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0f8782ea NC |
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 | * | |
9b9375b5 NC |
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 | * | |
0f8782ea NC |
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 | * | |
218af599 ED |
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. | |
0f8782ea NC |
58 | */ |
59 | #include <linux/module.h> | |
60 | #include <net/tcp.h> | |
61 | #include <linux/inet_diag.h> | |
62 | #include <linux/inet.h> | |
63 | #include <linux/random.h> | |
64 | #include <linux/win_minmax.h> | |
65 | ||
66 | /* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth | |
67 | * estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps. | |
68 | * This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32. | |
69 | * Since the minimum window is >=4 packets, the lower bound isn't | |
70 | * an issue. The upper bound isn't an issue with existing technologies. | |
71 | */ | |
72 | #define BW_SCALE 24 | |
73 | #define BW_UNIT (1 << BW_SCALE) | |
74 | ||
75 | #define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */ | |
76 | #define BBR_UNIT (1 << BBR_SCALE) | |
77 | ||
78 | /* BBR has the following modes for deciding how fast to send: */ | |
79 | enum bbr_mode { | |
80 | BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */ | |
81 | BBR_DRAIN, /* drain any queue created during startup */ | |
82 | BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */ | |
9b9375b5 | 83 | BBR_PROBE_RTT, /* cut inflight to min to probe min_rtt */ |
0f8782ea NC |
84 | }; |
85 | ||
86 | /* BBR congestion control block */ | |
87 | struct bbr { | |
88 | u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */ | |
89 | u32 min_rtt_stamp; /* timestamp of min_rtt_us */ | |
90 | u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */ | |
91 | struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */ | |
92 | u32 rtt_cnt; /* count of packet-timed rounds elapsed */ | |
93 | u32 next_rtt_delivered; /* scb->tx.delivered at end of round */ | |
9a568de4 | 94 | u64 cycle_mstamp; /* time of this cycle phase start */ |
0f8782ea NC |
95 | u32 mode:3, /* current bbr_mode in state machine */ |
96 | prev_ca_state:3, /* CA state on previous ACK */ | |
97 | packet_conservation:1, /* use packet conservation? */ | |
98 | restore_cwnd:1, /* decided to revert cwnd to old value */ | |
99 | round_start:1, /* start of packet-timed tx->ack round? */ | |
100 | tso_segs_goal:7, /* segments we want in each skb we send */ | |
101 | idle_restart:1, /* restarting after idle? */ | |
102 | probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ | |
103 | unused:5, | |
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 */ | |
c589e69b NC |
113 | full_bw_reached:1, /* reached full bw in Startup? */ |
114 | full_bw_cnt:2, /* number of rounds without large bw gains */ | |
0f8782ea | 115 | cycle_idx:3, /* current index in pacing_gain cycle array */ |
32984565 NC |
116 | has_seen_rtt:1, /* have we seen an RTT sample yet? */ |
117 | unused_b:5; | |
0f8782ea NC |
118 | u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ |
119 | u32 full_bw; /* recent bw, to estimate if pipe is full */ | |
120 | }; | |
121 | ||
122 | #define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ | |
123 | ||
124 | /* Window length of bw filter (in rounds): */ | |
125 | static const int bbr_bw_rtts = CYCLE_LEN + 2; | |
126 | /* Window length of min_rtt filter (in sec): */ | |
127 | static const u32 bbr_min_rtt_win_sec = 10; | |
128 | /* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */ | |
129 | static const u32 bbr_probe_rtt_mode_ms = 200; | |
130 | /* Skip TSO below the following bandwidth (bits/sec): */ | |
131 | static const int bbr_min_tso_rate = 1200000; | |
132 | ||
133 | /* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain | |
134 | * that will allow a smoothly increasing pacing rate that will double each RTT | |
135 | * and send the same number of packets per RTT that an un-paced, slow-starting | |
