1 // SPDX-License-Identifier: GPL-2.0 2 /* Bottleneck Bandwidth and RTT (BBR) congestion control 3 * 4 * BBR congestion control computes the sending rate based on the delivery 5 * rate (throughput) estimated from ACKs. In a nutshell: 6 * 7 * On each ACK, update our model of the network path: 8 * bottleneck_bandwidth = windowed_max(delivered / elapsed, 10 round trips) 9 * min_rtt = windowed_min(rtt, 10 seconds) 10 * pacing_rate = pacing_gain * bottleneck_bandwidth 11 * cwnd = max(cwnd_gain * bottleneck_bandwidth * min_rtt, 4) 12 * 13 * The core algorithm does not react directly to packet losses or delays, 14 * although BBR may adjust the size of next send per ACK when loss is 15 * observed, or adjust the sending rate if it estimates there is a 16 * traffic policer, in order to keep the drop rate reasonable. 17 * 18 * Here is a state transition diagram for BBR: 19 * 20 * | 21 * V 22 * +---> STARTUP ----+ 23 * | | | 24 * | V | 25 * | DRAIN ----+ 26 * | | | 27 * | V | 28 * +---> PROBE_BW ----+ 29 * | ^ | | 30 * | | | | 31 * | +----+ | 32 * | | 33 * +---- PROBE_RTT <--+ 34 * 35 * A BBR flow starts in STARTUP, and ramps up its sending rate quickly. 36 * When it estimates the pipe is full, it enters DRAIN to drain the queue. 37 * In steady state a BBR flow only uses PROBE_BW and PROBE_RTT. 38 * A long-lived BBR flow spends the vast majority of its time remaining 39 * (repeatedly) in PROBE_BW, fully probing and utilizing the pipe's bandwidth 40 * in a fair manner, with a small, bounded queue. *If* a flow has been 41 * continuously sending for the entire min_rtt window, and hasn't seen an RTT 42 * sample that matches or decreases its min_rtt estimate for 10 seconds, then 43 * it briefly enters PROBE_RTT to cut inflight to a minimum value to re-probe 44 * the path's two-way propagation delay (min_rtt). When exiting PROBE_RTT, if 45 * we estimated that we reached the full bw of the pipe then we enter PROBE_BW; 46 * otherwise we enter STARTUP to try to fill the pipe. 47 * 48 * BBR is described in detail in: 49 * "BBR: Congestion-Based Congestion Control", 50 * Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas Yeganeh, 51 * Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016. 52 * 53 * There is a public e-mail list for discussing BBR development and testing: 54 * https://groups.google.com/forum/#!forum/bbr-dev 55 * 56 * NOTE: BBR might be used with the fq qdisc ("man tc-fq") with pacing enabled, 57 * otherwise TCP stack falls back to an internal pacing using one high 58 * resolution timer per TCP socket and may use more resources. 59 */ 60 #include <linux/btf.h> 61 #include <linux/btf_ids.h> 62 #include <linux/module.h> 63 #include <net/tcp.h> 64 #include <linux/inet_diag.h> 65 #include <linux/inet.h> 66 #include <linux/random.h> 67 #include <linux/win_minmax.h> 68 69 /* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth 70 * estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps. 71 * This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32. 72 * Since the minimum window is >=4 packets, the lower bound isn't 73 * an issue. The upper bound isn't an issue with existing technologies. 74 */ 75 #define BW_SCALE 24 76 #define BW_UNIT (1 << BW_SCALE) 77 78 #define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */ 79 #define BBR_UNIT (1 << BBR_SCALE) 80 81 /* BBR has the following modes for deciding how fast to send: */ 82 enum bbr_mode { 83 BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */ 84 BBR_DRAIN, /* drain any queue created during startup */ 85 BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */ 86 BBR_PROBE_RTT, /* cut inflight to min to probe min_rtt */ 87 }; 88 89 /* BBR congestion control block */ 90 struct bbr { 91 u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */ 92 u32 min_rtt_stamp; /* timestamp of min_rtt_us */ 93 u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */ 94 struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */ 95 u32 rtt_cnt; /* count of packet-timed rounds elapsed */ 96 u32 next_rtt_delivered; /* scb->tx.delivered at end of round */ 97 u64 cycle_mstamp; /* time of this cycle phase start */ 98 u32 mode:3, /* current bbr_mode in state machine */ 99 prev_ca_state:3, /* CA state on previous ACK */ 100 packet_conservation:1, /* use packet conservation? */ 101 round_start:1, /* start of packet-timed tx->ack round? */ 102 idle_restart:1, /* restarting after idle? */ 103 probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ 104 unused:13, 105 lt_is_sampling:1, /* taking long-term ("LT") samples now? */ 106 lt_rtt_cnt:7, /* round trips in long-term interval */ 107 lt_use_bw:1; /* use lt_bw as our bw estimate? */ 108 u32 lt_bw; /* LT est delivery rate in pkts/uS << 24 */ 109 u32 lt_last_delivered; /* LT intvl start: tp->delivered */ 110 u32 lt_last_stamp; /* LT intvl start: tp->delivered_mstamp */ 111 u32 lt_last_lost; /* LT intvl start: tp->lost */ 112 u32 pacing_gain:10, /* current gain for setting pacing rate */ 113 cwnd_gain:10, /* current gain for setting cwnd */ 114 full_bw_reached:1, /* reached full bw in Startup? */ 115 full_bw_cnt:2, /* number of rounds without large bw gains */ 116 cycle_idx:3, /* current index in pacing_gain cycle array */ 117 has_seen_rtt:1, /* have we seen an RTT sample yet? */ 118 unused_b:5; 119 u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ 120 u32 full_bw; /* recent bw, to estimate if pipe is full */ 121 122 /* For tracking ACK aggregation: */ 123 u64 ack_epoch_mstamp; /* start of ACK sampling epoch */ 124 u16 extra_acked[2]; /* max excess data ACKed in epoch */ 125 u32 ack_epoch_acked:20, /* packets (S)ACKed in sampling epoch */ 126 