1 /* 2 * TCP NV: TCP with Congestion Avoidance 3 * 4 * TCP-NV is a successor of TCP-Vegas that has been developed to 5 * deal with the issues that occur in modern networks. 6 * Like TCP-Vegas, TCP-NV supports true congestion avoidance, 7 * the ability to detect congestion before packet losses occur. 8 * When congestion (queue buildup) starts to occur, TCP-NV 9 * predicts what the cwnd size should be for the current 10 * throughput and it reduces the cwnd proportionally to 11 * the difference between the current cwnd and the predicted cwnd. 12 * 13 * NV is only recommeneded for traffic within a data center, and when 14 * all the flows are NV (at least those within the data center). This 15 * is due to the inherent unfairness between flows using losses to 16 * detect congestion (congestion control) and those that use queue 17 * buildup to detect congestion (congestion avoidance). 18 * 19 * Note: High NIC coalescence values may lower the performance of NV 20 * due to the increased noise in RTT values. In particular, we have 21 * seen issues with rx-frames values greater than 8. 22 * 23 * TODO: 24 * 1) Add mechanism to deal with reverse congestion. 25 */ 26 27 #include <linux/mm.h> 28 #include <linux/module.h> 29 #include <linux/math64.h> 30 #include <net/tcp.h> 31 #include <linux/inet_diag.h> 32 33 /* TCP NV parameters 34 * 35 * nv_pad Max number of queued packets allowed in network 36 * nv_pad_buffer Do not grow cwnd if this closed to nv_pad 37 * nv_reset_period How often (in) seconds)to reset min_rtt 38 * nv_min_cwnd Don't decrease cwnd below this if there are no losses 39 * nv_cong_dec_mult Decrease cwnd by X% (30%) of congestion when detected 40 * nv_ssthresh_factor On congestion set ssthresh to this * <desired cwnd> / 8 41 * nv_rtt_factor RTT averaging factor 42 * nv_loss_dec_factor Decrease cwnd to this (80%) when losses occur 43 * nv_dec_eval_min_calls Wait this many RTT measurements before dec cwnd 44 * nv_inc_eval_min_calls Wait this many RTT measurements before inc cwnd 45 * nv_ssthresh_eval_min_calls Wait this many RTT measurements before stopping 46 * slow-start due to congestion 47 * nv_stop_rtt_cnt Only grow cwnd for this many RTTs after non-congestion 48 * nv_rtt_min_cnt Wait these many RTTs before making congesion decision 49 * nv_cwnd_growth_rate_neg 50 * nv_cwnd_growth_rate_pos 51 * How quickly to double growth rate (not rate) of cwnd when not 52 * congested. One value (nv_cwnd_growth_rate_neg) for when 53 * rate < 1 pkt/RTT (after losses). The other (nv_cwnd_growth_rate_pos) 54 * otherwise. 55 */ 56 57 static int nv_pad __read_mostly = 10; 58 static int nv_pad_buffer __read_mostly = 2; 59 static int nv_reset_period __read_mostly = 5; /* in seconds */ 60 static int nv_min_cwnd __read_mostly = 2; 61 static int nv_cong_dec_mult __read_mostly = 30 * 128 / 100; /* = 30% */ 62 static int nv_ssthresh_factor __read_mostly = 8; /* = 1 */ 63 static int nv_rtt_factor __read_mostly = 128; /* = 1/2*old + 1/2*new */ 64 static int nv_loss_dec_factor __read_mostly = 819; /* => 80% */ 65 static int nv_cwnd_growth_rate_neg __read_mostly = 8; 66 static int nv_cwnd_growth_rate_pos __read_mostly; /* 0 => fixed like Reno */ 67 static int nv_dec_eval_min_calls __read_mostly = 60; 68 static int nv_inc_eval_min_calls __read_mostly = 20; 69 static int nv_ssthresh_eval_min_calls __read_mostly = 30; 70 static int nv_stop_rtt_cnt __read_mostly = 10; 71 static int nv_rtt_min_cnt __read_mostly = 2; 72 73 module_param(nv_pad, int, 0644); 74 MODULE_PARM_DESC(nv_pad, "max queued packets allowed in network"); 75 module_param(nv_reset_period, int, 0644); 76 MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)"); 77 module_param(nv_min_cwnd, int, 0644); 78 MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this value" 79 " without losses"); 80 81 /* TCP NV Parameters */ 82 struct tcpnv { 83 unsigned long nv_min_rtt_reset_jiffies; /* when to switch to 84 * nv_min_rtt_new */ 85 s8 cwnd_growth_factor; /* Current cwnd growth factor, 86 * < 0 => less than 1 packet/RTT */ 87 u8 available8; 88 u16 available16; 89 u8 nv_allow_cwnd_growth:1, /* whether cwnd can grow */ 90 nv_reset:1, /* whether to reset values */ 91 nv_catchup:1; /* whether we are growing because 92 * of temporary cwnd decrease */ 93 u8 nv_eval_call_cnt; /* call count since last eval */ 94 u8 nv_min_cwnd; /* nv won't make a ca decision if cwnd is 95 * smaller than this. It may grow to handle 96 * TSO, LRO and interrupt coalescence because 97 * with these a small cwnd cannot saturate 98 * the link. Note that this is different from 99 * the file local nv_min_cwnd */ 100 u8 nv_rtt_cnt; /* RTTs without making ca decision */; 101 u32 nv_last_rtt; /* last rtt */ 102 u32 nv_min_rtt; /* active min rtt. Used to determine slope */ 103 u32 nv_min_rtt_new; /* min rtt for future use */ 104 u32 nv_base_rtt; /* If non-zero it represents the threshold for 105 * congestion */ 106 u32 nv_lower_bound_rtt; /* Used in conjunction with nv_base_rtt. It is 107 * set to 80% of nv_base_rtt. It helps reduce 108 * unfairness between flows */ 109 u32 nv_rtt_max_rate; /* max rate seen during current RTT */ 110 u32 nv_rtt_start_seq; /* current RTT ends when packet arrives 111 * acking beyond nv_rtt_start_seq */ 112 u32 nv_last_snd_una; /* Previous value of tp->snd_una. It is 113 * used to determine bytes acked since last 114 * call to bictcp_acked */ 115 u32 nv_no_cong_cnt; /* Consecutive no congestion decisions */ 116 }; 117 118 #define NV_INIT_RTT U32_MAX 119 #define NV_MIN_CWND 4 120 #define NV_MIN_CWND_GROW 2 121 #define NV_TSO_CWND_BOUND 80 122 123 static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk) 124 { 125 struct tcp_sock *tp = tcp_sk(sk); 126 127 ca->nv_reset = 0; 128 ca->nv_no_cong_cnt = 0; 129 ca->nv_rtt_cnt = 0; 130 ca->nv_last_rtt = 0; 131 ca->nv_rtt_max_rate = 0; 132 ca->nv_rtt_start_seq = tp->snd_una; 133 ca->nv_eval_call_cnt = 0; 134 ca->nv_last_snd_una = tp->snd_una; 135 } 136 137 static void tcpnv_init(struct sock *sk) 138 { 139 struct tcpnv *ca = inet_csk_ca(sk); 140 int base_rtt; 141 142 tcpnv_reset(ca, sk); 143 144 /* See if base_rtt is available from socket_ops bpf program. 145 * It is meant to be used in environments, such as communication 146 * within a datacenter, where we have reasonable estimates of 147 * RTTs 148 */ 149 base_rtt = tcp_call_bpf(sk, BPF_SOCK_OPS_BASE_RTT, 0, NULL); 150 if (base_rtt > 0) { 151 ca->nv_base_rtt = base_rtt; 152 ca->nv_lower_bound_rtt = (base_rtt * 205) >> 8; /* 80% */ 153 } else { 154 ca->nv_base_rtt = 0; 155 ca->nv_lower_bound_rtt = 0; 156 } 157 158 ca->nv_allow_cwnd_growth = 1; 159 ca->nv_min_rtt_reset_jiffies = jiffies + 2 * HZ; 160 ca->nv_min_rtt = NV_INIT_RTT; 161 ca->nv_min_rtt_new = NV_INIT_RTT; 162 ca->nv_min_cwnd = NV_MIN_CWND; 163 ca->nv_catchup = 0; 164 ca->cwnd_growth_factor = 0; 165 } 166 167 /* If provided, apply upper (base_rtt) and lower (lower_bound_rtt) 168 * bounds to RTT. 169 */ 170 inline u32 nv_get_bounded_rtt(struct tcpnv *ca, u32 val) 171 { 172 if (ca->nv_lower_bound_rtt > 0 && val < ca->nv_lower_bound_rtt) 173 return ca->nv_lower_bound_rtt; 174 else if (ca->nv_base_rtt > 0 && val > ca->nv_base_rtt) 175 return ca->nv_base_rtt; 176 else 177 return val; 178 } 179 180 static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked) 181 { 182 struct tcp_sock *tp = tcp_sk(sk); 183 struct tcpnv *ca = inet_csk_ca(sk); 184 u32 cnt; 185 186 if (!tcp_is_cwnd_limited(sk)) 187 return; 188 189 /* Only grow cwnd if NV has not detected congestion */ 190 if (!ca->nv_allow_cwnd_growth) 191 return; 192 193 if (tcp_in_slow_start(tp)) { 194 acked = tcp_slow_start(tp, acked); 195 if (!acked) 196 return; 197 } 198 199 if (ca->cwnd_growth_factor < 0) { 200 cnt = tp->snd_cwnd << -ca->cwnd_growth_factor; 201 tcp_cong_avoid_ai(tp, cnt, acked); 202 } else { 203 cnt = max(4U, tp->snd_cwnd >> ca->cwnd_growth_factor); 204 tcp_cong_avoid_ai(tp, cnt, acked); 205 } 206 } 207 208 static u32 tcpnv_recalc_ssthresh(struct sock *sk) 209 { 210 const struct tcp_sock *tp = tcp_sk(sk); 211 212 return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U); 213 } 214 215 static void tcpnv_state(struct sock *sk, u8 new_state) 216 { 217 struct tcpnv *ca = inet_csk_ca(sk); 218 219 if (new_state == TCP_CA_Open && ca->nv_reset) { 220 tcpnv_reset(ca, sk); 221 } else if (new_state == TCP_CA_Loss || new_state == TCP_CA_CWR || 222 new_state == TCP_CA_Recovery) { 223 ca->nv_reset = 1; 224 ca->nv_allow_cwnd_growth = 0; 225 if (new_state == TCP_CA_Loss) { 226 /* Reset cwnd growth factor to Reno value */ 227 if (ca->cwnd_growth_factor > 0) 228 ca->cwnd_growth_factor = 0; 229 /* Decrease growth rate if allowed */ 230 if (nv_cwnd_growth_rate_neg > 0 && 231 ca->cwnd_growth_factor > -8) 232 ca->cwnd_growth_factor--; 233 } 234 } 235 } 236 237 /* Do congestion avoidance calculations for TCP-NV 238 */ 239 static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample) 240 { 241 const struct inet_connection_sock *icsk = inet_csk(sk); 242 struct tcp_sock *tp = tcp_sk(sk); 243 struct tcpnv *ca = inet_csk_ca(sk); 244 unsigned long now = jiffies; 245 u64 rate64; 246 u32 rate, max_win, cwnd_by_slope; 247 u32 avg_rtt; 248 u32 bytes_acked = 0; 249 250 /* Some calls are for duplicates without timetamps */ 251 if (sample->rtt_us < 0) 252 return; 253 254 /* If not in TCP_CA_Open or TCP_CA_Disorder states, skip. */ 255 if (icsk->icsk_ca_state != TCP_CA_Open && 256 icsk->icsk_ca_state != TCP_CA_Disorder) 257 return; 258 259 /* Stop cwnd growth if we were in catch up mode */ 260 if (ca->nv_catchup && tp->snd_cwnd >= nv_min_cwnd) { 261 ca->nv_catchup = 0; 262 ca->nv_allow_cwnd_growth = 0; 263 } 264 265 bytes_acked = tp->snd_una - ca->nv_last_snd_una; 266 ca->nv_last_snd_una = tp->snd_una; 267 268 if (sample->in_flight == 0) 269 return; 270 271 /* Calculate moving average of RTT */ 272 if (nv_rtt_factor > 0) { 273 if (ca->nv_last_rtt > 0) { 274 avg_rtt = (((u64)sample->rtt_us) * nv_rtt_factor + 275 ((u64)ca->nv_last_rtt) 276 * (256 - nv_rtt_factor)) >> 8; 277 } else { 278 avg_rtt = sample->rtt_us; 279 ca->nv_min_rtt = avg_rtt << 1; 280 } 281 ca->nv_last_rtt = avg_rtt; 282 } else { 283 avg_rtt = sample->rtt_us; 284 } 285 286 /* rate in 100's bits per second */ 287 rate64 = ((u64)sample->in_flight) * 80000; 288 do_div(rate64, avg_rtt ?: 1); 289 rate = (u32)rate64; 290 291 /* Remember the maximum rate seen during this RTT 292 * Note: It may be more than one RTT. This function should be 293 * called at least nv_dec_eval_min_calls times. 