136 | * Reno or CUBIC flow would: | |
137 | */ | |
138 | static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1; | |
139 | /* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain | |
140 | * the queue created in BBR_STARTUP in a single round: | |
141 | */ | |
142 | static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885; | |
143 | /* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */ | |
144 | static const int bbr_cwnd_gain = BBR_UNIT * 2; | |
145 | /* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */ | |
146 | static const int bbr_pacing_gain[] = { | |
147 | BBR_UNIT * 5 / 4, /* probe for more available bw */ | |
148 | BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */ | |
149 | BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */ | |
150 | BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */ | |
151 | }; | |
152 | /* Randomize the starting gain cycling phase over N phases: */ | |
153 | static const u32 bbr_cycle_rand = 7; | |
154 | ||
155 | /* Try to keep at least this many packets in flight, if things go smoothly. For | |
156 | * smooth functioning, a sliding window protocol ACKing every other packet | |
157 | * needs at least 4 packets in flight: | |
158 | */ | |
159 | static const u32 bbr_cwnd_min_target = 4; | |
160 | ||
161 | /* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */ | |
162 | /* If bw has increased significantly (1.25x), there may be more bw available: */ | |
163 | static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4; | |
164 | /* But after 3 rounds w/o significant bw growth, estimate pipe is full: */ | |
165 | static const u32 bbr_full_bw_cnt = 3; | |
166 | ||
167 | /* "long-term" ("LT") bandwidth estimator parameters... */ | |
168 | /* The minimum number of rounds in an LT bw sampling interval: */ | |
169 | static const u32 bbr_lt_intvl_min_rtts = 4; | |
170 | /* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */ | |
171 | static const u32 bbr_lt_loss_thresh = 50; | |
172 | /* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */ | |
173 | static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8; | |
174 | /* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */ | |
175 | static const u32 bbr_lt_bw_diff = 4000 / 8; | |
176 | /* If we estimate we're policed, use lt_bw for this many round trips: */ | |
177 | static const u32 bbr_lt_bw_max_rtts = 48; | |
178 | ||
179 | /* Do we estimate that STARTUP filled the pipe? */ | |
180 | static bool bbr_full_bw_reached(const struct sock *sk) | |
181 | { | |
182 | const struct bbr *bbr = inet_csk_ca(sk); | |
183 | ||
c589e69b | 184 | return bbr->full_bw_reached; |
0f8782ea NC |
185 | } |
186 | ||
187 | /* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */ | |
188 | static u32 bbr_max_bw(const struct sock *sk) | |
189 | { | |
190 | struct bbr *bbr = inet_csk_ca(sk); | |
191 | ||
192 | return minmax_get(&bbr->bw); | |
193 | } | |
194 | ||
195 | /* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */ | |
196 | static u32 bbr_bw(const struct sock *sk) | |
197 | { | |
198 | struct bbr *bbr = inet_csk_ca(sk); | |
199 | ||
200 | return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk); | |
201 | } | |
202 | ||
203 | /* Return rate in bytes per second, optionally with a gain. | |
204 | * The order here is chosen carefully to avoid overflow of u64. This should | |
205 | * work for input rates of up to 2.9Tbit/sec and gain of 2.89x. | |
206 | */ | |
207 | static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain) | |
208 | { | |
209 | rate *= tcp_mss_to_mtu(sk, tcp_sk(sk)->mss_cache); | |
210 | rate *= gain; | |
211 | rate >>= BBR_SCALE; | |
212 | rate *= USEC_PER_SEC; | |
213 | return rate >> BW_SCALE; | |
214 | } | |
215 | ||
f19fd62d NC |
216 | /* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */ |
217 | static u32 bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain) | |
218 | { | |
219 | u64 rate = bw; | |
220 | ||
