cc_htcp.c revision 220560
1216115Slstewart/*- 2216115Slstewart * Copyright (c) 2007-2008 3216115Slstewart * Swinburne University of Technology, Melbourne, Australia 4216115Slstewart * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org> 5216115Slstewart * Copyright (c) 2010 The FreeBSD Foundation 6216115Slstewart * All rights reserved. 7216115Slstewart * 8216115Slstewart * This software was developed at the Centre for Advanced Internet 9220560Slstewart * Architectures, Swinburne University of Technology, by Lawrence Stewart and 10220560Slstewart * James Healy, made possible in part by a grant from the Cisco University 11220560Slstewart * Research Program Fund at Community Foundation Silicon Valley. 12216115Slstewart * 13216115Slstewart * Portions of this software were developed at the Centre for Advanced 14216115Slstewart * Internet Architectures, Swinburne University of Technology, Melbourne, 15216115Slstewart * Australia by David Hayes under sponsorship from the FreeBSD Foundation. 16216115Slstewart * 17216115Slstewart * Redistribution and use in source and binary forms, with or without 18216115Slstewart * modification, are permitted provided that the following conditions 19216115Slstewart * are met: 20216115Slstewart * 1. Redistributions of source code must retain the above copyright 21216115Slstewart * notice, this list of conditions and the following disclaimer. 22216115Slstewart * 2. Redistributions in binary form must reproduce the above copyright 23216115Slstewart * notice, this list of conditions and the following disclaimer in the 24216115Slstewart * documentation and/or other materials provided with the distribution. 25216115Slstewart * 26216115Slstewart * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 27216115Slstewart * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28216115Slstewart * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29216115Slstewart * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 30216115Slstewart * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31216115Slstewart * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32216115Slstewart * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33216115Slstewart * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34216115Slstewart * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35216115Slstewart * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36216115Slstewart * SUCH DAMAGE. 37216115Slstewart */ 38216115Slstewart 39216115Slstewart/* 40216115Slstewart * An implementation of the H-TCP congestion control algorithm for FreeBSD, 41216115Slstewart * based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and 42216115Slstewart * Shorten. Originally released as part of the NewTCP research project at 43220560Slstewart * Swinburne University of Technology's Centre for Advanced Internet 44220560Slstewart * Architectures, Melbourne, Australia, which was made possible in part by a 45220560Slstewart * grant from the Cisco University Research Program Fund at Community Foundation 46220560Slstewart * Silicon Valley. More details are available at: 47216115Slstewart * http://caia.swin.edu.au/urp/newtcp/ 48216115Slstewart */ 49216115Slstewart 50216115Slstewart#include <sys/cdefs.h> 51216115Slstewart__FBSDID("$FreeBSD: head/sys/netinet/cc/cc_htcp.c 220560 2011-04-12 08:13:18Z lstewart $"); 52216115Slstewart 53216115Slstewart#include <sys/param.h> 54216115Slstewart#include <sys/kernel.h> 55216115Slstewart#include <sys/limits.h> 56216115Slstewart#include <sys/malloc.h> 57216115Slstewart#include <sys/module.h> 58216115Slstewart#include <sys/socket.h> 