1 /*- 2 * Copyright (c) 2007-2008 3 * Swinburne University of Technology, Melbourne, Australia 4 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org> 5 * Copyright (c) 2014 Midori Kato <katoon@sfc.wide.ad.jp> 6 * Copyright (c) 2014 The FreeBSD Foundation 7 * All rights reserved. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 */ 30 31 /* 32 * An implementation of the DCTCP algorithm for FreeBSD, based on 33 * "Data Center TCP (DCTCP)" by M. Alizadeh, A. Greenberg, D. A. Maltz, 34 * J. Padhye, P. Patel, B. Prabhakar, S. Sengupta, and M. Sridharan., 35 * in ACM Conference on SIGCOMM 2010, New York, USA, 36 * Originally released as the contribution of Microsoft Research project. 37 */ 38 39 #include <sys/cdefs.h> 40 __FBSDID("$FreeBSD$"); 41 42 #include <sys/param.h> 43 #include <sys/kernel.h> 44 #include <sys/malloc.h> 45 #include <sys/module.h> 46 #include <sys/socket.h> 47 #include <sys/socketvar.h> 48 #include <sys/sysctl.h> 49 #include <sys/systm.h> 50 51 #include <net/vnet.h> 52 53 #include <netinet/tcp.h> 54 #include <netinet/tcp_seq.h> 55 #include <netinet/tcp_var.h> 56 #include <netinet/cc/cc.h> 57 #include <netinet/cc/cc_module.h> 58 59 #define DCTCP_SHIFT 10 60 #define MAX_ALPHA_VALUE (1<<DCTCP_SHIFT) 61 VNET_DEFINE_STATIC(uint32_t, dctcp_alpha) = MAX_ALPHA_VALUE; 62 #define V_dctcp_alpha VNET(dctcp_alpha) 63 VNET_DEFINE_STATIC(uint32_t, dctcp_shift_g) = 4; 64 #define V_dctcp_shift_g VNET(dctcp_shift_g) 65 VNET_DEFINE_STATIC(uint32_t, dctcp_slowstart) = 0; 66 #define V_dctcp_slowstart VNET(dctcp_slowstart) 67 68 struct dctcp { 69 uint32_t bytes_ecn; /* # of marked bytes during a RTT */ 70 uint32_t bytes_total; /* # of acked bytes during a RTT */ 71 int alpha; /* the fraction of marked bytes */ 72 int ce_prev; /* CE state of the last segment */ 73 tcp_seq save_sndnxt; /* end sequence number of the current window */ 74 int ece_curr; /* ECE flag in this segment */ 75 int ece_prev; /* ECE flag in the last segment */ 76 uint32_t num_cong_events; /* # of congestion events */ 77 }; 78 79 static MALLOC_DEFINE(M_dctcp, "dctcp data", 80 "Per connection data required for the dctcp algorithm"); 81 82 static void dctcp_ack_received(struct cc_var *ccv, uint16_t type); 83 static void dctcp_after_idle(struct cc_var *ccv); 84 static void dctcp_cb_destroy(struct cc_var *ccv); 85 static int dctcp_cb_init(struct cc_var *ccv); 86 static void dctcp_cong_signal(struct cc_var *ccv, uint32_t type); 87 static void dctcp_conn_init(struct cc_var *ccv); 88 static void dctcp_post_recovery(struct cc_var *ccv); 89 static void dctcp_ecnpkt_handler(struct cc_var *ccv); 90 static void dctcp_update_alpha(struct cc_var *ccv); 91 92 struct cc_algo dctcp_cc_algo = { 93 .name = "dctcp", 94 .ack_received = dctcp_ack_received, 95 .cb_destroy = dctcp_cb_destroy, 96 .cb_init = dctcp_cb_init, 97 .cong_signal = dctcp_cong_signal, 98 .conn_init = dctcp_conn_init, 99 .post_recovery = dctcp_post_recovery, 100 .ecnpkt_handler = dctcp_ecnpkt_handler, 101 .after_idle = dctcp_after_idle, 102 }; 103 104 static void 105 dctcp_ack_received(struct cc_var *ccv, uint16_t type) 106 { 107 struct dctcp *dctcp_data; 108 int bytes_acked = 0; 109 110 dctcp_data = ccv->cc_data; 111 112 if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) { 113 /* 114 * DCTCP doesn't treat receipt of ECN marked packet as a 115 * congestion event. Thus, DCTCP always executes the ACK 116 * processing out of congestion recovery. 