cc_htcp.c revision 299280
1169689Skan/*- 2169689Skan * Copyright (c) 2007-2008 3169689Skan * Swinburne University of Technology, Melbourne, Australia 4169689Skan * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org> 5169689Skan * Copyright (c) 2010 The FreeBSD Foundation 6169689Skan * All rights reserved. 7169689Skan * 8169689Skan * This software was developed at the Centre for Advanced Internet 9169689Skan * Architectures, Swinburne University of Technology, by Lawrence Stewart and 10169689Skan * James Healy, made possible in part by a grant from the Cisco University 11169689Skan * Research Program Fund at Community Foundation Silicon Valley. 12169689Skan * 13169689Skan * Portions of this software were developed at the Centre for Advanced 14169689Skan * Internet Architectures, Swinburne University of Technology, Melbourne, 15169689Skan * Australia by David Hayes under sponsorship from the FreeBSD Foundation. 16169689Skan * 17169689Skan * Redistribution and use in source and binary forms, with or without 18169689Skan * modification, are permitted provided that the following conditions 19169689Skan * are met: 20169689Skan * 1. Redistributions of source code must retain the above copyright 21169689Skan * notice, this list of conditions and the following disclaimer. 22169689Skan * 2. Redistributions in binary form must reproduce the above copyright 23169689Skan * notice, this list of conditions and the following disclaimer in the 24169689Skan * documentation and/or other materials provided with the distribution. 25169689Skan * 26169689Skan * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 27169689Skan * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28169689Skan * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29169689Skan * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 30169689Skan * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31169689Skan * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32169689Skan * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33169689Skan * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34169689Skan * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35169689Skan * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36169689Skan * SUCH DAMAGE. 37169689Skan */ 38169689Skan 39169689Skan/* 40169689Skan * An implementation of the H-TCP congestion control algorithm for FreeBSD, 41169689Skan * based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and 42169689Skan * Shorten. Originally released as part of the NewTCP research project at 43169689Skan * Swinburne University of Technology's Centre for Advanced Internet 44169689Skan * Architectures, Melbourne, Australia, which was made possible in part by a 45169689Skan * grant from the Cisco University Research Program Fund at Community Foundation 46169689Skan * Silicon Valley. More details are available at: 47169689Skan * http://caia.swin.edu.au/urp/newtcp/ 48169689Skan */ 49169689Skan 50169689Skan#include <sys/cdefs.h> 51169689Skan__FBSDID("$FreeBSD: head/sys/netinet/cc/cc_htcp.c 299280 2016-05-09 19:19:03Z hiren $"); 52169689Skan 53169689Skan#include <sys/param.h> 54169689Skan#include <sys/kernel.h> 55169689Skan#include <sys/limits.h> 56169689Skan#include <sys/malloc.h> 57169689Skan#include <sys/module.h> 58169689Skan#include <sys/socket.h> 59169689Skan#include <sys/socketvar.h> 60169689Skan#include <sys/sysctl.h> 61169689Skan#include <sys/systm.h> 62169689Skan 63169689Skan#include <net/vnet.h> 64169689Skan 65169689Skan#include <netinet/tcp.h> 66169689Skan#include <netinet/tcp_seq.h> 67169689Skan#include <netinet/tcp_timer.h> 68169689Skan#include <netinet/tcp_var.h> 69169689Skan#include <netinet/cc/cc.h> 70169689Skan#include <netinet/cc/cc_module.h> 71169689Skan 72169689Skan/* Fixed point math shifts. */ 73169689Skan#define HTCP_SHIFT 8 74169689Skan#define HTCP_ALPHA_INC_SHIFT 4 75169689Skan 76169689Skan#define HTCP_INIT_ALPHA 1 77169689Skan#define HTCP_DELTA_L hz /* 1 sec in ticks. */ 78169689Skan#define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */ 79169689Skan#define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */ 80169689Skan#define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */ 81169689Skan#define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */ 82169689Skan 83169689Skan/* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */ 84169689Skan#define HTCP_RTT_REF 100 85169689Skan 86169689Skan/* Don't trust SRTT until this many samples have been taken. */ 87169689Skan#define HTCP_MIN_RTT_SAMPLES 8 88169689Skan 89169689Skan/* 90169689Skan * HTCP_CALC_ALPHA performs a fixed point math calculation to determine the 91169689Skan * value of alpha, based on the function defined in the HTCP spec. 92169689Skan * 93169689Skan * i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2 94169689Skan * 95169689Skan * "diff" is passed in to the macro as "delta - delta_l" and is expected to be 96169689Skan * in units of ticks. 97169689Skan * 98169689Skan * The joyousnous of fixed point maths means our function implementation looks a 99169689Skan * little funky... 100169689Skan * 101169689Skan * In order to maintain some precision in the calculations, a fixed point shift 102169689Skan * HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't 103169689Skan * truncate the results too badly. 104169689Skan * 105169689Skan * The "16" value is the "1" term in the alpha function shifted up by 106169689Skan * HTCP_ALPHA_INC_SHIFT 107169689Skan * 108169689Skan * The "160" value is the "10" multiplier in the alpha function multiplied by 109169689Skan * 2^HTCP_ALPHA_INC_SHIFT 110169689Skan * 111169689Skan * Specifying these as constants reduces the computations required. After 112169689Skan * up-shifting all the terms in the function and performing the required 113169689Skan * calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to 114169689Skan * ensure it is back in the correct range. 115169689Skan * 116169689Skan * The "hz" terms are required as kernels can be configured to run with 117169689Skan * different tick timers, which we have to adjust for in the alpha calculation 118169689Skan * (which originally was defined in terms of seconds). 119169689Skan * 120169689Skan * We also have to be careful to constrain the value of diff such that it won't 121169689Skan * overflow whilst performing the calculation. The middle term i.e. (160 * diff) 122169689Skan * / hz is the limiting factor in the calculation. We must constrain diff to be 123169689Skan * less than the max size of an int divided by the constant 160 figure 124169689Skan * i.e. diff < INT_MAX / 160 125169689Skan * 126169689Skan * NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the 127169689Skan * constants used in this function! 128169689Skan */ 129169689Skan#define HTCP_CALC_ALPHA(diff) \ 130169689Skan((\ 131169689Skan (16) + \ 132169689Skan ((160 * (diff)) / hz) + \ 133169689Skan (((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \ 134169689Skan) >> HTCP_ALPHA_INC_SHIFT) 135169689Skan 136169689Skanstatic void htcp_ack_received(struct cc_var *ccv, uint16_t type); 137169689Skanstatic void htcp_cb_destroy(struct cc_var *ccv); 138169689Skanstatic int htcp_cb_init(struct cc_var *ccv); 139169689Skanstatic void htcp_cong_signal(struct cc_var *ccv, uint32_t type); 140169689Skanstatic int htcp_mod_init(void); 141169689Skanstatic