extra_acked_win_rtts:5, /* age of extra_acked, in round trips */ 127 extra_acked_win_idx:1, /* current index in extra_acked array */ 128 unused_c:6; 129 }; 130 131 #define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ 132 133 /* Window length of bw filter (in rounds): */ 134 static const int bbr_bw_rtts = CYCLE_LEN + 2; 135 /* Window length of min_rtt filter (in sec): */ 136 static const u32 bbr_min_rtt_win_sec = 10; 137 /* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */ 138 static const u32 bbr_probe_rtt_mode_ms = 200; 139 /* Skip TSO below the following bandwidth (bits/sec): */ 140 static const int bbr_min_tso_rate = 1200000; 141 142 /* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck. 143 * In order to help drive the network toward lower queues and low latency while 144 * maintaining high utilization, the average pacing rate aims to be slightly 145 * lower than the estimated bandwidth. This is an important aspect of the 146 * design. 147 */ 148 static const int bbr_pacing_margin_percent = 1; 149 150 /* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain 151 * that will allow a smoothly increasing pacing rate that will double each RTT 152 * and send the same number of packets per RTT that an un-paced, slow-starting 153 * Reno or CUBIC flow would: 154 */ 155 static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1; 156 /* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain 157 * the queue created in BBR_STARTUP in a single round: 158 */ 159 static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885; 160 /* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */ 161 static const int bbr_cwnd_gain = BBR_UNIT * 2; 162 /* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */ 163 static const int bbr_pacing_gain[] = { 164 BBR_UNIT * 5 / 4, /* probe for more available bw */ 165 BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */ 166 BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */ 167 BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */ 168 }; 169 /* Randomize the starting gain cycling phase over N phases: */ 170 static const u32 bbr_cycle_rand = 7; 171 172 /* Try to keep at least this many packets in flight, if things go smoothly. For 173 * smooth functioning, a sliding window protocol ACKing every other packet 174 * needs at least 4 packets in flight: 175 */ 176 static const u32 bbr_cwnd_min_target = 4; 177 178 /* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */ 179 /* If bw has increased significantly (1.25x), there may be more bw available: */ 180 static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4; 181 /* But after 3 rounds w/o significant bw growth, estimate pipe is full: */ 182 static const u32 bbr_full_bw_cnt = 3; 183 184 /* "long-term" ("LT") bandwidth estimator parameters... */ 185 /* The minimum number of rounds in an LT bw sampling interval: */ 186 static const u32 bbr_lt_intvl_min_rtts = 4; 187 /* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */ 188 static const u32 bbr_lt_loss_thresh = 50; 189 /* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */ 190 static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8; 191 /* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */ 192 static const u32 bbr_lt_bw_diff = 4000 / 8; 193 /* If we estimate we're policed, use lt_bw for this many round trips: */ 194 static const u32 bbr_lt_bw_max_rtts = 48; 195 196 /* Gain factor for adding extra_acked to target cwnd: */ 197 static const int bbr_extra_acked_gain = BBR_UNIT; 198 /* Window length of extra_acked window. */ 199 static const u32 bbr_extra_acked_win_rtts = 5; 200 /* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */ 201 static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20; 202 /* Time period for clamping cwnd increment due to ack aggregation */ 203 static const u32 bbr_extra_acked_max_us = 100 * 1000; 204 205 static void bbr_check_probe_rtt_done(struct sock *sk); 206 207 /* Do we estimate that STARTUP filled the pipe? */ 208 static bool bbr_full_bw_reached(const struct sock *sk) 209 { 210 const struct bbr *bbr = inet_csk_ca(sk); 211 212 return bbr->full_bw_reached; 213 } 214 215 /* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */ 216 static u32 bbr_max_bw(const struct sock *sk) 217 { 218 struct bbr *bbr = inet_csk_ca(sk); 219 220 return minmax_get(&bbr->bw); 221 } 222 223 /* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */ 224 static u32 bbr_bw(const struct sock *sk) 225 { 226 struct bbr *bbr = inet_csk_ca(sk); 227 228 return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk); 229 } 230 231 /* Return maximum extra acked in past k-2k round trips, 232 * where k = bbr_extra_acked_win_rtts. 233 */ 234 static u16 bbr_extra_acked(const struct sock *sk) 235 { 236 struct bbr *bbr = inet_csk_ca(sk); 237 238 return max(bbr->extra_acked[0], bbr->extra_acked[1]); 239 } 240 241 /* Return rate in bytes per second, optionally with a gain. 242 * The order here is chosen carefully to avoid overflow of u64. This should 243 * work for input rates of up to 2.9Tbit/sec and gain of 2.89x. 244 */ 245 static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain) 246 { 247 unsigned int mss = tcp_sk(sk)->mss_cache; 248 249 rate *= mss; 250 rate *= gain; 251 rate >>= BBR_SCALE; 252 rate *= USEC_PER_SEC / 100 * (100 - bbr_pacing_margin_percent); 253 return rate >> BW_SCALE; 254 } 255 256 /* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */ 257 static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain) 258 { 259 u64 rate = bw; 260 261 rate = bbr_rate_bytes_per_sec(sk, rate, gain); 262 rate = min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate)); 263 return rate; 