59216115Slstewart#include <sys/socketvar.h> 60216115Slstewart#include <sys/sysctl.h> 61216115Slstewart#include <sys/systm.h> 62216115Slstewart 63216115Slstewart#include <net/vnet.h> 64216115Slstewart 65216115Slstewart#include <netinet/cc.h> 66216115Slstewart#include <netinet/tcp_seq.h> 67216115Slstewart#include <netinet/tcp_timer.h> 68216115Slstewart#include <netinet/tcp_var.h> 69216115Slstewart 70216115Slstewart#include <netinet/cc/cc_module.h> 71216115Slstewart 72216115Slstewart/* Fixed point math shifts. */ 73216115Slstewart#define HTCP_SHIFT 8 74216115Slstewart#define HTCP_ALPHA_INC_SHIFT 4 75216115Slstewart 76216115Slstewart#define HTCP_INIT_ALPHA 1 77216115Slstewart#define HTCP_DELTA_L hz /* 1 sec in ticks. */ 78216115Slstewart#define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */ 79216115Slstewart#define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */ 80216115Slstewart#define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */ 81216115Slstewart#define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */ 82216115Slstewart 83216115Slstewart/* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */ 84216115Slstewart#define HTCP_RTT_REF 100 85216115Slstewart 86216115Slstewart/* Don't trust SRTT until this many samples have been taken. */ 87216115Slstewart#define HTCP_MIN_RTT_SAMPLES 8 88216115Slstewart 89216115Slstewart/* 90216115Slstewart * HTCP_CALC_ALPHA performs a fixed point math calculation to determine the 91216115Slstewart * value of alpha, based on the function defined in the HTCP spec. 92216115Slstewart * 93216115Slstewart * i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2 94216115Slstewart * 95216115Slstewart * "diff" is passed in to the macro as "delta - delta_l" and is expected to be 96216115Slstewart * in units of ticks. 97216115Slstewart * 98216115Slstewart * The joyousnous of fixed point maths means our function implementation looks a 99216115Slstewart * little funky... 100216115Slstewart * 101216115Slstewart * In order to maintain some precision in the calculations, a fixed point shift 102216115Slstewart * HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't 103216115Slstewart * truncate the results too badly. 104216115Slstewart * 105216115Slstewart * The "16" value is the "1" term in the alpha function shifted up by 106216115Slstewart * HTCP_ALPHA_INC_SHIFT 107216115Slstewart * 108216115Slstewart * The "160" value is the "10" multiplier in the alpha function multiplied by 109216115Slstewart * 2^HTCP_ALPHA_INC_SHIFT 110216115Slstewart * 111216115Slstewart * Specifying these as constants reduces the computations required. After 112216115Slstewart * up-shifting all the terms in the function and performing the required 113216115Slstewart * calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to 114216115Slstewart * ensure it is back in the correct range. 115216115Slstewart * 116216115Slstewart * The "hz" terms are required as kernels can be configured to run with 117216115Slstewart * different tick timers, which we have to adjust for in the alpha calculation 118216115Slstewart * (which originally was defined in terms of seconds). 119216115Slstewart * 120216115Slstewart * We also have to be careful to constrain the value of diff such that it won't 121216115Slstewart * overflow whilst performing the calculation. The middle term i.e. (160 * diff) 122216115Slstewart * / hz is the limiting factor in the calculation. We must constrain diff to be 123216115Slstewart * less than the max size of an int divided by the constant 160 figure 124216115Slstewart * i.e. diff < INT_MAX / 160 125216115Slstewart * 126216115Slstewart * NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the 127216115Slstewart * constants used in this function! 