117 */ 118 if (IN_CONGRECOVERY(CCV(ccv, t_flags))) { 119 EXIT_CONGRECOVERY(CCV(ccv, t_flags)); 120 newreno_cc_algo.ack_received(ccv, type); 121 ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 122 } else 123 newreno_cc_algo.ack_received(ccv, type); 124 125 if (type == CC_DUPACK) 126 bytes_acked = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg)); 127 128 if (type == CC_ACK) 129 bytes_acked = ccv->bytes_this_ack; 130 131 /* Update total bytes. */ 132 dctcp_data->bytes_total += bytes_acked; 133 134 /* Update total marked bytes. */ 135 if (dctcp_data->ece_curr) { 136 //XXRMS: For fluid-model DCTCP, update 137 //cwnd here during for RTT fairness 138 if (!dctcp_data->ece_prev 139 && bytes_acked > CCV(ccv, t_maxseg)) { 140 dctcp_data->bytes_ecn += 141 (bytes_acked - CCV(ccv, t_maxseg)); 142 } else 143 dctcp_data->bytes_ecn += bytes_acked; 144 dctcp_data->ece_prev = 1; 145 } else { 146 if (dctcp_data->ece_prev 147 && bytes_acked > CCV(ccv, t_maxseg)) 148 dctcp_data->bytes_ecn += CCV(ccv, t_maxseg); 149 dctcp_data->ece_prev = 0; 150 } 151 dctcp_data->ece_curr = 0; 152 153 /* 154 * Update the fraction of marked bytes at the end of 155 * current window size. 156 */ 157 if (!IN_FASTRECOVERY(CCV(ccv, t_flags)) && 158 SEQ_GT(ccv->curack, dctcp_data->save_sndnxt)) 159 dctcp_update_alpha(ccv); 160 } else 161 newreno_cc_algo.ack_received(ccv, type); 162 } 163 164 static void 165 dctcp_after_idle(struct cc_var *ccv) 166 { 167 struct dctcp *dctcp_data; 168 169 if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) { 170 dctcp_data = ccv->cc_data; 171 172 /* Initialize internal parameters after idle time */ 173 dctcp_data->bytes_ecn = 0; 174 dctcp_data->bytes_total = 0; 175 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt); 176 dctcp_data->alpha = V_dctcp_alpha; 177 dctcp_data->ece_curr = 0; 178 dctcp_data->ece_prev = 0; 179 dctcp_data->num_cong_events = 0; 180 } 181 182 newreno_cc_algo.after_idle(ccv); 183 } 184 185 static void 186 dctcp_cb_destroy(struct cc_var *ccv) 187 { 188 free(ccv->cc_data, M_dctcp); 189 } 190 191 static int 192 dctcp_cb_init(struct cc_var *ccv) 193 { 194 struct dctcp *dctcp_data; 195 196 dctcp_data = malloc(sizeof(struct dctcp), M_dctcp, M_NOWAIT|M_ZERO); 197 198 if (dctcp_data == NULL) 199 return (ENOMEM); 200 201 /* Initialize some key variables with sensible defaults. */ 202 dctcp_data->bytes_ecn = 0; 203 dctcp_data->bytes_total = 0; 204 /* 205 * When alpha is set to 0 in the beginning, DCTCP sender transfers as 206 * much data as possible until the value converges which may expand the 207 * queueing delay at the switch. When alpha is set to 1, queueing delay 208 * is kept small. 209 * Throughput-sensitive applications should have alpha = 0 210 * Latency-sensitive applications should have alpha = 1 211 * 212 * Note: DCTCP draft suggests initial alpha to be 1 but we've decided to 213 * keep it 0 as default. 214 */ 215 dctcp_data->alpha = V_dctcp_alpha; 216 dctcp_data->save_sndnxt = 0; 217 dctcp_data->ce_prev = 0; 218 dctcp_data->ece_curr = 0; 219 dctcp_data->ece_prev = 0; 220 dctcp_data->num_cong_events = 0; 221 222 ccv->cc_data = dctcp_data; 223 return (0); 224 } 225 226 /* 227 * Perform any necessary tasks before we enter congestion recovery. 