void htcp_post_recovery(struct cc_var *ccv); 142169689Skanstatic void htcp_recalc_alpha(struct cc_var *ccv); 143169689Skanstatic void htcp_recalc_beta(struct cc_var *ccv); 144169689Skanstatic void htcp_record_rtt(struct cc_var *ccv); 145169689Skanstatic void htcp_ssthresh_update(struct cc_var *ccv); 146169689Skan 147169689Skanstruct htcp { 148169689Skan /* cwnd before entering cong recovery. */ 149169689Skan unsigned long prev_cwnd; 150169689Skan /* cwnd additive increase parameter. */ 151169689Skan int alpha; 152169689Skan /* cwnd multiplicative decrease parameter. */ 153169689Skan int beta; 154169689Skan /* Largest rtt seen for the flow. */ 155169689Skan int maxrtt; 156169689Skan /* Shortest rtt seen for the flow. */ 157169689Skan int minrtt; 158169689Skan /* Time of last congestion event in ticks. */ 159169689Skan int t_last_cong; 160169689Skan}; 161169689Skan 162169689Skanstatic int htcp_rtt_ref; 163169689Skan/* 164169689Skan * The maximum number of ticks the value of diff can reach in 165169689Skan * htcp_recalc_alpha() before alpha will stop increasing due to overflow. 166169689Skan * See comment above HTCP_CALC_ALPHA for more info. 167169689Skan */ 168169689Skanstatic int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10); 169169689Skan 170169689Skan/* Per-netstack vars. */ 171169689Skanstatic VNET_DEFINE(u_int, htcp_adaptive_backoff) = 0; 172169689Skanstatic VNET_DEFINE(u_int, htcp_rtt_scaling) = 0; 173169689Skan#define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff) 174169689Skan#define V_htcp_rtt_scaling VNET(htcp_rtt_scaling) 175169689Skan 176169689Skanstatic MALLOC_DEFINE(M_HTCP, "htcp data", 177169689Skan "Per connection data required for the HTCP congestion control algorithm"); 178169689Skan 179169689Skanstruct cc_algo htcp_cc_algo = { 180169689Skan .name = "htcp", 181169689Skan .ack_received = htcp_ack_received, 182169689Skan .cb_destroy = htcp_cb_destroy, 183169689Skan .cb_init = htcp_cb_init, 184169689Skan .cong_signal = htcp_cong_signal, 185169689Skan .mod_init = htcp_mod_init, 186169689Skan .post_recovery = htcp_post_recovery, 187169689Skan}; 188169689Skan 189169689Skanstatic void 190169689Skanhtcp_ack_received(struct cc_var *ccv, uint16_t type) 191169689Skan{ 192169689Skan struct htcp *htcp_data; 193169689Skan 194169689Skan htcp_data = ccv->cc_data; 195169689Skan htcp_record_rtt(ccv); 196169689Skan 197169689Skan /* 198169689Skan * Regular ACK and we're not in cong/fast recovery and we're cwnd 199169689Skan * limited and we're either not doing ABC or are slow starting or are 200169689Skan * doing ABC and we've sent a cwnd's worth of bytes. 201169689Skan */ 202169689Skan if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 203169689Skan (ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 || 204169689Skan CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) || 205169689Skan (V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) { 206169689Skan htcp_recalc_beta(ccv); 207169689Skan htcp_recalc_alpha(ccv); 208169689Skan /* 209169689Skan * Use the logic in NewReno ack_received() for slow start and 210169689Skan * for the first HTCP_DELTA_L ticks after either the flow starts 211169689Skan * or a congestion event (when alpha equals 1). 