128216115Slstewart */ 129216115Slstewart#define HTCP_CALC_ALPHA(diff) \ 130216115Slstewart((\ 131216115Slstewart (16) + \ 132216115Slstewart ((160 * (diff)) / hz) + \ 133216115Slstewart (((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \ 134216115Slstewart) >> HTCP_ALPHA_INC_SHIFT) 135216115Slstewart 136216115Slstewartstatic void htcp_ack_received(struct cc_var *ccv, uint16_t type); 137216115Slstewartstatic void htcp_cb_destroy(struct cc_var *ccv); 138216115Slstewartstatic int htcp_cb_init(struct cc_var *ccv); 139216115Slstewartstatic void htcp_cong_signal(struct cc_var *ccv, uint32_t type); 140216115Slstewartstatic int htcp_mod_init(void); 141216115Slstewartstatic void htcp_post_recovery(struct cc_var *ccv); 142216115Slstewartstatic void htcp_recalc_alpha(struct cc_var *ccv); 143216115Slstewartstatic void htcp_recalc_beta(struct cc_var *ccv); 144216115Slstewartstatic void htcp_record_rtt(struct cc_var *ccv); 145216115Slstewartstatic void htcp_ssthresh_update(struct cc_var *ccv); 146216115Slstewart 147216115Slstewartstruct htcp { 148216115Slstewart /* cwnd before entering cong recovery. */ 149216115Slstewart unsigned long prev_cwnd; 150216115Slstewart /* cwnd additive increase parameter. */ 151216115Slstewart int alpha; 152216115Slstewart /* cwnd multiplicative decrease parameter. */ 153216115Slstewart int beta; 154216115Slstewart /* Largest rtt seen for the flow. */ 155216115Slstewart int maxrtt; 156216115Slstewart /* Shortest rtt seen for the flow. */ 157216115Slstewart int minrtt; 158216115Slstewart /* Time of last congestion event in ticks. */ 159216115Slstewart int t_last_cong; 160216115Slstewart}; 161216115Slstewart 162216115Slstewartstatic int htcp_rtt_ref; 163216115Slstewart/* 164216115Slstewart * The maximum number of ticks the value of diff can reach in 165216115Slstewart * htcp_recalc_alpha() before alpha will stop increasing due to overflow. 166216115Slstewart * See comment above HTCP_CALC_ALPHA for more info. 167216115Slstewart */ 168216115Slstewartstatic int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10); 169216115Slstewart 170216115Slstewart/* Per-netstack vars. */ 171217322Smdfstatic VNET_DEFINE(u_int, htcp_adaptive_backoff) = 0; 172217322Smdfstatic VNET_DEFINE(u_int, htcp_rtt_scaling) = 0; 173216115Slstewart#define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff) 174216115Slstewart#define V_htcp_rtt_scaling VNET(htcp_rtt_scaling) 175216115Slstewart 176216115SlstewartMALLOC_DECLARE(M_HTCP); 177216115SlstewartMALLOC_DEFINE(M_HTCP, "htcp data", 178216115Slstewart "Per connection data required for the HTCP congestion control algorithm"); 179216115Slstewart 180216115Slstewartstruct cc_algo htcp_cc_algo = { 181216115Slstewart .name = "htcp", 182216115Slstewart .ack_received = htcp_ack_received, 183216115Slstewart .cb_destroy = htcp_cb_destroy, 184216115Slstewart .cb_init = htcp_cb_init, 185216115Slstewart .cong_signal = htcp_cong_signal, 186216115Slstewart .mod_init = htcp_mod_init, 187216115Slstewart .post_recovery = htcp_post_recovery, 188216115Slstewart}; 189216115Slstewart 190216115Slstewartstatic void 191216115Slstewarthtcp_ack_received(struct cc_var *ccv, uint16_t type) 192216115Slstewart{ 193216115Slstewart struct htcp *htcp_data; 194216115Slstewart 195216115Slstewart htcp_data = ccv->cc_data; 196216115Slstewart htcp_record_rtt(ccv); 197216115Slstewart 198216115Slstewart /* 199216115Slstewart * Regular ACK and we're not in cong/fast recovery and we're cwnd 200216115Slstewart * limited and we're either not doing ABC or are slow starting or are 201216115Slstewart * doing ABC and we've sent a cwnd's worth of bytes. 