/*- * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org> * Copyright (c) 2010 The FreeBSD Foundation * All rights reserved. * * This software was developed by Lawrence Stewart while studying at the Centre * for Advanced Internet Architectures, Swinburne University of Technology, made * possible in part by a grant from the Cisco University Research Program Fund * at Community Foundation Silicon Valley. * * Portions of this software were developed at the Centre for Advanced * Internet Architectures, Swinburne University of Technology, Melbourne, * Australia by David Hayes under sponsorship from the FreeBSD Foundation. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #ifndef _NETINET_CC_CUBIC_H_ #define _NETINET_CC_CUBIC_H_ #include <sys/limits.h> /* Number of bits of precision for fixed point math calcs. */ #define CUBIC_SHIFT 8 #define CUBIC_SHIFT_4 32 /* 0.5 << CUBIC_SHIFT. */ #define RENO_BETA 128 /* ~0.7 << CUBIC_SHIFT. */ #define CUBIC_BETA 179 /* ~0.3 << CUBIC_SHIFT. */ #define ONE_SUB_CUBIC_BETA 77 /* 3 * ONE_SUB_CUBIC_BETA. */ #define THREE_X_PT3 231 /* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ #define TWO_SUB_PT3 435 /* ~0.4 << CUBIC_SHIFT. */ #define CUBIC_C_FACTOR 102 /* CUBIC fast convergence factor: (1+beta_cubic)/2. */ #define CUBIC_FC_FACTOR 217 /* Don't trust s_rtt until this many rtt samples have been taken. */ #define CUBIC_MIN_RTT_SAMPLES 8 /* * (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor * and taking cube-root yields 448845 as the effective useful limit */ #define CUBED_ROOT_MAX_ULONG 448845 /* Flags used in the cubic structure */ #define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */ #define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */ #define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */ #define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */ #define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */ #define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */ #define CUBICFLAG_IN_TF 0x00000040 /* We are in TCP friendly region */ /* Kernel only bits */ #ifdef _KERNEL struct cubic { /* * CUBIC K in fixed point form with CUBIC_SHIFT worth of precision. * Also means the time period in seconds it takes to increase the * congestion window size at the beginning of the current congestion * avoidance stage to W_max. */ int64_t K; /* Sum of RTT samples across an epoch in usecs. */ int64_t sum_rtt_usecs; /* Size of cwnd (in bytes) just before cwnd was reduced in the last congestion event. */ uint32_t W_max; /* An estimate (in bytes) for the congestion window in the Reno-friendly region */ uint32_t W_est; /* An estimate (in bytes) for the congestion window in the CUBIC region */ uint32_t W_cubic; /* The cwnd (in bytes) at the beginning of the current congestion avoidance stage. */ uint32_t cwnd_epoch; /* various flags */ uint32_t flags; /* Minimum observed rtt in usecs. */ int min_rtt_usecs; /* Mean observed rtt between congestion epochs. */ int mean_rtt_usecs; /* ACKs since last congestion event. */ int epoch_ack_count; /* Timestamp (in ticks) at which the current CA epoch started. */ int t_epoch; /* Timestamp (in ticks) at which the previous CA epoch started. */ int undo_t_epoch; /* Few variables to restore the state after RTO_ERR */ int64_t undo_K; uint32_t undo_W_max; uint32_t undo_cwnd_epoch; uint32_t css_baseline_minrtt; uint32_t css_current_round_minrtt; uint32_t css_lastround_minrtt; uint32_t css_rttsample_count; uint32_t css_entered_at_round; uint32_t css_current_round; uint32_t css_fas_at_css_entry; uint32_t css_lowrtt_fas; uint32_t css_last_fas; }; #endif /* Userland only bits. */ #ifndef _KERNEL extern int hz; /* * Implementation based on the formulas in RFC9438. * */ /* * Returns K, the time period in seconds it takes to increase the congestion * window size at the beginning of the current congestion avoidance stage to * W_max. */ static inline float theoretical_cubic_k(uint32_t wmax_segs, uint32_t cwnd_epoch_segs) { double C; C = 0.4; if (wmax_segs <= cwnd_epoch_segs) return 0.0; /* * Figure 2: K = ((W_max - cwnd_epoch) / C)^(1/3) */ return (pow((wmax_segs - cwnd_epoch_segs) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); } /* * Returns the congestion window in segments at time t in seconds based on the * cubic increase function, where t is the elapsed time in seconds from the * beginning of the current congestion avoidance stage, as described in RFC9438 * Section 4.2. */ static inline unsigned long theoretical_cubic_cwnd(int ticks_elapsed, uint32_t wmax_segs, uint32_t cwnd_epoch_segs) { double C, t; float K; C = 0.4; t = ticks_elapsed / (double)hz; K = theoretical_cubic_k(wmax_segs, cwnd_epoch_segs); /* * Figure 1: W_cubic(t) = C * (t - K)^3 + W_max */ return (C * pow(t - K / pow(2, CUBIC_SHIFT), 3.0) + wmax_segs); } /* * Returns estimated Reno congestion window in segments. */ static inline unsigned long theoretical_reno_cwnd(int ticks_elapsed, int rtt_ticks, uint32_t wmax_segs) { return (wmax_segs * 0.5 + ticks_elapsed / (float)rtt_ticks); } /* * Returns an estimate for the congestion window in segments in the * Reno-friendly region -- that is, an estimate for the congestion window of * Reno, as described in RFC9438 Section 4.3, where: * cwnd: Current congestion window in segments. * cwnd_prior: Size of cwnd in segments at the time of setting ssthresh most * recently, either upon exiting the first slow start or just before * cwnd was reduced in the last congestion event. * W_est: An estimate for the congestion window in segments in the Reno-friendly * region -- that is, an estimate for the congestion window of Reno. */ static inline unsigned long theoretical_tf_cwnd(unsigned long W_est, unsigned long segs_acked, unsigned long cwnd, unsigned long cwnd_prior) { float cubic_alpha, cubic_beta; /* RFC9438 Section 4.6: The parameter β_cubic SHOULD be set to 0.7. */ cubic_beta = 0.7; if (W_est >= cwnd_prior) cubic_alpha = 1.0; else cubic_alpha = (3.0 * (1.0 - cubic_beta)) / (1.0 + cubic_beta); /* * Figure 4: W_est = W_est + α_cubic * segments_acked / cwnd */ return (W_est + cubic_alpha * segs_acked / cwnd); } #endif /* !_KERNEL */ /* * Compute the CUBIC K value used in the cwnd calculation, using an * implementation mentioned in Figure. 2 of RFC9438. * The method used here is adapted from Apple Computer Technical Report #KT-32. */ static inline int64_t cubic_k(uint32_t wmax_segs, uint32_t cwnd_epoch_segs) { int64_t s, K; uint16_t p; K = s = 0; p = 0; /* Handle the corner case where W_max <= cwnd_epoch */ if (wmax_segs <= cwnd_epoch_segs) { return 0; } /* (wmax - cwnd_epoch) / C with CUBIC_SHIFT worth of precision. */ s = ((wmax_segs - cwnd_epoch_segs) << (2 * CUBIC_SHIFT)) / CUBIC_C_FACTOR; /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ while (s >= 256) { s >>= 3; p++; } /* * Some magic constants taken from the Apple TR with appropriate * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. */ K = (((s * 275) >> CUBIC_SHIFT) + 98) - (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); /* Multiply by 2^p to undo the rebasing of s from above. */ return (K <<= p); } /* * Compute and return the new cwnd value in bytes using an implementation * mentioned in Figure. 1 of RFC9438. * Thanks to Kip Macy for help debugging this function. * * XXXLAS: Characterise bounds for overflow. */ static inline uint32_t cubic_cwnd(int usecs_since_epoch, uint32_t wmax, uint32_t smss, int64_t K) { int64_t cwnd; /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ /* t - K, with CUBIC_SHIFT worth of precision. */ cwnd = (((int64_t)usecs_since_epoch << CUBIC_SHIFT) - (K * hz * tick)) / (hz * tick); if (cwnd > CUBED_ROOT_MAX_ULONG) return INT_MAX; if (cwnd < -CUBED_ROOT_MAX_ULONG) return 0; /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ cwnd *= (cwnd * cwnd); /* * Figure 1: C * (t - K)^3 + wmax * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, * and an extra from multiplying through by CUBIC_C_FACTOR. */ cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax; /* * for negative cwnd, limiting to zero as lower bound */ return (lmax(0,cwnd)); } /* * Compute the "TCP friendly" cwnd by newreno in congestion avoidance state. */ static inline uint32_t tf_cwnd(struct cc_var *ccv) { /* newreno is "TCP friendly" */ return newreno_cc_cwnd_in_cong_avoid(ccv); } #endif /* _NETINET_CC_CUBIC_H_ */