294 */ 295 if (ca->nv_rtt_max_rate < rate) 296 ca->nv_rtt_max_rate = rate; 297 298 /* We have valid information, increment counter */ 299 if (ca->nv_eval_call_cnt < 255) 300 ca->nv_eval_call_cnt++; 301 302 /* Apply bounds to rtt. Only used to update min_rtt */ 303 avg_rtt = nv_get_bounded_rtt(ca, avg_rtt); 304 305 /* update min rtt if necessary */ 306 if (avg_rtt < ca->nv_min_rtt) 307 ca->nv_min_rtt = avg_rtt; 308 309 /* update future min_rtt if necessary */ 310 if (avg_rtt < ca->nv_min_rtt_new) 311 ca->nv_min_rtt_new = avg_rtt; 312 313 /* nv_min_rtt is updated with the minimum (possibley averaged) rtt 314 * seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a 315 * warm reset). This new nv_min_rtt will be continued to be updated 316 * and be used for another sysctl_tcp_nv_reset_period seconds, 317 * when it will be updated again. 318 * In practice we introduce some randomness, so the actual period used 319 * is chosen randomly from the range: 320 * [sysctl_tcp_nv_reset_period*3/4, sysctl_tcp_nv_reset_period*5/4) 321 */ 322 if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) { 323 unsigned char rand; 324 325 ca->nv_min_rtt = ca->nv_min_rtt_new; 326 ca->nv_min_rtt_new = NV_INIT_RTT; 327 get_random_bytes(&rand, 1); 328 ca->nv_min_rtt_reset_jiffies = 329 now + ((nv_reset_period * (384 + rand) * HZ) >> 9); 330 /* Every so often we decrease ca->nv_min_cwnd in case previous 331 * value is no longer accurate. 332 */ 333 ca->nv_min_cwnd = max(ca->nv_min_cwnd / 2, NV_MIN_CWND); 334 } 335 336 /* Once per RTT check if we need to do congestion avoidance */ 337 if (before(ca->nv_rtt_start_seq, tp->snd_una)) { 338 ca->nv_rtt_start_seq = tp->snd_nxt; 339 if (ca->nv_rtt_cnt < 0xff) 340 /* Increase counter for RTTs without CA decision */ 341 ca->nv_rtt_cnt++; 342 343 /* If this function is only called once within an RTT 344 * the cwnd is probably too small (in some cases due to 345 * tso, lro or interrupt coalescence), so we increase 346 * ca->nv_min_cwnd. 347 */ 348 if (ca->nv_eval_call_cnt == 1 && 349 bytes_acked >= (ca->nv_min_cwnd - 1) * tp->mss_cache && 350 ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)) { 351 ca->nv_min_cwnd = min(ca->nv_min_cwnd 352 + NV_MIN_CWND_GROW, 353 NV_TSO_CWND_BOUND + 1); 354 ca->nv_rtt_start_seq = tp->snd_nxt + 355 ca->nv_min_cwnd * tp->mss_cache; 356 ca->nv_eval_call_cnt = 0; 357 ca->nv_allow_cwnd_growth = 1; 358 return; 359 } 360 361 /* Find the ideal cwnd for current rate from slope 362 * slope = 80000.0 * mss / nv_min_rtt 363 * cwnd_by_slope = nv_rtt_max_rate / slope 364 */ 365 cwnd_by_slope = (u32) 366 div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt, 367 80000ULL * tp->mss_cache); 368 max_win = cwnd_by_slope + nv_pad; 369 370 /* If cwnd > max_win, decrease cwnd 371 * if cwnd < max_win, grow cwnd 372 * else leave the same 373 */ 374 if (tp->snd_cwnd > max_win) { 375 /* there is congestion, check that it is ok 376 * to make a CA decision 377 * 1. We should have at least nv_dec_eval_min_calls 378 * data points before making a CA decision 379 * 2. We only make a congesion decision after 380 * nv_rtt_min_cnt RTTs 