212169689Skan */ 213169689Skan if (htcp_data->alpha == 1 || 214169689Skan CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) 215169689Skan newreno_cc_algo.ack_received(ccv, type); 216169689Skan else { 217169689Skan if (V_tcp_do_rfc3465) { 218169689Skan /* Increment cwnd by alpha segments. */ 219169689Skan CCV(ccv, snd_cwnd) += htcp_data->alpha * 220169689Skan CCV(ccv, t_maxseg); 221169689Skan ccv->flags &= ~CCF_ABC_SENTAWND; 222169689Skan } else 223169689Skan /* 224169689Skan * Increment cwnd by alpha/cwnd segments to 225169689Skan * approximate an increase of alpha segments 226169689Skan * per RTT. 227169689Skan */ 228169689Skan CCV(ccv, snd_cwnd) += (((htcp_data->alpha << 229169689Skan HTCP_SHIFT) / (CCV(ccv, snd_cwnd) / 230169689Skan CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg)) 231169689Skan >> HTCP_SHIFT; 232169689Skan } 233169689Skan } 234169689Skan} 235169689Skan 236169689Skanstatic void 237169689Skanhtcp_cb_destroy(struct cc_var *ccv) 238169689Skan{ 239169689Skan 240169689Skan if (ccv->cc_data != NULL) 241169689Skan free(ccv->cc_data, M_HTCP); 242169689Skan} 243169689Skan 244169689Skanstatic int 245169689Skanhtcp_cb_init(struct cc_var *ccv) 246169689Skan{ 247169689Skan struct htcp *htcp_data; 248169689Skan 249169689Skan htcp_data = malloc(sizeof(struct htcp), M_HTCP, M_NOWAIT); 250169689Skan 251169689Skan if (htcp_data == NULL) 252169689Skan return (ENOMEM); 253169689Skan 254169689Skan /* Init some key variables with sensible defaults. */ 255169689Skan htcp_data->alpha = HTCP_INIT_ALPHA; 256169689Skan htcp_data->beta = HTCP_MINBETA; 257169689Skan htcp_data->maxrtt = TCPTV_SRTTBASE; 258169689Skan htcp_data->minrtt = TCPTV_SRTTBASE; 259169689Skan htcp_data->prev_cwnd = 0; 260169689Skan htcp_data->t_last_cong = ticks; 261169689Skan 262169689Skan ccv->cc_data = htcp_data; 263169689Skan 264169689Skan return (0); 265169689Skan} 266169689Skan 267169689Skan/* 268169689Skan * Perform any necessary tasks before we enter congestion recovery. 269169689Skan */ 270169689Skanstatic void 271169689Skanhtcp_cong_signal(struct cc_var *ccv, uint32_t type) 272169689Skan{ 273169689Skan struct htcp *htcp_data; 274169689Skan 275169689Skan htcp_data = ccv->cc_data; 276169689Skan 277169689Skan switch (type) { 278169689Skan case CC_NDUPACK: 279169689Skan if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 280169689Skan if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 281169689Skan /* 282169689Skan * Apply hysteresis to maxrtt to ensure 283169689Skan * reductions in the RTT are reflected in our 284169689Skan * measurements. 285169689Skan */ 286169689Skan htcp_data->maxrtt = (htcp_data->minrtt + 287169689Skan (htcp_data->maxrtt - htcp_data->minrtt) * 288169689Skan 95) / 100; 289169689Skan htcp_ssthresh_update(ccv); 290169689Skan htcp_data->t_last_cong = ticks; 291169689Skan htcp_data->prev_cwnd = CCV(ccv, snd_cwnd); 292169689Skan } 293169689Skan ENTER_RECOVERY(CCV(ccv, t_flags)); 294169689Skan } 295169689Skan break; 296169689Skan 297169689Skan case CC_ECN: 298169689Skan if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 299169689Skan /* 300169689Skan * Apply hysteresis to maxrtt to ensure reductions in 301169689Skan * the RTT are reflected in our measurements. 302169689Skan */ 303169689Skan htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt - 304169689Skan htcp_data->minrtt) * 95) / 100; 305169689Skan htcp_ssthresh_update(ccv); 306169689Skan CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 307169689Skan htcp_data->t_last_cong = ticks; 308169689Skan htcp_data->prev_cwnd = CCV(ccv, snd_cwnd); 309169689Skan ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 310169689Skan } 311169689Skan break; 312169689Skan 313169689Skan case CC_RTO: 314169689Skan /* 315169689Skan * Grab the current time and record it so we know when the 316169689Skan * most recent congestion event was. Only record it when the 317169689Skan * timeout has fired more than once, as there is a reasonable 318169689Skan * chance the first one is a false alarm and may not indicate 319169689Skan * congestion. 