264 } 265 266 /* Initialize pacing rate to: high_gain * init_cwnd / RTT. */ 267 static void bbr_init_pacing_rate_from_rtt(struct sock *sk) 268 { 269 struct tcp_sock *tp = tcp_sk(sk); 270 struct bbr *bbr = inet_csk_ca(sk); 271 u64 bw; 272 u32 rtt_us; 273 274 if (tp->srtt_us) { /* any RTT sample yet? */ 275 rtt_us = max(tp->srtt_us >> 3, 1U); 276 bbr->has_seen_rtt = 1; 277 } else { /* no RTT sample yet */ 278 rtt_us = USEC_PER_MSEC; /* use nominal default RTT */ 279 } 280 bw = (u64)tcp_snd_cwnd(tp) * BW_UNIT; 281 do_div(bw, rtt_us); 282 WRITE_ONCE(sk->sk_pacing_rate, 283 bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain)); 284 } 285 286 /* Pace using current bw estimate and a gain factor. */ 287 static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) 288 { 289 struct tcp_sock *tp = tcp_sk(sk); 290 struct bbr *bbr = inet_csk_ca(sk); 291 unsigned long rate = bbr_bw_to_pacing_rate(sk, bw, gain); 292 293 if (unlikely(!bbr->has_seen_rtt && tp->srtt_us)) 294 bbr_init_pacing_rate_from_rtt(sk); 295 if (bbr_full_bw_reached(sk) || rate > READ_ONCE(sk->sk_pacing_rate)) 296 WRITE_ONCE(sk->sk_pacing_rate, rate); 297 } 298 299 /* override sysctl_tcp_min_tso_segs */ 300 __bpf_kfunc static u32 bbr_min_tso_segs(struct sock *sk) 301 { 302 return READ_ONCE(sk->sk_pacing_rate) < (bbr_min_tso_rate >> 3) ? 1 : 2; 303 } 304 305 static u32 bbr_tso_segs_goal(struct sock *sk) 306 { 307 struct tcp_sock *tp = tcp_sk(sk); 308 u32 segs, bytes; 309 310 /* Sort of tcp_tso_autosize() but ignoring 311 * driver provided sk_gso_max_size. 312 */ 313 bytes = min_t(unsigned long, 314 READ_ONCE(sk->sk_pacing_rate) >> READ_ONCE(sk->sk_pacing_shift), 315 GSO_LEGACY_MAX_SIZE - 1 - MAX_TCP_HEADER); 316 segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk)); 317 318 return min(segs, 0x7FU); 319 } 320 321 /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */ 322 static void bbr_save_cwnd(struct sock *sk) 323 { 324 struct tcp_sock *tp = tcp_sk(sk); 325 struct bbr *bbr = inet_csk_ca(sk); 326 327 if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT) 328 bbr->prior_cwnd = tcp_snd_cwnd(tp); /* this cwnd is good enough */ 329 else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */ 330 bbr->prior_cwnd = max(bbr->prior_cwnd, tcp_snd_cwnd(tp)); 331 } 332 333 __bpf_kfunc static void bbr_cwnd_event_tx_start(struct sock *sk) 334 { 335 struct tcp_sock *tp = tcp_sk(sk); 336 struct bbr *bbr = inet_csk_ca(sk); 337 338 if (tp->app_limited) { 339 bbr->idle_restart = 1; 340 bbr->ack_epoch_mstamp = tp->tcp_mstamp; 341 bbr->ack_epoch_acked = 0; 342 /* Avoid pointless buffer overflows: pace at est. bw if we don't 343 * need more speed (we're restarting from idle and app-limited). 344 */ 345 if (bbr->mode == BBR_PROBE_BW) 346 bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); 347 else if (bbr->mode == BBR_PROBE_RTT) 348 bbr_check_probe_rtt_done(sk); 349 } 350 } 351 352 /* Calculate bdp based on min RTT and the estimated bottleneck bandwidth: 353 * 354 * bdp = ceil(bw * min_rtt * gain) 355 * 356 * The key factor, gain, controls the amount of queue. While a small gain 357 * builds a smaller queue, it becomes more vulnerable to noise in RTT 358 * measurements (e.g., delayed ACKs or other ACK compression effects). This 359 * noise may cause BBR to under-estimate the rate. 360 */ 361 static u32 bbr_bdp(struct sock *sk, u32 bw, int gain) 362 { 363 struct bbr *bbr = inet_csk_ca(sk); 364 u32 bdp; 365 u64 w; 366 367 /* If we've never had a valid RTT sample, cap cwnd at the initial 368 * default. This should only happen when the connection is not using TCP 369 * timestamps and has retransmitted all of the SYN/SYNACK/data packets 370 * ACKed so far. In this case, an RTO can cut cwnd to 1, in which 371 * case we need to slow-start up toward something safe: TCP_INIT_CWND. 372 */ 373 if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */ 374 return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/ 375 376 w = (u64)bw * bbr->min_rtt_us; 377 378 /* Apply a gain to the given value, remove the BW_SCALE shift, and 379 * round the value up to avoid a negative feedback loop. 380 */ 381 bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; 382 383 return bdp; 384 } 385 386 /* To achieve full performance in high-speed paths, we budget enough cwnd to 387 * fit full-sized skbs in-flight on both end hosts to fully utilize the path: 388 * - one skb in sending host Qdisc, 389 * - one skb in sending host TSO/GSO engine 390 * - one skb being received by receiver host LRO/GRO/delayed-ACK engine 391 * Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because 392 * in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets, 393 * which allows 2 outstanding 2-packet sequences, to try to keep pipe 394 * full even with ACK-every-other-packet delayed ACKs. 395 */ 396 static u32 bbr_quantization_budget(struct sock *sk, u32 cwnd) 397 { 398 struct bbr *bbr = inet_csk_ca(sk); 399 400 /* Allow enough full-sized skbs in flight to utilize end systems. */ 401 cwnd += 3 * bbr_tso_segs_goal(sk); 402 403 /* Reduce delayed ACKs by rounding up cwnd to the next even number. */ 404 cwnd = (cwnd + 1) & ~1U; 405 406 /* Ensure gain cycling gets inflight above BDP even for small BDPs. */ 407 if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == 0) 408 cwnd += 2; 409 410 return cwnd; 411 } 412 413 /* Find inflight based on min RTT and the estimated bottleneck bandwidth. */ 414 static u32 bbr_inflight(struct sock *sk, u32 bw, int gain) 415 { 416 u32 inflight; 417 418 inflight = bbr_bdp(sk, bw, gain); 419 inflight = bbr_quantization_budget(sk, inflight); 420 421 return inflight; 422 } 423 424 /* With pacing at lower