202216115Slstewart */ 203216115Slstewart if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 204216115Slstewart (ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 || 205216115Slstewart CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) || 206216115Slstewart (V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) { 207216115Slstewart htcp_recalc_beta(ccv); 208216115Slstewart htcp_recalc_alpha(ccv); 209216115Slstewart /* 210216115Slstewart * Use the logic in NewReno ack_received() for slow start and 211216115Slstewart * for the first HTCP_DELTA_L ticks after either the flow starts 212216115Slstewart * or a congestion event (when alpha equals 1). 213216115Slstewart */ 214216115Slstewart if (htcp_data->alpha == 1 || 215216115Slstewart CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) 216216115Slstewart newreno_cc_algo.ack_received(ccv, type); 217216115Slstewart else { 218216115Slstewart if (V_tcp_do_rfc3465) { 219216115Slstewart /* Increment cwnd by alpha segments. */ 220216115Slstewart CCV(ccv, snd_cwnd) += htcp_data->alpha * 221216115Slstewart CCV(ccv, t_maxseg); 222216115Slstewart ccv->flags &= ~CCF_ABC_SENTAWND; 223216115Slstewart } else 224216115Slstewart /* 225216115Slstewart * Increment cwnd by alpha/cwnd segments to 226216115Slstewart * approximate an increase of alpha segments 227216115Slstewart * per RTT. 228216115Slstewart */ 229216115Slstewart CCV(ccv, snd_cwnd) += (((htcp_data->alpha << 230216115Slstewart HTCP_SHIFT) / (CCV(ccv, snd_cwnd) / 231216115Slstewart CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg)) 232216115Slstewart >> HTCP_SHIFT; 233216115Slstewart } 234216115Slstewart } 235216115Slstewart} 236216115Slstewart 237216115Slstewartstatic void 238216115Slstewarthtcp_cb_destroy(struct cc_var *ccv) 239216115Slstewart{ 240216115Slstewart 241216115Slstewart if (ccv->cc_data != NULL) 242216115Slstewart free(ccv->cc_data, M_HTCP); 243216115Slstewart} 244216115Slstewart 245216115Slstewartstatic int 246216115Slstewarthtcp_cb_init(struct cc_var *ccv) 247216115Slstewart{ 248216115Slstewart struct htcp *htcp_data; 249216115Slstewart 250216115Slstewart htcp_data = malloc(sizeof(struct htcp), M_HTCP, M_NOWAIT); 251216115Slstewart 252216115Slstewart if (htcp_data == NULL) 253216115Slstewart return (ENOMEM); 254216115Slstewart 255216115Slstewart /* Init some key variables with sensible defaults. */ 256216115Slstewart htcp_data->alpha = HTCP_INIT_ALPHA; 257216115Slstewart htcp_data->beta = HTCP_MINBETA; 258216115Slstewart htcp_data->maxrtt = TCPTV_SRTTBASE; 259216115Slstewart htcp_data->minrtt = TCPTV_SRTTBASE; 260216115Slstewart htcp_data->prev_cwnd = 0; 261216115Slstewart htcp_data->t_last_cong = ticks; 262216115Slstewart 263216115Slstewart ccv->cc_data = htcp_data; 264216115Slstewart 265216115Slstewart return (0); 266216115Slstewart} 267216115Slstewart 268216115Slstewart/* 269216115Slstewart * Perform any necessary tasks before we enter congestion recovery. 270216115Slstewart */ 271216115Slstewartstatic void 272216115Slstewarthtcp_cong_signal(struct cc_var *ccv, uint32_t type) 273216115Slstewart{ 274216115Slstewart struct htcp *htcp_data; 275216115Slstewart 276216115Slstewart htcp_data = ccv->cc_data; 277216115Slstewart 278216115Slstewart switch (type) { 279216115Slstewart case CC_NDUPACK: 280216115Slstewart if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 281216115Slstewart if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 282216115Slstewart /* 283216115Slstewart * Apply hysteresis to maxrtt to ensure 284216115Slstewart * reductions in the RTT are reflected in our 285216115Slstewart * measurements. 