320169689Skan */ 321169689Skan if (CCV(ccv, t_rxtshift) >= 2) 322169689Skan htcp_data->t_last_cong = ticks; 323169689Skan break; 324169689Skan } 325169689Skan} 326169689Skan 327169689Skanstatic int 328169689Skanhtcp_mod_init(void) 329169689Skan{ 330169689Skan 331169689Skan htcp_cc_algo.after_idle = newreno_cc_algo.after_idle; 332169689Skan 333169689Skan /* 334169689Skan * HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in 335169689Skan * units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units 336169689Skan * as t_srtt. 337169689Skan */ 338169689Skan htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000; 339169689Skan 340169689Skan return (0); 341169689Skan} 342169689Skan 343169689Skan/* 344169689Skan * Perform any necessary tasks before we exit congestion recovery. 345169689Skan */ 346169689Skanstatic void 347169689Skanhtcp_post_recovery(struct cc_var *ccv) 348169689Skan{ 349169689Skan int pipe; 350169689Skan struct htcp *htcp_data; 351169689Skan 352169689Skan pipe = 0; 353169689Skan htcp_data = ccv->cc_data; 354169689Skan 355169689Skan if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { 356169689Skan /* 357169689Skan * If inflight data is less than ssthresh, set cwnd 358169689Skan * conservatively to avoid a burst of data, as suggested in the 359169689Skan * NewReno RFC. Otherwise, use the HTCP method. 360169689Skan * 361169689Skan * XXXLAS: Find a way to do this without needing curack 362169689Skan */ 363169689Skan if (V_tcp_do_rfc6675_pipe) 364169689Skan pipe = tcp_compute_pipe(ccv->ccvc.tcp); 365169689Skan else 366169689Skan pipe = CCV(ccv, snd_max) - ccv->curack; 367169689Skan 368169689Skan if (pipe < CCV(ccv, snd_ssthresh)) 369169689Skan CCV(ccv, snd_cwnd) = pipe + CCV(ccv, t_maxseg); 370169689Skan else 371169689Skan CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta * 372169689Skan htcp_data->prev_cwnd / CCV(ccv, t_maxseg)) 373169689Skan >> HTCP_SHIFT)) * CCV(ccv, t_maxseg); 374169689Skan } 375169689Skan} 376169689Skan 377169689Skanstatic void 378169689Skanhtcp_recalc_alpha(struct cc_var *ccv) 379169689Skan{ 380169689Skan struct htcp *htcp_data; 381169689Skan int alpha, diff, now; 382169689Skan 383169689Skan htcp_data = ccv->cc_data; 384169689Skan now = ticks; 385169689Skan 386169689Skan /* 387169689Skan * If ticks has wrapped around (will happen approximately once every 49 388169689Skan * days on a machine with the default kern.hz=1000) and a flow straddles 389169689Skan * the wrap point, our alpha calcs will be completely wrong. We cut our 390169689Skan * losses and restart alpha from scratch by setting t_last_cong = now - 391169689Skan * HTCP_DELTA_L. 392169689Skan * 393169689Skan * This does not deflate our cwnd at all. It simply slows the rate cwnd 394169689Skan * is growing by until alpha regains the value it held prior to taking 395169689Skan * this drastic measure. 396169689Skan */ 397169689Skan if (now < htcp_data->t_last_cong) 398169689Skan htcp_data->t_last_cong = now - HTCP_DELTA_L; 399169689Skan 400169689Skan diff = now - htcp_data->t_last_cong - HTCP_DELTA_L; 401169689Skan 402169689Skan /* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */ 403169689Skan if (diff < htcp_max_diff) { 404169689Skan /* 405169689Skan * If it has been more than HTCP_DELTA_L ticks since congestion, 406169689Skan * increase alpha according to the function defined in the spec. 407169689Skan */ 408169689Skan if (diff > 0) { 409169689Skan alpha = HTCP_CALC_ALPHA(diff); 410169689Skan 411169689Skan /* 412169689Skan * Adaptive backoff fairness adjustment: 413169689Skan * 2 * (1 - beta) * alpha_raw 414169689Skan */ 415169689Skan if (V_htcp_adaptive_backoff) 416169689Skan alpha = max(1, (2 * ((1 << HTCP_SHIFT) - 417169689Skan