layers, there's often less data "in the network" than 425 * "in flight". With TSQ and departure time pacing at lower layers (e.g. fq), 426 * we often have several skbs queued in the pacing layer with a pre-scheduled 427 * earliest departure time (EDT). BBR adapts its pacing rate based on the 428 * inflight level that it estimates has already been "baked in" by previous 429 * departure time decisions. We calculate a rough estimate of the number of our 430 * packets that might be in the network at the earliest departure time for the 431 * next skb scheduled: 432 * in_network_at_edt = inflight_at_edt - (EDT - now) * bw 433 * If we're increasing inflight, then we want to know if the transmit of the 434 * EDT skb will push inflight above the target, so inflight_at_edt includes 435 * bbr_tso_segs_goal() from the skb departing at EDT. If decreasing inflight, 436 * then estimate if inflight will sink too low just before the EDT transmit. 437 */ 438 static u32 bbr_packets_in_net_at_edt(struct sock *sk, u32 inflight_now) 439 { 440 struct tcp_sock *tp = tcp_sk(sk); 441 struct bbr *bbr = inet_csk_ca(sk); 442 u64 now_ns, edt_ns, interval_us; 443 u32 interval_delivered, inflight_at_edt; 444 445 now_ns = tp->tcp_clock_cache; 446 edt_ns = max(tp->tcp_wstamp_ns, now_ns); 447 interval_us = div_u64(edt_ns - now_ns, NSEC_PER_USEC); 448 interval_delivered = (u64)bbr_bw(sk) * interval_us >> BW_SCALE; 449 inflight_at_edt = inflight_now; 450 if (bbr->pacing_gain > BBR_UNIT) /* increasing inflight */ 451 inflight_at_edt += bbr_tso_segs_goal(sk); /* include EDT skb */ 452 if (interval_delivered >= inflight_at_edt) 453 return 0; 454 return inflight_at_edt - interval_delivered; 455 } 456 457 /* Find the cwnd increment based on estimate of ack aggregation */ 458 static u32 bbr_ack_aggregation_cwnd(struct sock *sk) 459 { 460 u32 max_aggr_cwnd, aggr_cwnd = 0; 461 462 if (bbr_extra_acked_gain && bbr_full_bw_reached(sk)) { 463 max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us) 464 / BW_UNIT; 465 aggr_cwnd = (bbr_extra_acked_gain * bbr_extra_acked(sk)) 466 >> BBR_SCALE; 467 aggr_cwnd = min(aggr_cwnd, max_aggr_cwnd); 468 } 469 470 return aggr_cwnd; 471 } 472 473 /* An optimization in BBR to reduce losses: On the first round of recovery, we 474 * follow the packet conservation principle: send P packets per P packets acked. 475 * After that, we slow-start and send at most 2*P packets per P packets acked. 476 * After recovery finishes, or upon undo, we restore the cwnd we had when 477 * recovery started (capped by the target cwnd based on estimated BDP). 478 * 479 * TODO(ycheng/ncardwell): implement a rate-based approach. 480 */ 481 static bool bbr_set_cwnd_to_recover_or_restore( 482 struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd) 483 { 484 struct tcp_sock *tp = tcp_sk(sk); 485 struct bbr *bbr = inet_csk_ca(sk); 486 u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state; 487 u32 cwnd = tcp_snd_cwnd(tp); 488 489 /* An ACK for P pkts should release at most 2*P packets. We do this 490 * in two steps. First, here we deduct the number of lost packets. 491 * Then, in bbr_set_cwnd() we slow start up toward the target cwnd. 492 */ 493 if (rs->losses > 0) 494 cwnd = max_t(s32, cwnd - rs->losses, 1); 495 496 if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) { 497 /* Starting 1st round of Recovery, so do packet conservation. */ 498 bbr->packet_conservation = 1; 499 bbr->next_rtt_delivered = tp->delivered; /* start round now */ 500 /* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */ 501 cwnd = tcp_packets_in_flight(tp) + acked; 502 } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) { 503 /* Exiting loss recovery; restore cwnd saved before recovery. */ 504 cwnd = max(cwnd, bbr->prior_cwnd); 505 bbr->packet_conservation = 0; 506 } 507 bbr->prev_ca_state = state; 508 509 if (bbr->packet_conservation) { 510 *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked); 511 return true; /* yes, using packet conservation */ 512 } 513 *new_cwnd = cwnd; 514 return false; 515 } 516 517 /* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss 518 * has drawn us down below target), or snap down to target if we're above it. 519 */ 520 static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, 521 u32 acked, u32 bw, int gain) 522 { 523 struct tcp_sock *tp = tcp_sk(sk); 524 struct bbr *bbr = inet_csk_ca(sk); 525 u32 cwnd = tcp_snd_cwnd(tp), target_cwnd = 0; 526 527 if (!acked) 528 goto done; /* no packet fully ACKed; just apply caps */ 529 530 if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) 531 goto done; 532 533 target_cwnd = bbr_bdp(sk, bw, gain); 534 535 /* Increment the cwnd to account for excess ACKed data that seems 536 * due to aggregation (of data and/or ACKs) visible in the ACK stream. 537 */ 538 target_cwnd += bbr_ack_aggregation_cwnd(sk); 539 target_cwnd = bbr_quantization_budget(sk, target_cwnd); 540 541 /* If we're below target cwnd, slow start cwnd toward target cwnd. */ 542 if (bbr_full_bw_reached(sk)) /* only cut cwnd if we filled the pipe */ 543 cwnd = min(cwnd + acked, target_cwnd); 544 else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND) 545 cwnd = cwnd + acked; 546 cwnd = max(cwnd, bbr_cwnd_min_target); 547 548 done: 549 tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp)); /* apply global cap */ 550 if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */ 551 tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), bbr_cwnd_min_target)); 552 } 553 554 /* End cycle phase if it's time and/or we hit the phase's in-flight target. */ 555 static bool bbr_is_next_cycle_phase(struct sock *sk, 556 const struct rate_sample *rs) 557 { 558 struct tcp_sock *tp = tcp_sk(sk); 559 struct bbr *bbr = inet_csk_ca(sk); 560 bool is_full_length = 561 tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp) > 562 bbr->min_rtt_us; 563 u32 inflight, bw; 564 565 /* The pacing_gain of 1.0 paces at the estimated bw to try to fully 566 * use the pipe without increasing the queue. 