381 */ 382 if (ca->nv_rtt_cnt < nv_rtt_min_cnt) { 383 return; 384 } else if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) { 385 if (ca->nv_eval_call_cnt < 386 nv_ssthresh_eval_min_calls) 387 return; 388 /* otherwise we will decrease cwnd */ 389 } else if (ca->nv_eval_call_cnt < 390 nv_dec_eval_min_calls) { 391 if (ca->nv_allow_cwnd_growth && 392 ca->nv_rtt_cnt > nv_stop_rtt_cnt) 393 ca->nv_allow_cwnd_growth = 0; 394 return; 395 } 396 397 /* We have enough data to determine we are congested */ 398 ca->nv_allow_cwnd_growth = 0; 399 tp->snd_ssthresh = 400 (nv_ssthresh_factor * max_win) >> 3; 401 if (tp->snd_cwnd - max_win > 2) { 402 /* gap > 2, we do exponential cwnd decrease */ 403 int dec; 404 405 dec = max(2U, ((tp->snd_cwnd - max_win) * 406 nv_cong_dec_mult) >> 7); 407 tp->snd_cwnd -= dec; 408 } else if (nv_cong_dec_mult > 0) { 409 tp->snd_cwnd = max_win; 410 } 411 if (ca->cwnd_growth_factor > 0) 412 ca->cwnd_growth_factor = 0; 413 ca->nv_no_cong_cnt = 0; 414 } else if (tp->snd_cwnd <= max_win - nv_pad_buffer) { 415 /* There is no congestion, grow cwnd if allowed*/ 416 if (ca->nv_eval_call_cnt < nv_inc_eval_min_calls) 417 return; 418 419 ca->nv_allow_cwnd_growth = 1; 420 ca->nv_no_cong_cnt++; 421 if (ca->cwnd_growth_factor < 0 && 422 nv_cwnd_growth_rate_neg > 0 && 423 ca->nv_no_cong_cnt > nv_cwnd_growth_rate_neg) { 424 ca->cwnd_growth_factor++; 425 ca->nv_no_cong_cnt = 0; 426 } else if (ca->cwnd_growth_factor >= 0 && 427 nv_cwnd_growth_rate_pos > 0 && 428 ca->nv_no_cong_cnt > 429 nv_cwnd_growth_rate_pos) { 430 ca->cwnd_growth_factor++; 431 ca->nv_no_cong_cnt = 0; 432 } 433 } else { 434 /* cwnd is in-between, so do nothing */ 435 return; 436 } 437 438 /* update state */ 439 ca->nv_eval_call_cnt = 0; 440 ca->nv_rtt_cnt = 0; 441 ca->nv_rtt_max_rate = 0; 442 443 /* Don't want to make cwnd < nv_min_cwnd 444 * (it wasn't before, if it is now is because nv 445 * decreased it). 446 */ 447 if (tp->snd_cwnd < nv_min_cwnd) 448 tp->snd_cwnd = nv_min_cwnd; 449 } 450 } 451 452 /* Extract info for Tcp socket info provided via netlink */ 453 static size_t tcpnv_get_info(struct sock *sk, u32 ext, int *attr, 454 union tcp_cc_info *info) 455 { 456 const struct tcpnv *ca = inet_csk_ca(sk); 457 458 if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 459 info->vegas.tcpv_enabled = 1; 460 info->vegas.tcpv_rttcnt = ca->nv_rtt_cnt; 461 info->vegas.tcpv_rtt = ca->nv_last_rtt; 462 info->vegas.tcpv_minrtt = ca->nv_min_rtt; 463 464 *attr = INET_DIAG_VEGASINFO; 465 return sizeof(struct tcpvegas_info); 466 } 467 return 0; 468 } 469 470 static struct tcp_congestion_ops tcpnv __read_mostly = { 471 .init = tcpnv_init, 472 .ssthresh = tcpnv_recalc_ssthresh, 473 .cong_avoid = tcpnv_cong_avoid, 474 .set_state = tcpnv_state, 475 .undo_cwnd = tcp_reno_undo_cwnd, 476 .pkts_acked = tcpnv_acked, 477 .get_info = tcpnv_get_info, 478 479 .owner = THIS_MODULE, 480 .name = "nv", 481 }; 482 483 static int __init tcpnv_register(void) 484 { 485 BUILD_BUG_ON(sizeof(struct tcpnv) > ICSK_CA_PRIV_SIZE); 486 487 return tcp_register_congestion_control(&tcpnv); 488 } 489 490 static void __exit tcpnv_unregister(void) 491 { 492 tcp_unregister_congestion_control(&tcpnv); 493 } 494 495 module_init(tcpnv_register); 496 module_exit(tcpnv_unregister); 497 498 MODULE_AUTHOR("Lawrence Brakmo"); 499 MODULE_LICENSE("GPL"); 500 MODULE_DESCRIPTION("TCP NV"); 501 MODULE_VERSION("1.0"); 502