htcp_data->beta) * alpha) >> HTCP_SHIFT); 418169689Skan 419169689Skan /* 420169689Skan * RTT scaling: (RTT / RTT_ref) * alpha 421169689Skan * alpha will be the raw value from HTCP_CALC_ALPHA() if 422169689Skan * adaptive backoff is off, or the adjusted value if 423169689Skan * adaptive backoff is on. 424169689Skan */ 425169689Skan if (V_htcp_rtt_scaling) 426169689Skan alpha = max(1, (min(max(HTCP_MINROWE, 427169689Skan (CCV(ccv, t_srtt) << HTCP_SHIFT) / 428169689Skan htcp_rtt_ref), HTCP_MAXROWE) * alpha) 429169689Skan >> HTCP_SHIFT); 430169689Skan 431169689Skan } else 432169689Skan alpha = 1; 433169689Skan 434169689Skan htcp_data->alpha = alpha; 435169689Skan } 436169689Skan} 437169689Skan 438169689Skanstatic void 439169689Skanhtcp_recalc_beta(struct cc_var *ccv) 440169689Skan{ 441169689Skan struct htcp *htcp_data; 442 443 htcp_data = ccv->cc_data; 444 445 /* 446 * TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so 447 * we only calc beta if the connection's SRTT has been changed from its 448 * initial value. beta is bounded to ensure it is always between 449 * HTCP_MINBETA and HTCP_MAXBETA. 450 */ 451 if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE && 452 htcp_data->maxrtt != TCPTV_SRTTBASE) 453 htcp_data->beta = min(max(HTCP_MINBETA, 454 (htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt), 455 HTCP_MAXBETA); 456 else 457 htcp_data->beta = HTCP_MINBETA; 458} 459 460/* 461 * Record the minimum and maximum RTT seen for the connection. These are used in 462 * the calculation of beta if adaptive backoff is enabled. 463 */ 464static void 465htcp_record_rtt(struct cc_var *ccv) 466{ 467 struct htcp *htcp_data; 468 469 htcp_data = ccv->cc_data; 470 471 /* XXXLAS: Should there be some hysteresis for minrtt? */ 472 473 /* 474 * Record the current SRTT as our minrtt if it's the smallest we've seen 475 * or minrtt is currently equal to its initialised value. Ignore SRTT 476 * until a min number of samples have been taken. 477 */ 478 if ((CCV(ccv, t_srtt) < htcp_data->minrtt || 479 htcp_data->minrtt == TCPTV_SRTTBASE) && 480 (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)) 481 htcp_data->minrtt = CCV(ccv, t_srtt); 482 483 /* 484 * Record the current SRTT as our maxrtt if it's the largest we've 485 * seen. Ignore SRTT until a min number of samples have been taken. 486 */ 487 if (CCV(ccv, t_srtt) > htcp_data->maxrtt 488 && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES) 489 htcp_data->maxrtt = CCV(ccv, t_srtt); 490} 491 492/* 493 * Update the ssthresh in the event of congestion. 494 */ 495static void 496htcp_ssthresh_update(struct cc_var *ccv) 497{ 498 struct htcp *htcp_data; 499 500 htcp_data = ccv->cc_data; 501 502 /* 503 * On the first congestion event, set ssthresh to cwnd * 0.5, on 504 * subsequent congestion events, set it to cwnd * beta. 505 */ 506 if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT) 507 CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * HTCP_MINBETA) 508 >> HTCP_SHIFT; 509 else { 510 htcp_recalc_beta(ccv); 511 CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * htcp_data->beta) 512 >> HTCP_SHIFT; 513 } 514} 515 516 517SYSCTL_DECL(_net_inet_tcp_cc_htcp); 518SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW, 519 NULL, "H-TCP related settings"); 520SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff, 521 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_adaptive_backoff), 0, 522 "enable H-TCP adaptive backoff"); 523SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling, 524 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_rtt_scaling), 0, 525 "enable H-TCP RTT scaling"); 526 527DECLARE_CC_MODULE(htcp, &htcp_cc_algo); 528