228 */ 229 static void 230 dctcp_cong_signal(struct cc_var *ccv, uint32_t type) 231 { 232 struct dctcp *dctcp_data; 233 u_int cwin, mss; 234 235 if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) { 236 dctcp_data = ccv->cc_data; 237 cwin = CCV(ccv, snd_cwnd); 238 mss = CCV(ccv, t_maxseg); 239 240 switch (type) { 241 case CC_NDUPACK: 242 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 243 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 244 CCV(ccv, snd_ssthresh) = 245 max(cwin / 2, 2 * mss); 246 dctcp_data->num_cong_events++; 247 } else { 248 /* cwnd has already updated as congestion 249 * recovery. Reverse cwnd value using 250 * snd_cwnd_prev and recalculate snd_ssthresh 251 */ 252 cwin = CCV(ccv, snd_cwnd_prev); 253 CCV(ccv, snd_ssthresh) = 254 max(cwin / 2, 2 * mss); 255 } 256 ENTER_RECOVERY(CCV(ccv, t_flags)); 257 } 258 break; 259 case CC_ECN: 260 /* 261 * Save current snd_cwnd when the host encounters both 262 * congestion recovery and fast recovery. 263 */ 264 CCV(ccv, snd_cwnd_prev) = cwin; 265 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 266 if (V_dctcp_slowstart && 267 dctcp_data->num_cong_events++ == 0) { 268 CCV(ccv, snd_ssthresh) = 269 max(cwin / 2, 2 * mss); 270 dctcp_data->alpha = MAX_ALPHA_VALUE; 271 dctcp_data->bytes_ecn = 0; 272 dctcp_data->bytes_total = 0; 273 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt); 274 } else 275 CCV(ccv, snd_ssthresh) = 276 max((cwin - (((uint64_t)cwin * 277 dctcp_data->alpha) >> (DCTCP_SHIFT+1))), 278 2 * mss); 279 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 280 ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 281 } 282 dctcp_data->ece_curr = 1; 283 break; 284 case CC_RTO: 285 dctcp_update_alpha(ccv); 286 dctcp_data->save_sndnxt += CCV(ccv, t_maxseg); 287 dctcp_data->num_cong_events++; 288 break; 289 } 290 } else 291 newreno_cc_algo.cong_signal(ccv, type); 292 } 293 294 static void 295 dctcp_conn_init(struct cc_var *ccv) 296 { 297 struct dctcp *dctcp_data; 298 299 dctcp_data = ccv->cc_data; 300 301 if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) 302 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt); 303 } 304 305 /* 306 * Perform any necessary tasks before we exit congestion recovery. 307 */ 308 static void 309 dctcp_post_recovery(struct cc_var *ccv) 310 { 311 newreno_cc_algo.post_recovery(ccv); 312 313 if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) 314 dctcp_update_alpha(ccv); 315 } 316 317 /* 318 * Execute an additional ECN processing using ECN field in IP header 319 * and the CWR bit in TCP header. 320 */ 321 static void 322 dctcp_ecnpkt_handler(struct cc_var *ccv) 323 { 324 struct dctcp *dctcp_data; 325 uint32_t ccflag; 326 int acknow; 327 328 dctcp_data = ccv->cc_data; 329 ccflag = ccv->flags; 330 acknow = 0; 331 332 /* 333 * DCTCP responds with an ACK immediately when the CE state 334 * in between this segment and the last segment has changed. 335 */ 336 if (ccflag & CCF_IPHDR_CE) { 337 if (!dctcp_data->ce_prev) { 338 acknow = 1; 339 dctcp_data->ce_prev = 1; 340 CCV(ccv, t_flags2) |= TF2_ECN_SND_ECE; 341 } 342 } else { 343 if (dctcp_data->ce_prev) { 344 acknow = 1; 345 dctcp_data->ce_prev = 0; 346 CCV(ccv, t_flags2) &= ~TF2_ECN_SND_ECE; 347 } 348 } 349 350 if ((acknow) || (ccflag & CCF_TCPHDR_CWR)) { 351 ccv->flags |= CCF_ACKNOW; 352 } else { 353 ccv->flags &= ~CCF_ACKNOW; 354 } 355 } 356 357 /* 358 * Update the fraction of marked bytes represented as 'alpha'. 