286216115Slstewart */ 287216115Slstewart htcp_data->maxrtt = (htcp_data->minrtt + 288216115Slstewart (htcp_data->maxrtt - htcp_data->minrtt) * 289216115Slstewart 95) / 100; 290216115Slstewart htcp_ssthresh_update(ccv); 291216115Slstewart htcp_data->t_last_cong = ticks; 292216115Slstewart htcp_data->prev_cwnd = CCV(ccv, snd_cwnd); 293216115Slstewart } 294216115Slstewart ENTER_RECOVERY(CCV(ccv, t_flags)); 295216115Slstewart } 296216115Slstewart break; 297216115Slstewart 298216115Slstewart case CC_ECN: 299216115Slstewart if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 300216115Slstewart /* 301216115Slstewart * Apply hysteresis to maxrtt to ensure reductions in 302216115Slstewart * the RTT are reflected in our measurements. 303216115Slstewart */ 304216115Slstewart htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt - 305216115Slstewart htcp_data->minrtt) * 95) / 100; 306216115Slstewart htcp_ssthresh_update(ccv); 307216115Slstewart CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 308216115Slstewart htcp_data->t_last_cong = ticks; 309216115Slstewart htcp_data->prev_cwnd = CCV(ccv, snd_cwnd); 310216115Slstewart ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 311216115Slstewart } 312216115Slstewart break; 313216115Slstewart 314216115Slstewart case CC_RTO: 315216115Slstewart /* 316216115Slstewart * Grab the current time and record it so we know when the 317216115Slstewart * most recent congestion event was. Only record it when the 318216115Slstewart * timeout has fired more than once, as there is a reasonable 319216115Slstewart * chance the first one is a false alarm and may not indicate 320216115Slstewart * congestion. 321216115Slstewart */ 322216115Slstewart if (CCV(ccv, t_rxtshift) >= 2) 323216115Slstewart htcp_data->t_last_cong = ticks; 324216115Slstewart break; 325216115Slstewart } 326216115Slstewart} 327216115Slstewart 328216115Slstewartstatic int 329216115Slstewarthtcp_mod_init(void) 330216115Slstewart{ 331216115Slstewart 332216115Slstewart htcp_cc_algo.after_idle = newreno_cc_algo.after_idle; 333216115Slstewart 334216115Slstewart /* 335216115Slstewart * HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in 336216115Slstewart * units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units 337216115Slstewart * as t_srtt. 338216115Slstewart */ 339216115Slstewart htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000; 340216115Slstewart 341216115Slstewart return (0); 342216115Slstewart} 343216115Slstewart 344216115Slstewart/* 345216115Slstewart * Perform any necessary tasks before we exit congestion recovery. 346216115Slstewart */ 347216115Slstewartstatic void 348216115Slstewarthtcp_post_recovery(struct cc_var *ccv) 349216115Slstewart{ 350216115Slstewart struct htcp *htcp_data; 351216115Slstewart 352216115Slstewart htcp_data = ccv->cc_data; 353216115Slstewart 354216115Slstewart if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { 355216115Slstewart /* 356216115Slstewart * If inflight data is less than ssthresh, set cwnd 357216115Slstewart * conservatively to avoid a burst of data, as suggested in the 358216115Slstewart * NewReno RFC. Otherwise, use the HTCP method. 