221 | rate = bbr_rate_bytes_per_sec(sk, rate, gain); | |
222 | rate = min_t(u64, rate, sk->sk_max_pacing_rate); | |
223 | return rate; | |
224 | } | |
225 | ||
79135b89 NC |
226 | /* Initialize pacing rate to: high_gain * init_cwnd / RTT. */ |
227 | static void bbr_init_pacing_rate_from_rtt(struct sock *sk) | |
228 | { | |
229 | struct tcp_sock *tp = tcp_sk(sk); | |
32984565 | 230 | struct bbr *bbr = inet_csk_ca(sk); |
79135b89 NC |
231 | u64 bw; |
232 | u32 rtt_us; | |
233 | ||
234 | if (tp->srtt_us) { /* any RTT sample yet? */ | |
235 | rtt_us = max(tp->srtt_us >> 3, 1U); | |
32984565 | 236 | bbr->has_seen_rtt = 1; |
79135b89 NC |
237 | } else { /* no RTT sample yet */ |
238 | rtt_us = USEC_PER_MSEC; /* use nominal default RTT */ | |
239 | } | |
240 | bw = (u64)tp->snd_cwnd * BW_UNIT; | |
241 | do_div(bw, rtt_us); | |
242 | sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain); | |
243 | } | |
244 | ||
0f8782ea NC |
245 | /* Pace using current bw estimate and a gain factor. In order to help drive the |
246 | * network toward lower queues while maintaining high utilization and low | |
247 | * latency, the average pacing rate aims to be slightly (~1%) lower than the | |
248 | * estimated bandwidth. This is an important aspect of the design. In this | |
249 | * implementation this slightly lower pacing rate is achieved implicitly by not | |
250 | * including link-layer headers in the packet size used for the pacing rate. | |
251 | */ | |
252 | static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) | |
253 | { | |
32984565 NC |
254 | struct tcp_sock *tp = tcp_sk(sk); |
255 | struct bbr *bbr = inet_csk_ca(sk); | |
f19fd62d | 256 | u32 rate = bbr_bw_to_pacing_rate(sk, bw, gain); |
0f8782ea | 257 | |
32984565 NC |
258 | if (unlikely(!bbr->has_seen_rtt && tp->srtt_us)) |
259 | bbr_init_pacing_rate_from_rtt(sk); | |
4aea287e | 260 | if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate) |
0f8782ea NC |
261 | sk->sk_pacing_rate = rate; |
262 | } | |
263 | ||
264 | /* Return count of segments we want in the skbs we send, or 0 for default. */ | |
265 | static u32 bbr_tso_segs_goal(struct sock *sk) | |
266 | { | |
267 | struct bbr *bbr = inet_csk_ca(sk); | |
268 | ||
269 | return bbr->tso_segs_goal; | |
270 | } | |
271 | ||
272 | static void bbr_set_tso_segs_goal(struct sock *sk) | |
273 | { | |
274 | struct tcp_sock *tp = tcp_sk(sk); | |
275 | struct bbr *bbr = inet_csk_ca(sk); | |
276 | u32 min_segs; | |
277 | ||
278 | min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2; | |
279 | bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs), | |
280 | 0x7FU); | |
281 | } | |
282 | ||
283 | /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */ | |
284 | static void bbr_save_cwnd(struct sock *sk) | |
285 | { | |
286 | struct tcp_sock *tp = tcp_sk(sk); | |
287 | struct bbr *bbr = inet_csk_ca(sk); | |
288 | ||
289 | if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT) | |
290 | bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */ | |
291 | else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */ | |
292 | bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd); | |
293 | } | |
294 | ||
295 | static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) | |
296 | { | |
297 | struct tcp_sock *tp = tcp_sk(sk); | |
298 | struct bbr *bbr = inet_csk_ca(sk); | |
299 | ||
300 | if (event == CA_EVENT_TX_START && tp->app_limited) { | |
301 | bbr->idle_restart = 1; | |
302 | /* Avoid pointless buffer overflows: pace at est. bw if we don't | |
303 | * need more speed (we're restarting from idle and app-limited). | |
304 | */ | |
305 | if (bbr->mode == BBR_PROBE_BW) | |
306 | bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); | |
307 | } | |
308 | } | |
309 | ||
310 | /* Find target cwnd. Right-size the cwnd based on min RTT and the | |
311 | * estimated bottleneck bandwidth: | |
312 | * | |
313 | * cwnd = bw * min_rtt * gain = BDP * gain | |
314 | * | |
315 | * The key factor, gain, controls the amount of queue. While a small gain | |