567 */ 568 if (bbr->pacing_gain == BBR_UNIT) 569 return is_full_length; /* just use wall clock time */ 570 571 inflight = bbr_packets_in_net_at_edt(sk, rs->prior_in_flight); 572 bw = bbr_max_bw(sk); 573 574 /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at 575 * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is 576 * small (e.g. on a LAN). We do not persist if packets are lost, since 577 * a path with small buffers may not hold that much. 578 */ 579 if (bbr->pacing_gain > BBR_UNIT) 580 return is_full_length && 581 (rs->losses || /* perhaps pacing_gain*BDP won't fit */ 582 inflight >= bbr_inflight(sk, bw, bbr->pacing_gain)); 583 584 /* A pacing_gain < 1.0 tries to drain extra queue we added if bw 585 * probing didn't find more bw. If inflight falls to match BDP then we 586 * estimate queue is drained; persisting would underutilize the pipe. 587 */ 588 return is_full_length || 589 inflight <= bbr_inflight(sk, bw, BBR_UNIT); 590 } 591 592 static void bbr_advance_cycle_phase(struct sock *sk) 593 { 594 struct tcp_sock *tp = tcp_sk(sk); 595 struct bbr *bbr = inet_csk_ca(sk); 596 597 bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1); 598 bbr->cycle_mstamp = tp->delivered_mstamp; 599 } 600 601 /* Gain cycling: cycle pacing gain to converge to fair share of available bw. */ 602 static void bbr_update_cycle_phase(struct sock *sk, 603 const struct rate_sample *rs) 604 { 605 struct bbr *bbr = inet_csk_ca(sk); 606 607 if (bbr->mode == BBR_PROBE_BW && bbr_is_next_cycle_phase(sk, rs)) 608 bbr_advance_cycle_phase(sk); 609 } 610 611 static void bbr_reset_startup_mode(struct sock *sk) 612 { 613 struct bbr *bbr = inet_csk_ca(sk); 614 615 bbr->mode = BBR_STARTUP; 616 } 617 618 static void bbr_reset_probe_bw_mode(struct sock *sk) 619 { 620 struct bbr *bbr = inet_csk_ca(sk); 621 622 bbr->mode = BBR_PROBE_BW; 623 bbr->cycle_idx = CYCLE_LEN - 1 - get_random_u32_below(bbr_cycle_rand); 624 bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */ 625 } 626 627 static void bbr_reset_mode(struct sock *sk) 628 { 629 if (!bbr_full_bw_reached(sk)) 630 bbr_reset_startup_mode(sk); 631 else 632 bbr_reset_probe_bw_mode(sk); 633 } 634 635 /* Start a new long-term sampling interval. */ 636 static void bbr_reset_lt_bw_sampling_interval(struct sock *sk) 637 { 638 struct tcp_sock *tp = tcp_sk(sk); 639 struct bbr *bbr = inet_csk_ca(sk); 640 641 bbr->lt_last_stamp = div_u64(tp->delivered_mstamp, USEC_PER_MSEC); 642 bbr->lt_last_delivered = tp->delivered; 643 bbr->lt_last_lost = tp->lost; 644 bbr->lt_rtt_cnt = 0; 645 } 646 647 /* Completely reset long-term bandwidth sampling. */ 648 static void bbr_reset_lt_bw_sampling(struct sock *sk) 649 { 650 struct bbr *bbr = inet_csk_ca(sk); 651 652 bbr->lt_bw = 0; 653 bbr->lt_use_bw = 0; 654 bbr->lt_is_sampling = false; 655 bbr_reset_lt_bw_sampling_interval(sk); 656 } 657 658 /* Long-term bw sampling interval is done. Estimate whether we're policed. */ 659 static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw) 660 { 661 struct bbr *bbr = inet_csk_ca(sk); 662 u32 diff; 663 664 if (bbr->lt_bw) { /* do we have bw from a previous interval? */ 665 /* Is new bw close to the lt_bw from the previous interval? */ 666 diff = abs(bw - bbr->lt_bw); 667 if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) || 668 (bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <= 669 bbr_lt_bw_diff)) { 670 /* All criteria are met; estimate we're policed. */ 671 bbr->lt_bw = (bw + bbr->lt_bw) >> 1; /* avg 2 intvls */ 672 bbr->lt_use_bw = 1; 673 bbr->pacing_gain = BBR_UNIT; /* try to avoid drops */ 674 bbr->lt_rtt_cnt = 0; 675 return; 676 } 677 } 678 bbr->lt_bw = bw; 679 bbr_reset_lt_bw_sampling_interval(sk); 680 } 681 682 /* Token-bucket traffic policers are common (see "An Internet-Wide Analysis of 683 * Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers and 684 * explicitly models their policed rate, to reduce unnecessary losses. We 685 * estimate that we're policed if we see 2 consecutive sampling intervals with 686 * consistent throughput and high packet loss. If we think we're being policed, 687 * set lt_bw to the "long-term" average delivery rate from those 2 intervals. 688 */ 689 static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs) 690 { 691 struct tcp_sock *tp = tcp_sk(sk); 692 struct bbr *bbr = inet_csk_ca(sk); 693 u32 lost, delivered; 694 u64 bw; 695 u32 t; 696 697 if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */ 698 if (bbr->mode == BBR_PROBE_BW && bbr->round_start && 699 ++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) { 700 bbr_reset_lt_bw_sampling(sk); /* stop using lt_bw */ 701 bbr_reset_probe_bw_mode(sk); /* restart gain cycling */ 702 } 703 return; 704 } 705 706 /* Wait for the first loss before sampling, to let the policer exhaust 707 * its tokens and estimate the steady-state rate allowed by the policer. 