359216115Slstewart * 360216115Slstewart * XXXLAS: Find a way to do this without needing curack 361216115Slstewart */ 362216115Slstewart if (SEQ_GT(ccv->curack + CCV(ccv, snd_ssthresh), 363216115Slstewart CCV(ccv, snd_max))) 364216115Slstewart CCV(ccv, snd_cwnd) = CCV(ccv, snd_max) - ccv->curack + 365216115Slstewart CCV(ccv, t_maxseg); 366216115Slstewart else 367216115Slstewart CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta * 368216115Slstewart htcp_data->prev_cwnd / CCV(ccv, t_maxseg)) 369216115Slstewart >> HTCP_SHIFT)) * CCV(ccv, t_maxseg); 370216115Slstewart } 371216115Slstewart} 372216115Slstewart 373216115Slstewartstatic void 374216115Slstewarthtcp_recalc_alpha(struct cc_var *ccv) 375216115Slstewart{ 376216115Slstewart struct htcp *htcp_data; 377216115Slstewart int alpha, diff, now; 378216115Slstewart 379216115Slstewart htcp_data = ccv->cc_data; 380216115Slstewart now = ticks; 381216115Slstewart 382216115Slstewart /* 383216115Slstewart * If ticks has wrapped around (will happen approximately once every 49 384216115Slstewart * days on a machine with the default kern.hz=1000) and a flow straddles 385216115Slstewart * the wrap point, our alpha calcs will be completely wrong. We cut our 386216115Slstewart * losses and restart alpha from scratch by setting t_last_cong = now - 387216115Slstewart * HTCP_DELTA_L. 388216115Slstewart * 389216115Slstewart * This does not deflate our cwnd at all. It simply slows the rate cwnd 390216115Slstewart * is growing by until alpha regains the value it held prior to taking 391216115Slstewart * this drastic measure. 392216115Slstewart */ 393216115Slstewart if (now < htcp_data->t_last_cong) 394216115Slstewart htcp_data->t_last_cong = now - HTCP_DELTA_L; 395216115Slstewart 396216115Slstewart diff = now - htcp_data->t_last_cong - HTCP_DELTA_L; 397216115Slstewart 398216115Slstewart /* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */ 399216115Slstewart if (diff < htcp_max_diff) { 400216115Slstewart /* 401216115Slstewart * If it has been more than HTCP_DELTA_L ticks since congestion, 402216115Slstewart * increase alpha according to the function defined in the spec. 403216115Slstewart */ 404216115Slstewart if (diff > 0) { 405216115Slstewart alpha = HTCP_CALC_ALPHA(diff); 406216115Slstewart 407216115Slstewart /* 408216115Slstewart * Adaptive backoff fairness adjustment: 409216115Slstewart * 2 * (1 - beta) * alpha_raw 410216115Slstewart */ 411216115Slstewart if (V_htcp_adaptive_backoff) 412216115Slstewart alpha = max(1, (2 * ((1 << HTCP_SHIFT) - 413216115Slstewart htcp_data->beta) * alpha) >> HTCP_SHIFT); 414216115Slstewart 415216115Slstewart /* 416216115Slstewart * RTT scaling: (RTT / RTT_ref) * alpha 417216115Slstewart * alpha will be the raw value from HTCP_CALC_ALPHA() if 418216115Slstewart * adaptive backoff is off, or the adjusted value if 419216115Slstewart * adaptive backoff is on. 420216115Slstewart */ 421216115Slstewart if (V_htcp_rtt_scaling) 422216115Slstewart alpha = max(1, (min(max(HTCP_MINROWE, 423216115Slstewart (CCV(ccv, t_srtt) << HTCP_SHIFT) / 424216115Slstewart htcp_rtt_ref), HTCP_MAXROWE) * alpha) 425216115Slstewart >> HTCP_SHIFT); 426216115Slstewart 427216115Slstewart } else 428216115Slstewart alpha = 1; 429216115Slstewart 430216115Slstewart htcp_data->alpha = alpha; 431216115Slstewart } 432216115Slstewart} 433216115Slstewart 434216115Slstewartstatic void 435216115Slstewarthtcp_recalc_beta(struct cc_var *ccv) 436216115Slstewart{ 437216115Slstewart struct htcp *htcp_data; 438216115Slstewart 439216115Slstewart htcp_data = ccv->cc_data; 440216115Slstewart 441216115Slstewart /* 442216115Slstewart * TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so 443216115Slstewart * we only calc beta if the connection's SRTT has been changed from its 444216115Slstewart * inital value. beta is bounded to ensure it is always between 445216115Slstewart * HTCP_MINBETA and HTCP_MAXBETA. 