316 | * builds a smaller queue, it becomes more vulnerable to noise in RTT | |
317 | * measurements (e.g., delayed ACKs or other ACK compression effects). This | |
318 | * noise may cause BBR to under-estimate the rate. | |
319 | * | |
320 | * To achieve full performance in high-speed paths, we budget enough cwnd to | |
321 | * fit full-sized skbs in-flight on both end hosts to fully utilize the path: | |
322 | * - one skb in sending host Qdisc, | |
323 | * - one skb in sending host TSO/GSO engine | |
324 | * - one skb being received by receiver host LRO/GRO/delayed-ACK engine | |
325 | * Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because | |
326 | * in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets, | |
327 | * which allows 2 outstanding 2-packet sequences, to try to keep pipe | |
328 | * full even with ACK-every-other-packet delayed ACKs. | |
329 | */ | |
330 | static u32 bbr_target_cwnd(struct sock *sk, u32 bw, int gain) | |
331 | { | |
332 | struct bbr *bbr = inet_csk_ca(sk); | |
333 | u32 cwnd; | |
334 | u64 w; | |
335 | ||
336 | /* If we've never had a valid RTT sample, cap cwnd at the initial | |
337 | * default. This should only happen when the connection is not using TCP | |
338 | * timestamps and has retransmitted all of the SYN/SYNACK/data packets | |
339 | * ACKed so far. In this case, an RTO can cut cwnd to 1, in which | |
340 | * case we need to slow-start up toward something safe: TCP_INIT_CWND. | |
341 | */ | |
342 | if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */ | |
343 | return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/ | |
344 | ||
345 | w = (u64)bw * bbr->min_rtt_us; | |
346 | ||
347 | /* Apply a gain to the given value, then remove the BW_SCALE shift. */ | |
348 | cwnd = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; | |
349 | ||
350 | /* Allow enough full-sized skbs in flight to utilize end systems. */ | |
351 | cwnd += 3 * bbr->tso_segs_goal; | |
352 | ||
353 | /* Reduce delayed ACKs by rounding up cwnd to the next even number. */ | |
354 | cwnd = (cwnd + 1) & ~1U; | |
355 | ||
356 | return cwnd; | |
357 | } | |
358 | ||
359 | /* An optimization in BBR to reduce losses: On the first round of recovery, we | |
360 | * follow the packet conservation principle: send P packets per P packets acked. | |
361 | * After that, we slow-start and send at most 2*P packets per P packets acked. | |
362 | * After recovery finishes, or upon undo, we restore the cwnd we had when | |
363 | * recovery started (capped by the target cwnd based on estimated BDP). | |
364 | * | |
365 | * TODO(ycheng/ncardwell): implement a rate-based approach. | |
366 | */ | |
367 | static bool bbr_set_cwnd_to_recover_or_restore( | |
368 | struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd) | |
369 | { | |
370 | struct tcp_sock *tp = tcp_sk(sk); | |
371 | struct bbr *bbr = inet_csk_ca(sk); | |
372 | u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state; | |
373 | u32 cwnd = tp->snd_cwnd; | |
374 | ||
375 | /* An ACK for P pkts should release at most 2*P packets. We do this | |
376 | * in two steps. First, here we deduct the number of lost packets. | |
377 | * Then, in bbr_set_cwnd() we slow start up toward the target cwnd. | |
378 | */ | |
379 | if (rs->losses > 0) | |
380 | cwnd = max_t(s32, cwnd - rs->losses, 1); | |
381 | ||
382 | if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) { | |
383 | /* Starting 1st round of Recovery, so do packet conservation. */ | |
384 | bbr->packet_conservation = 1; | |
385 | bbr->next_rtt_delivered = tp->delivered; /* start round now */ | |
386 | /* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */ | |
387 | cwnd = tcp_packets_in_flight(tp) + acked; | |
388 | } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) { | |
389 | /* Exiting loss recovery; restore cwnd saved before recovery. */ | |
390 | bbr->restore_cwnd = 1; | |
391 | bbr->packet_conservation = 0; | |
392 | } | |
393 | bbr->prev_ca_state = state; | |