708 * Starting samples earlier includes bursts that over-estimate the bw. 709 */ 710 if (!bbr->lt_is_sampling) { 711 if (!rs->losses) 712 return; 713 bbr_reset_lt_bw_sampling_interval(sk); 714 bbr->lt_is_sampling = true; 715 } 716 717 /* To avoid underestimates, reset sampling if we run out of data. */ 718 if (rs->is_app_limited) { 719 bbr_reset_lt_bw_sampling(sk); 720 return; 721 } 722 723 if (bbr->round_start) 724 bbr->lt_rtt_cnt++; /* count round trips in this interval */ 725 if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts) 726 return; /* sampling interval needs to be longer */ 727 if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) { 728 bbr_reset_lt_bw_sampling(sk); /* interval is too long */ 729 return; 730 } 731 732 /* End sampling interval when a packet is lost, so we estimate the 733 * policer tokens were exhausted. Stopping the sampling before the 734 * tokens are exhausted under-estimates the policed rate. 735 */ 736 if (!rs->losses) 737 return; 738 739 /* Calculate packets lost and delivered in sampling interval. */ 740 lost = tp->lost - bbr->lt_last_lost; 741 delivered = tp->delivered - bbr->lt_last_delivered; 742 /* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */ 743 if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered) 744 return; 745 746 /* Find average delivery rate in this sampling interval. */ 747 t = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp; 748 if ((s32)t < 1) 749 return; /* interval is less than one ms, so wait */ 750 /* Check if can multiply without overflow */ 751 if (t >= ~0U / USEC_PER_MSEC) { 752 bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */ 753 return; 754 } 755 t *= USEC_PER_MSEC; 756 bw = (u64)delivered * BW_UNIT; 757 do_div(bw, t); 758 bbr_lt_bw_interval_done(sk, bw); 759 } 760 761 /* Estimate the bandwidth based on how fast packets are delivered */ 762 static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs) 763 { 764 struct tcp_sock *tp = tcp_sk(sk); 765 struct bbr *bbr = inet_csk_ca(sk); 766 u64 bw; 767 768 bbr->round_start = 0; 769 if (rs->delivered < 0 || rs->interval_us <= 0) 770 return; /* Not a valid observation */ 771 772 /* See if we've reached the next RTT */ 773 if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) { 774 bbr->next_rtt_delivered = tp->delivered; 775 bbr->rtt_cnt++; 776 bbr->round_start = 1; 777 bbr->packet_conservation = 0; 778 } 779 780 bbr_lt_bw_sampling(sk, rs); 781 782 /* Divide delivered by the interval to find a (lower bound) bottleneck 783 * bandwidth sample. Delivered is in packets and interval_us in uS and 784 * ratio will be <<1 for most connections. So delivered is first scaled. 785 */ 786 bw = div64_long((u64)rs->delivered * BW_UNIT, rs->interval_us); 787 788 /* If this sample is application-limited, it is likely to have a very 789 * low delivered count that represents application behavior rather than 790 * the available network rate. Such a sample could drag down estimated 791 * bw, causing needless slow-down. Thus, to continue to send at the 792 * last measured network rate, we filter out app-limited samples unless 793 * they describe the path bw at least as well as our bw model. 794 * 795 * So the goal during app-limited phase is to proceed with the best 796 * network rate no matter how long. We automatically leave this 797 * phase when app writes faster than the network can deliver :) 798 */ 799 if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) { 800 /* Incorporate new sample into our max bw filter. */ 801 minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw); 802 } 803 } 804 805 /* Estimates the windowed max degree of ack aggregation. 806 * This is used to provision extra in-flight data to keep sending during 807 * inter-ACK silences. 808 * 809 * Degree of ack aggregation is estimated as extra data acked beyond expected. 810 * 811 * max_extra_acked = "maximum recent excess data ACKed beyond max_bw * interval" 812 * cwnd += max_extra_acked 813 * 814 * Max extra_acked is clamped by cwnd and bw * bbr_extra_acked_max_us (100 ms). 815 * Max filter is an approximate sliding window of 5-10 (packet timed) round 816 * trips. 817 */ 818 static void bbr_update_ack_aggregation(struct sock *sk, 819 const struct rate_sample *rs) 820 { 821 u32 epoch_us, expected_acked, extra_acked; 822 struct bbr *bbr = inet_csk_ca(sk); 823 struct tcp_sock *tp = tcp_sk(sk); 824 825 if (!bbr_extra_acked_gain || rs->acked_sacked <= 0 || 826 rs->delivered < 0 || rs->interval_us <= 0) 827 return; 828 829 if (bbr->round_start) { 830 bbr->extra_acked_win_rtts = min(0x1F, 831 bbr->extra_acked_win_rtts + 1); 832 if (bbr->extra_acked_win_rtts >= bbr_extra_acked_win_rtts) { 833 bbr->extra_acked_win_rtts = 0; 834 bbr->extra_acked_win_idx = bbr->extra_acked_win_idx ? 835 0 : 1; 836 bbr->extra_acked[bbr->extra_acked_win_idx] = 0; 837 } 838 } 839 840 /* Compute how many packets we expected to be delivered over epoch. */ 841 epoch_us = tcp_stamp_us_delta(tp->delivered_mstamp, 842 bbr->ack_epoch_mstamp); 843 expected_acked = ((u64)bbr_bw(sk) * epoch_us) / BW_UNIT; 844 845 /* Reset the aggregation epoch if ACK rate is below expected rate or 846 * significantly large no. of ack received since epoch (potentially 847 * quite old epoch). 848 */ 849 if (bbr->ack_epoch_acked <= expected_acked || 850 (bbr->ack_epoch_acked + rs->acked_sacked >= 851 bbr_ack_epoch_acked_reset_thresh)) { 852 bbr->ack_epoch_acked = 0; 853 bbr->ack_epoch_mstamp = tp->delivered_mstamp; 854 expected_acked = 0; 855 } 856 857 /* Compute excess data delivered, beyond what was expected. */ 858 bbr->ack_epoch_acked = min_t(u32, 0xFFFFF, 859 bbr->ack_epoch_acked + rs->acked_sacked); 860 extra_acked = bbr->ack_epoch_acked - expected_acked; 861 extra_acked = min(extra_acked, tcp_snd_cwnd(tp)); 862 if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx]) 863 bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked; 864 } 865 866 /* Estimate when the pipe is full, using the change in delivery rate: BBR 867 * estimates that STARTUP filled the pipe if the estimated bw hasn't changed by 868 * at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited 869 * rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the 870 * higher rwin, 3: we get higher delivery rate samples. Or transient 871 * cross-traffic or radio noise can go away. CUBIC Hystart shares a similar 872 * design goal, but uses delay and inter-ACK spacing instead of bandwidth. 