359 * Also initialize several internal parameters at the end of this function. 360 */ 361 static void 362 dctcp_update_alpha(struct cc_var *ccv) 363 { 364 struct dctcp *dctcp_data; 365 int alpha_prev; 366 367 dctcp_data = ccv->cc_data; 368 alpha_prev = dctcp_data->alpha; 369 dctcp_data->bytes_total = max(dctcp_data->bytes_total, 1); 370 371 /* 372 * Update alpha: alpha = (1 - g) * alpha + g * M. 373 * Here: 374 * g is weight factor 375 * recommaded to be set to 1/16 376 * small g = slow convergence between competitive DCTCP flows 377 * large g = impacts low utilization of bandwidth at switches 378 * M is fraction of marked segments in last RTT 379 * updated every RTT 380 * Alpha must be round to 0 - MAX_ALPHA_VALUE. 381 */ 382 dctcp_data->alpha = ulmin(alpha_prev - (alpha_prev >> V_dctcp_shift_g) + 383 ((uint64_t)dctcp_data->bytes_ecn << (DCTCP_SHIFT - V_dctcp_shift_g)) / 384 dctcp_data->bytes_total, MAX_ALPHA_VALUE); 385 386 /* Initialize internal parameters for next alpha calculation */ 387 dctcp_data->bytes_ecn = 0; 388 dctcp_data->bytes_total = 0; 389 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt); 390 } 391 392 static int 393 dctcp_alpha_handler(SYSCTL_HANDLER_ARGS) 394 { 395 uint32_t new; 396 int error; 397 398 new = V_dctcp_alpha; 399 error = sysctl_handle_int(oidp, &new, 0, req); 400 if (error == 0 && req->newptr != NULL) { 401 if (new > MAX_ALPHA_VALUE) 402 error = EINVAL; 403 else 404 V_dctcp_alpha = new; 405 } 406 407 return (error); 408 } 409 410 static int 411 dctcp_shift_g_handler(SYSCTL_HANDLER_ARGS) 412 { 413 uint32_t new; 414 int error; 415 416 new = V_dctcp_shift_g; 417 error = sysctl_handle_int(oidp, &new, 0, req); 418 if (error == 0 && req->newptr != NULL) { 419 if (new > DCTCP_SHIFT) 420 error = EINVAL; 421 else 422 V_dctcp_shift_g = new; 423 } 424 425 return (error); 426 } 427 428 static int 429 dctcp_slowstart_handler(SYSCTL_HANDLER_ARGS) 430 { 431 uint32_t new; 432 int error; 433 434 new = V_dctcp_slowstart; 435 error = sysctl_handle_int(oidp, &new, 0, req); 436 if (error == 0 && req->newptr != NULL) { 437 if (new > 1) 438 error = EINVAL; 439 else 440 V_dctcp_slowstart = new; 441 } 442 443 return (error); 444 } 445 446 SYSCTL_DECL(_net_inet_tcp_cc_dctcp); 447 SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, dctcp, 448 CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 449 "dctcp congestion control related settings"); 450 451 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, alpha, 452 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 453 &VNET_NAME(dctcp_alpha), 0, &dctcp_alpha_handler, "IU", 454 "dctcp alpha parameter at start of session"); 455 456 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, shift_g, 457 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 458 &VNET_NAME(dctcp_shift_g), 4, &dctcp_shift_g_handler, "IU", 459 "dctcp shift parameter"); 460 461 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart, 462 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 463 &VNET_NAME(dctcp_slowstart), 0, &dctcp_slowstart_handler, "IU", 464 "half CWND reduction after the first slow start"); 465 466 DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo); 467