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