873 */ 874 static void bbr_check_full_bw_reached(struct sock *sk, 875 const struct rate_sample *rs) 876 { 877 struct bbr *bbr = inet_csk_ca(sk); 878 u32 bw_thresh; 879 880 if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited) 881 return; 882 883 bw_thresh = (u64)bbr->full_bw * bbr_full_bw_thresh >> BBR_SCALE; 884 if (bbr_max_bw(sk) >= bw_thresh) { 885 bbr->full_bw = bbr_max_bw(sk); 886 bbr->full_bw_cnt = 0; 887 return; 888 } 889 ++bbr->full_bw_cnt; 890 bbr->full_bw_reached = bbr->full_bw_cnt >= bbr_full_bw_cnt; 891 } 892 893 /* If pipe is probably full, drain the queue and then enter steady-state. */ 894 static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs) 895 { 896 struct bbr *bbr = inet_csk_ca(sk); 897 898 if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) { 899 bbr->mode = BBR_DRAIN; /* drain queue we created */ 900 tcp_sk(sk)->snd_ssthresh = 901 bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT); 902 } /* fall through to check if in-flight is already small: */ 903 if (bbr->mode == BBR_DRAIN && 904 bbr_packets_in_net_at_edt(sk, tcp_packets_in_flight(tcp_sk(sk))) <= 905 bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT)) 906 bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ 907 } 908 909 static void bbr_check_probe_rtt_done(struct sock *sk) 910 { 911 struct tcp_sock *tp = tcp_sk(sk); 912 struct bbr *bbr = inet_csk_ca(sk); 913 914 if (!(bbr->probe_rtt_done_stamp && 915 after(tcp_jiffies32, bbr->probe_rtt_done_stamp))) 916 return; 917 918 bbr->min_rtt_stamp = tcp_jiffies32; /* wait a while until PROBE_RTT */ 919 tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp), bbr->prior_cwnd)); 920 bbr_reset_mode(sk); 921 } 922 923 /* The goal of PROBE_RTT mode is to have BBR flows cooperatively and 924 * periodically drain the bottleneck queue, to converge to measure the true 925 * min_rtt (unloaded propagation delay). This allows the flows to keep queues 926 * small (reducing queuing delay and packet loss) and achieve fairness among 927 * BBR flows. 928 * 929 * The min_rtt filter window is 10 seconds. When the min_rtt estimate expires, 930 * we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets. 931 * After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed 932 * round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and 933 * re-enter the previous mode. BBR uses 200ms to approximately bound the 934 * performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s). 935 * 936 * Note that flows need only pay 2% if they are busy sending over the last 10 937 * seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have 938 * natural silences or low-rate periods within 10 seconds where the rate is low 939 * enough for long enough to drain its queue in the bottleneck. We pick up 940 * these min RTT measurements opportunistically with our min_rtt filter. :-) 941 */ 942 static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) 943 { 944 struct tcp_sock *tp = tcp_sk(sk); 945 struct bbr *bbr = inet_csk_ca(sk); 946 bool filter_expired; 947 948 /* Track min RTT seen in the min_rtt_win_sec filter window: */ 949 filter_expired = after(tcp_jiffies32, 950 bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); 951 if (rs->rtt_us >= 0 && 952 (rs->rtt_us < bbr->min_rtt_us || 953 (filter_expired && !rs->is_ack_delayed))) { 954 bbr->min_rtt_us = rs->rtt_us; 955 bbr->min_rtt_stamp = tcp_jiffies32; 956 } 957 958 if (bbr_probe_rtt_mode_ms > 0 && filter_expired && 959 !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) { 960 bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */ 961 bbr_save_cwnd(sk); /* note cwnd so we can restore it */ 962 bbr->probe_rtt_done_stamp = 0; 963 } 964 965 if (bbr->mode == BBR_PROBE_RTT) { 966 /* Ignore low rate samples during this mode. */ 967 tp->app_limited = 968 (tp->delivered + tcp_packets_in_flight(tp)) ? : 1; 969 /* Maintain min packets in flight for max(200 ms, 1 round). */ 970 if (!bbr->probe_rtt_done_stamp && 971 tcp_packets_in_flight(tp) <= bbr_cwnd_min_target) { 972 bbr->probe_rtt_done_stamp = tcp_jiffies32 + 973 msecs_to_jiffies(bbr_probe_rtt_mode_ms); 974 bbr->probe_rtt_round_done = 0; 975 bbr->next_rtt_delivered = tp->delivered; 976 } else if (bbr->probe_rtt_done_stamp) { 977 if (bbr->round_start) 978 bbr->probe_rtt_round_done = 1; 979 if (bbr->probe_rtt_round_done) 980 bbr_check_probe_rtt_done(sk); 981 } 982 } 983 /* Restart after idle ends only once we process a new S/ACK for data */ 984 if (rs->delivered > 0) 985 bbr->idle_restart = 0; 986 } 987 988 static void bbr_update_gains(struct sock *sk) 989 { 990 struct bbr *bbr = inet_csk_ca(sk); 991 992 switch (bbr->mode) { 993 case BBR_STARTUP: 994 bbr->pacing_gain = bbr_high_gain; 995 bbr->cwnd_gain = bbr_high_gain; 996 break; 997 case BBR_DRAIN: 998 bbr->pacing_gain = bbr_drain_gain; /* slow, to drain */ 999 bbr->cwnd_gain = bbr_high_gain; /* keep cwnd */ 1000 break; 1001 case BBR_PROBE_BW: 1002 bbr->pacing_gain = (bbr->lt_use_bw ? 