446216115Slstewart */ 447216115Slstewart if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE && 448216115Slstewart htcp_data->maxrtt != TCPTV_SRTTBASE) 449216115Slstewart htcp_data->beta = min(max(HTCP_MINBETA, 450216115Slstewart (htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt), 451216115Slstewart HTCP_MAXBETA); 452216115Slstewart else 453216115Slstewart htcp_data->beta = HTCP_MINBETA; 454216115Slstewart} 455216115Slstewart 456216115Slstewart/* 457216115Slstewart * Record the minimum and maximum RTT seen for the connection. These are used in 458216115Slstewart * the calculation of beta if adaptive backoff is enabled. 459216115Slstewart */ 460216115Slstewartstatic void 461216115Slstewarthtcp_record_rtt(struct cc_var *ccv) 462216115Slstewart{ 463216115Slstewart struct htcp *htcp_data; 464216115Slstewart 465216115Slstewart htcp_data = ccv->cc_data; 466216115Slstewart 467216115Slstewart /* XXXLAS: Should there be some hysteresis for minrtt? */ 468216115Slstewart 469216115Slstewart /* 470216115Slstewart * Record the current SRTT as our minrtt if it's the smallest we've seen 471216115Slstewart * or minrtt is currently equal to its initialised value. Ignore SRTT 472216115Slstewart * until a min number of samples have been taken. 473216115Slstewart */ 474216115Slstewart if ((CCV(ccv, t_srtt) < htcp_data->minrtt || 475216115Slstewart htcp_data->minrtt == TCPTV_SRTTBASE) && 476216115Slstewart (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)) 477216115Slstewart htcp_data->minrtt = CCV(ccv, t_srtt); 478216115Slstewart 479216115Slstewart /* 480216115Slstewart * Record the current SRTT as our maxrtt if it's the largest we've 481216115Slstewart * seen. Ignore SRTT until a min number of samples have been taken. 482216115Slstewart */ 483216115Slstewart if (CCV(ccv, t_srtt) > htcp_data->maxrtt 484216115Slstewart && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES) 485216115Slstewart htcp_data->maxrtt = CCV(ccv, t_srtt); 486216115Slstewart} 487216115Slstewart 488216115Slstewart/* 489216115Slstewart * Update the ssthresh in the event of congestion. 490216115Slstewart */ 491216115Slstewartstatic void 492216115Slstewarthtcp_ssthresh_update(struct cc_var *ccv) 493216115Slstewart{ 494216115Slstewart struct htcp *htcp_data; 495216115Slstewart 496216115Slstewart htcp_data = ccv->cc_data; 497216115Slstewart 498216115Slstewart /* 499216115Slstewart * On the first congestion event, set ssthresh to cwnd * 0.5, on 500216115Slstewart * subsequent congestion events, set it to cwnd * beta. 501216115Slstewart */ 502216115Slstewart if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT) 503216115Slstewart CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * HTCP_MINBETA) 504216115Slstewart >> HTCP_SHIFT; 505216115Slstewart else { 506216115Slstewart htcp_recalc_beta(ccv); 507216115Slstewart CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * htcp_data->beta) 508216115Slstewart >> HTCP_SHIFT; 509216115Slstewart } 510216115Slstewart} 511216115Slstewart 512216115Slstewart 513216115SlstewartSYSCTL_DECL(_net_inet_tcp_cc_htcp); 514216115SlstewartSYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW, 515216115Slstewart NULL, "H-TCP related settings"); 516216115SlstewartSYSCTL_VNET_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff, CTLFLAG_RW, 517216115Slstewart &VNET_NAME(htcp_adaptive_backoff), 0, "enable H-TCP adaptive backoff"); 518216115SlstewartSYSCTL_VNET_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling, CTLFLAG_RW, 519216115Slstewart &VNET_NAME(htcp_rtt_scaling), 0, "enable H-TCP RTT scaling"); 520216115Slstewart 521216115SlstewartDECLARE_CC_MODULE(htcp, &htcp_cc_algo); 522