state after RTO_ERR */
122 uint64_t undo_cwnd_prior;
125 uint64_t undo_cwnd_epoch;
126 /* Number of congestion events experienced */
127 uint64_t num_cong_events;
128 uint32_t css_baseline_minrtt;
129 uint32_t css_current_round_minrtt;
130 uint32_t css_lastround_minrtt;
131 uint32_t css_rttsample_count;
132 uint32_t css_entered_at_round;
133 uint32_t css_current_round;
134 uint32_t css_fas_at_css_entry;
135 uint32_t css_lowrtt_fas;
136 uint32_t css_last_fas;
140 /* Userland only bits. */
146 * Implementation based on the formulae found in the CUBIC Internet Draft
147 * "draft-ietf-tcpm-cubic-04".
151 static __inline float
152 theoretical_cubic_k(double wmax_pkts)
158 return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
161 static __inline unsigned long
162 theoretical_cubic_cwnd(int ticks_since_epoch, unsigned long wmax, uint32_t smss)
167 wmax_pkts = wmax / (double)smss;
169 return (smss * (wmax_pkts +
170 (C * pow(ticks_since_epoch / (double)hz -
171 theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
174 static __inline unsigned long
175 theoretical_reno_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax,
179 return ((wmax * 0.5) + ((ticks_since_epoch / (float)rtt_ticks) * smss));
182 static __inline unsigned long
183 theoretical_tf_cwnd(int ticks_since_epoch, int rtt_ticks, unsigned long wmax,
187 return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) *
188 (ticks_since_epoch / (float)rtt_ticks) * smss));
191 #endif /* !_KERNEL */
194 * Compute the CUBIC K value used in the cwnd calculation, using an
195 * implementation of eqn 2 in the I-D. The method used
196 * here is adapted from Apple Computer Technical Report #KT-32.
198 static __inline int64_t
199 cubic_k(unsigned long wmax_pkts)
207 /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
208 s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
210 /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
217 * Some magic constants taken from the Apple TR with appropriate
218 * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
219 * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
221 K = (((s * 275) >> CUBIC_SHIFT) + 98) -
222 (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
224 /* Multiply by 2^p to undo the rebasing of s from above. */
229 * Compute the new cwnd value using an implementation of eqn 1 from the I-D.
230 * Thanks to Kip Macy for help debugging this function.
232 * XXXLAS: Characterise bounds for overflow.
234 static __inline unsigned long
235 cubic_cwnd(int usecs_since_epoch, unsigned long wmax, uint32_t smss, int64_t K)
239 /* K is in fixed point form with CUBIC_SHIFT worth of precision. */
241 /* t - K, with CUBIC_SHIFT worth of precision. */
242 cwnd = (((int64_t)usecs_since_epoch << CUBIC_SHIFT) - (K * hz * tick)) /
245 if (cwnd > CUBED_ROOT_MAX_ULONG)
247 if (cwnd < -CUBED_ROOT_MAX_ULONG)
250 /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
251 cwnd *= (cwnd * cwnd);
255 * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
256 * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
257 * and an extra from multiplying through by CUBIC_C_FACTOR.
260 cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax;
263 * for negative cwnd, limiting to zero as lower bound
265 return (lmax(0,cwnd));
269 * Compute an approximation of the NewReno cwnd some number of usecs after a
270 * congestion event. RTT should be the average RTT estimate for the path
271 * measured over the previous congestion epoch and wmax is the value of cwnd at
272 * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
273 * rather tricky to understand and it turns out this function is not required.
274 * It is left here for reference.
278 static __inline unsigned long
279 reno_cwnd(int usecs_since_epoch, int rtt_usecs, unsigned long wmax,
284 * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT
285 * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in
286 * bytes, we have to multiply by smss.
288 return (((wmax * RENO_BETA) + (((usecs_since_epoch * smss)
289 << CUBIC_SHIFT) / rtt_usecs)) >> CUBIC_SHIFT);
293 * Compute an approximation of the "TCP friendly" cwnd some number of usecs
294 * after a congestion event that is designed to yield the same average cwnd as
295 * NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT
296 * estimate for the path measured over the previous congestion epoch and wmax is
297 * the value of cwnd at the last congestion event.
299 static __inline unsigned long
300 tf_cwnd(int usecs_since_epoch, int rtt_usecs, unsigned long wmax,
304 /* Equation 4 of I-D. */
305 return (((wmax * CUBIC_BETA) +
306 (((THREE_X_PT3 * (unsigned long)usecs_since_epoch *
307 (unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_usecs)))
311 #endif /* _NETINET_CC_CUBIC_H_ */