1003 BBR_UNIT : 1004 bbr_pacing_gain[bbr->cycle_idx]); 1005 bbr->cwnd_gain = bbr_cwnd_gain; 1006 break; 1007 case BBR_PROBE_RTT: 1008 bbr->pacing_gain = BBR_UNIT; 1009 bbr->cwnd_gain = BBR_UNIT; 1010 break; 1011 default: 1012 WARN_ONCE(1, "BBR bad mode: %u\n", bbr->mode); 1013 break; 1014 } 1015 } 1016 1017 static void bbr_update_model(struct sock *sk, const struct rate_sample *rs) 1018 { 1019 bbr_update_bw(sk, rs); 1020 bbr_update_ack_aggregation(sk, rs); 1021 bbr_update_cycle_phase(sk, rs); 1022 bbr_check_full_bw_reached(sk, rs); 1023 bbr_check_drain(sk, rs); 1024 bbr_update_min_rtt(sk, rs); 1025 bbr_update_gains(sk); 1026 } 1027 1028 __bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs) 1029 { 1030 struct bbr *bbr = inet_csk_ca(sk); 1031 u32 bw; 1032 1033 bbr_update_model(sk, rs); 1034 1035 bw = bbr_bw(sk); 1036 bbr_set_pacing_rate(sk, bw, bbr->pacing_gain); 1037 bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain); 1038 } 1039 1040 __bpf_kfunc static void bbr_init(struct sock *sk) 1041 { 1042 struct tcp_sock *tp = tcp_sk(sk); 1043 struct bbr *bbr = inet_csk_ca(sk); 1044 1045 bbr->prior_cwnd = 0; 1046 tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; 1047 bbr->rtt_cnt = 0; 1048 bbr->next_rtt_delivered = tp->delivered; 1049 bbr->prev_ca_state = TCP_CA_Open; 1050 bbr->packet_conservation = 0; 1051 1052 bbr->probe_rtt_done_stamp = 0; 1053 bbr->probe_rtt_round_done = 0; 1054 bbr->min_rtt_us = tcp_min_rtt(tp); 1055 bbr->min_rtt_stamp = tcp_jiffies32; 1056 1057 minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */ 1058 1059 bbr->has_seen_rtt = 0; 1060 bbr_init_pacing_rate_from_rtt(sk); 1061 1062 bbr->round_start = 0; 1063 bbr->idle_restart = 0; 1064 bbr->full_bw_reached = 0; 1065 bbr->full_bw = 0; 1066 bbr->full_bw_cnt = 0; 1067 bbr->cycle_mstamp = 0; 1068 bbr->cycle_idx = 0; 1069 bbr_reset_lt_bw_sampling(sk); 1070 bbr_reset_startup_mode(sk); 1071 1072 bbr->ack_epoch_mstamp = tp->tcp_mstamp; 1073 bbr->ack_epoch_acked = 0; 1074 bbr->extra_acked_win_rtts = 0; 1075 bbr->extra_acked_win_idx = 0; 1076 bbr->extra_acked[0] = 0; 1077 bbr->extra_acked[1] = 0; 1078 1079 cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED); 1080 } 1081 1082 __bpf_kfunc static u32 bbr_sndbuf_expand(struct sock *sk) 1083 { 1084 /* Provision 3 * cwnd since BBR may slow-start even during recovery. */ 1085 return 3; 1086 } 1087 1088 /* In theory BBR does not need to undo the cwnd since it does not 1089 * always reduce cwnd on losses (see bbr_main()). Keep it for now. 1090 */ 1091 __bpf_kfunc static u32 bbr_undo_cwnd(struct sock *sk) 1092 { 1093 struct bbr *bbr = inet_csk_ca(sk); 1094 1095 bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */ 1096 bbr->full_bw_cnt = 0; 1097 bbr_reset_lt_bw_sampling(sk); 1098 return tcp_snd_cwnd(tcp_sk(sk)); 1099 } 1100 1101 /* Entering loss recovery, so save cwnd for when we exit or undo recovery. */ 1102 __bpf_kfunc static u32 bbr_ssthresh(struct sock *sk) 1103 { 1104 bbr_save_cwnd(sk); 1105 return tcp_sk(sk)->snd_ssthresh; 1106 } 1107 1108 static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr, 1109 union tcp_cc_info *info) 1110 { 1111 if (ext & (1 << (INET_DIAG_BBRINFO - 1)) || 1112 ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 1113 struct tcp_sock *tp = tcp_sk(sk); 1114 struct bbr *bbr = inet_csk_ca(sk); 1115 u64 bw = bbr_bw(sk); 1116 1117 bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE; 1118 memset(&info->bbr, 0, sizeof(info->bbr)); 1119 info->bbr.bbr_bw_lo = (u32)bw; 1120 info->bbr.bbr_bw_hi = (u32)(bw >> 32); 1121 info->bbr.bbr_min_rtt = bbr->min_rtt_us; 1122 info->bbr.bbr_pacing_gain = bbr->pacing_gain; 1123 info->bbr.bbr_cwnd_gain = bbr->cwnd_gain; 1124 *attr = INET_DIAG_BBRINFO; 1125 return sizeof(info->bbr); 1126 } 1127 return 0; 1128 } 1129 1130 __bpf_kfunc static void bbr_set_state(struct sock *sk, u8 new_state) 1131 { 1132 struct bbr *bbr = inet_csk_ca(sk); 1133 1134 if (new_state == TCP_CA_Loss) { 1135 struct rate_sample rs = { .losses = 1 }; 1136 1137 bbr->prev_ca_state = TCP_CA_Loss; 1138 bbr->full_bw = 0; 1139 bbr->round_start = 1; /* treat RTO like end of a round */ 1140 bbr_lt_bw_sampling(sk, &rs); 1141 } 1142 } 1143 1144 static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = { 1145 .flags = TCP_CONG_NON_RESTRICTED, 1146 .name = "bbr", 1147 .owner = THIS_MODULE, 1148 .init = bbr_init, 1149 .cong_control = bbr_main, 1150 .sndbuf_expand = bbr_sndbuf_expand, 1151 .undo_cwnd = bbr_undo_cwnd, 1152 .cwnd_event_tx_start = bbr_cwnd_event_tx_start, 1153 .ssthresh = bbr_ssthresh, 1154 .min_tso_segs = bbr_min_tso_segs, 1155 .get_info = bbr_get_info, 1156 .set_state = bbr_set_state, 1157 }; 1158 1159 BTF_KFUNCS_START(tcp_bbr_check_kfunc_ids) 1160 BTF_ID_FLAGS(func, bbr_init) 1161 BTF_ID_FLAGS(func, bbr_main) 1162 BTF_ID_FLAGS(func, bbr_sndbuf_expand) 1163 BTF_ID_FLAGS(func, bbr_undo_cwnd) 1164 BTF_ID_FLAGS(func, bbr_cwnd_event_tx_start) 1165 BTF_ID_FLAGS(func, bbr_ssthresh) 1166 BTF_ID_FLAGS(func, bbr_min_tso_segs) 1167 BTF_ID_FLAGS(func, bbr_set_state) 1168 BTF_KFUNCS_END(tcp_bbr_check_kfunc_ids) 1169 1170 static const struct btf_kfunc_id_set tcp_bbr_kfunc_set = { 1171 .owner = THIS_MODULE, 1172 .set = &tcp_bbr_check_kfunc_ids, 1173 }; 1174 1175 static int __init bbr_register(void) 1176 { 1177 int ret; 1178 1179 BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE); 1180 1181 ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_bbr_kfunc_set); 1182 if (ret < 0) 1183 return ret; 1184 return tcp_register_congestion_control(&tcp_bbr_cong_ops); 1185 } 1186 1187 static void __exit bbr_unregister(void) 1188 { 1189 tcp_unregister_congestion_control(&tcp_bbr_cong_ops); 1190 } 1191 1192 module_init(bbr_register); 1193 module_exit(bbr_unregister); 1194 1195 MODULE_AUTHOR("Van Jacobson <vanj@google.com>"); 1196 MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>"); 1197 MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>"); 1198 MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>"); 1199 MODULE_LICENSE("Dual BSD/GPL"); 1200 MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)"); 1201