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: */
81enum 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 */
89struct 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): */
133static const int bbr_bw_rtts = CYCLE_LEN + 2;
134/* Window length of min_rtt filter (in sec): */
135static const u32 bbr_min_rtt_win_sec = 10;
136/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */
137static const u32 bbr_probe_rtt_mode_ms = 200;
138/* Skip TSO below the following bandwidth (bits/sec): */
139static 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 */
147static 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 */
154static 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 */
158static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
159/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */
160static const int bbr_cwnd_gain = BBR_UNIT * 2;
161/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */
162static 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: */
169static 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 */
175static 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: */
179static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
180/* But after 3 rounds w/o significant bw growth, estimate pipe is full: */
181static 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: */
185static const u32 bbr_lt_intvl_min_rtts = 4;
186/* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */
187static const u32 bbr_lt_loss_thresh = 50;
188/* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */
189static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8;
190/* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */
191static const u32 bbr_lt_bw_diff = 4000 / 8;
192/* If we estimate we're policed, use lt_bw for this many round trips: */
193static const u32 bbr_lt_bw_max_rtts = 48;
194
195/* Gain factor for adding extra_acked to target cwnd: */
196static const int bbr_extra_acked_gain = BBR_UNIT;
197/* Window length of extra_acked window. */
198static const u32 bbr_extra_acked_win_rtts = 5;
199/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */
200static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20;
201/* Time period for clamping cwnd increment due to ack aggregation */
202static const u32 bbr_extra_acked_max_us = 100 * 1000;
203
204static void bbr_check_probe_rtt_done(struct sock *sk);
205
206/* Do we estimate that STARTUP filled the pipe? */
207static 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. */
215static u32 bbr_max_bw(const struct sock *sk)
216{
217 struct bbr *bbr = inet_csk_ca(sk);
218
219 return minmax_get(m: &bbr->bw);
220}
221
222/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */
223static 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 */
233static 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 */
244static 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. */
256static 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. */
266static 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. */
286static 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
304static 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 */
321static 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, bw: 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 */
360static 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 */
395static 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. */
413static 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, cwnd: 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 */
437static 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(dividend: 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 */
457static 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 */
480static 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 */
519static 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, new_cwnd: &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, cwnd: 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
547done:
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. */
554static 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(t1: tp->delivered_mstamp, t0: 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, inflight_now: 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, gain: 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
591static 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. */
601static 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
610static 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
617static 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(ceil: bbr_cycle_rand);
623 bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */
624}
625
626static 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. */
635static 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(dividend: 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. */
647static 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. */
658static 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, rate: 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 */
688static 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(dividend: 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 */
761static 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(seq1: rs->prior_delivered, seq2: 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(m: &bbr->bw, win: bbr_bw_rtts, t: bbr->rtt_cnt, meas: 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 */
817static 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(t1: tp->delivered_mstamp,
841 t0: 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 */
873static 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. */
893static 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, bw: 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, inflight_now: tcp_packets_in_flight(tcp_sk(sk))) <=
904 bbr_inflight(sk, bw: bbr_max_bw(sk), BBR_UNIT))
905 bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */
906}
907
908static 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 */
941static 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(m: 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
987static 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
1016static 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, 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, gain: bbr->pacing_gain);
1036 bbr_set_cwnd(sk, rs, acked: rs->acked_sacked, bw, gain: 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(m: &bbr->bw, t: bbr->rtt_cnt, meas: 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
1107static 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: &rs);
1140 }
1141}
1142
1143static 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
1158BTF_KFUNCS_START(tcp_bbr_check_kfunc_ids)
1159#ifdef CONFIG_X86
1160#ifdef CONFIG_DYNAMIC_FTRACE
1161BTF_ID_FLAGS(func, bbr_init)
1162BTF_ID_FLAGS(func, bbr_main)
1163BTF_ID_FLAGS(func, bbr_sndbuf_expand)
1164BTF_ID_FLAGS(func, bbr_undo_cwnd)
1165BTF_ID_FLAGS(func, bbr_cwnd_event)
1166BTF_ID_FLAGS(func, bbr_ssthresh)
1167BTF_ID_FLAGS(func, bbr_min_tso_segs)
1168BTF_ID_FLAGS(func, bbr_set_state)
1169#endif
1170#endif
1171BTF_KFUNCS_END(tcp_bbr_check_kfunc_ids)
1172
1173static const struct btf_kfunc_id_set tcp_bbr_kfunc_set = {
1174 .owner = THIS_MODULE,
1175 .set = &tcp_bbr_check_kfunc_ids,
1176};
1177
1178static int __init bbr_register(void)
1179{
1180 int ret;
1181
1182 BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
1183
1184 ret = register_btf_kfunc_id_set(prog_type: BPF_PROG_TYPE_STRUCT_OPS, s: &tcp_bbr_kfunc_set);
1185 if (ret < 0)
1186 return ret;
1187 return tcp_register_congestion_control(type: &tcp_bbr_cong_ops);
1188}
1189
1190static void __exit bbr_unregister(void)
1191{
1192 tcp_unregister_congestion_control(type: &tcp_bbr_cong_ops);
1193}
1194
1195module_init(bbr_register);
1196module_exit(bbr_unregister);
1197
1198MODULE_AUTHOR("Van Jacobson <vanj@google.com>");
1199MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>");
1200MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>");
1201MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>");
1202MODULE_LICENSE("Dual BSD/GPL");
1203MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");
1204

source code of linux/net/ipv4/tcp_bbr.c