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(m: &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, 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 | */ |
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, 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 | */ |
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(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 */ |
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, 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 | |
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(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 | |
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(ceil: 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(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. */ |
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, 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 | */ |
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(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 */ |
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(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 | */ |
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(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 | */ |
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, 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 | |
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(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 | |
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, 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 | |
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: &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 | #ifdef CONFIG_X86 |
1160 | #ifdef CONFIG_DYNAMIC_FTRACE |
1161 | BTF_ID_FLAGS(func, bbr_init) |
1162 | BTF_ID_FLAGS(func, bbr_main) |
1163 | BTF_ID_FLAGS(func, bbr_sndbuf_expand) |
1164 | BTF_ID_FLAGS(func, bbr_undo_cwnd) |
1165 | BTF_ID_FLAGS(func, bbr_cwnd_event) |
1166 | BTF_ID_FLAGS(func, bbr_ssthresh) |
1167 | BTF_ID_FLAGS(func, bbr_min_tso_segs) |
1168 | BTF_ID_FLAGS(func, bbr_set_state) |
1169 | #endif |
1170 | #endif |
1171 | BTF_KFUNCS_END(tcp_bbr_check_kfunc_ids) |
1172 | |
1173 | static const struct btf_kfunc_id_set tcp_bbr_kfunc_set = { |
1174 | .owner = THIS_MODULE, |
1175 | .set = &tcp_bbr_check_kfunc_ids, |
1176 | }; |
1177 | |
1178 | static 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 | |
1190 | static void __exit bbr_unregister(void) |
1191 | { |
1192 | tcp_unregister_congestion_control(type: &tcp_bbr_cong_ops); |
1193 | } |
1194 | |
1195 | module_init(bbr_register); |
1196 | module_exit(bbr_unregister); |
1197 | |
1198 | MODULE_AUTHOR("Van Jacobson <vanj@google.com>"); |
1199 | MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>"); |
1200 | MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>"); |
1201 | MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>"); |
1202 | MODULE_LICENSE("Dual BSD/GPL"); |
1203 | MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)"); |
1204 |
Definitions
- bbr_mode
- bbr
- bbr_bw_rtts
- bbr_min_rtt_win_sec
- bbr_probe_rtt_mode_ms
- bbr_min_tso_rate
- bbr_pacing_margin_percent
- bbr_high_gain
- bbr_drain_gain
- bbr_cwnd_gain
- bbr_pacing_gain
- bbr_cycle_rand
- bbr_cwnd_min_target
- bbr_full_bw_thresh
- bbr_full_bw_cnt
- bbr_lt_intvl_min_rtts
- bbr_lt_loss_thresh
- bbr_lt_bw_ratio
- bbr_lt_bw_diff
- bbr_lt_bw_max_rtts
- bbr_extra_acked_gain
- bbr_extra_acked_win_rtts
- bbr_ack_epoch_acked_reset_thresh
- bbr_extra_acked_max_us
- bbr_full_bw_reached
- bbr_max_bw
- bbr_bw
- bbr_extra_acked
- bbr_rate_bytes_per_sec
- bbr_bw_to_pacing_rate
- bbr_init_pacing_rate_from_rtt
- bbr_set_pacing_rate
- bbr_min_tso_segs
- bbr_tso_segs_goal
- bbr_save_cwnd
- bbr_cwnd_event
- bbr_bdp
- bbr_quantization_budget
- bbr_inflight
- bbr_packets_in_net_at_edt
- bbr_ack_aggregation_cwnd
- bbr_set_cwnd_to_recover_or_restore
- bbr_set_cwnd
- bbr_is_next_cycle_phase
- bbr_advance_cycle_phase
- bbr_update_cycle_phase
- bbr_reset_startup_mode
- bbr_reset_probe_bw_mode
- bbr_reset_mode
- bbr_reset_lt_bw_sampling_interval
- bbr_reset_lt_bw_sampling
- bbr_lt_bw_interval_done
- bbr_lt_bw_sampling
- bbr_update_bw
- bbr_update_ack_aggregation
- bbr_check_full_bw_reached
- bbr_check_drain
- bbr_check_probe_rtt_done
- bbr_update_min_rtt
- bbr_update_gains
- bbr_update_model
- bbr_main
- bbr_init
- bbr_sndbuf_expand
- bbr_undo_cwnd
- bbr_ssthresh
- bbr_get_info
- bbr_set_state
- tcp_bbr_cong_ops
- tcp_bbr_check_kfunc_ids
- tcp_bbr_kfunc_set
- bbr_register
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