394 | ||
395 | if (bbr->restore_cwnd) { | |
396 | /* Restore cwnd after exiting loss recovery or PROBE_RTT. */ | |
397 | cwnd = max(cwnd, bbr->prior_cwnd); | |
398 | bbr->restore_cwnd = 0; | |
399 | } | |
400 | ||
401 | if (bbr->packet_conservation) { | |
402 | *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked); | |
403 | return true; /* yes, using packet conservation */ | |
404 | } | |
405 | *new_cwnd = cwnd; | |
406 | return false; | |
407 | } | |
408 | ||
409 | /* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss | |
410 | * has drawn us down below target), or snap down to target if we're above it. | |
411 | */ | |
412 | static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, | |
413 | u32 acked, u32 bw, int gain) | |
414 | { | |
415 | struct tcp_sock *tp = tcp_sk(sk); | |
416 | struct bbr *bbr = inet_csk_ca(sk); | |
417 | u32 cwnd = 0, target_cwnd = 0; | |
418 | ||
419 | if (!acked) | |
420 | return; | |
421 | ||
422 | if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) | |
423 | goto done; | |
424 | ||
425 | /* If we're below target cwnd, slow start cwnd toward target cwnd. */ | |
426 | target_cwnd = bbr_target_cwnd(sk, bw, gain); | |
427 | if (bbr_full_bw_reached(sk)) /* only cut cwnd if we filled the pipe */ | |
428 | cwnd = min(cwnd + acked, target_cwnd); | |
429 | else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND) | |
430 | cwnd = cwnd + acked; | |
431 | cwnd = max(cwnd, bbr_cwnd_min_target); | |
432 | ||
433 | done: | |
434 | tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); /* apply global cap */ | |
435 | if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */ | |
436 | tp->snd_cwnd = min(tp->snd_cwnd, bbr_cwnd_min_target); | |
437 | } | |
438 | ||
439 | /* End cycle phase if it's time and/or we hit the phase's in-flight target. */ | |
440 | static bool bbr_is_next_cycle_phase(struct sock *sk, | |
441 | const struct rate_sample *rs) | |
442 | { | |
443 | struct tcp_sock *tp = tcp_sk(sk); | |
444 | struct bbr *bbr = inet_csk_ca(sk); | |
445 | bool is_full_length = | |
9a568de4 | 446 | tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp) > |
0f8782ea NC |
447 | bbr->min_rtt_us; |
448 | u32 inflight, bw; | |
449 | ||
450 | /* The pacing_gain of 1.0 paces at the estimated bw to try to fully | |
451 | * use the pipe without increasing the queue. | |
452 | */ | |
453 | if (bbr->pacing_gain == BBR_UNIT) | |
454 | return is_full_length; /* just use wall clock time */ | |
455 | ||
456 | inflight = rs->prior_in_flight; /* what was in-flight before ACK? */ | |
457 | bw = bbr_max_bw(sk); | |
458 | ||
459 | /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at | |
460 | * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is | |
461 | * small (e.g. on a LAN). We do not persist if packets are lost, since | |
462 | * a path with small buffers may not hold that much. | |
463 | */ | |
464 | if (bbr->pacing_gain > BBR_UNIT) | |
465 | return is_full_length && | |
466 | (rs->losses || /* perhaps pacing_gain*BDP won't fit */ | |
467 | inflight >= bbr_target_cwnd(sk, bw, bbr->pacing_gain)); | |
468 | ||
469 | /* A pacing_gain < 1.0 tries to drain extra queue we added if bw | |
470 | * probing didn't find more bw. If inflight falls to match BDP then we | |
471 | * estimate queue is drained; persisting would underutilize the pipe. | |
472 | */ | |
473 | return is_full_length || | |
474 | inflight <= bbr_target_cwnd(sk, bw, BBR_UNIT); | |
475 | } | |
476 | ||
477 | static void bbr_advance_cycle_phase(struct sock *sk) | |
478 | { | |
479 | struct tcp_sock *tp = tcp_sk(sk); | |
480 | struct bbr *bbr = inet_csk_ca(sk); | |
481 | ||
482 | bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1); | |
483 | bbr->cycle_mstamp = tp->delivered_mstamp; | |
484 | bbr->pacing_gain = bbr_pacing_gain[bbr->cycle_idx]; | |
485 | } | |
486 | ||
487 | /* Gain cycling: cycle pacing gain to converge to fair share of available bw. */ | |
488 | static void bbr_update_cycle_phase(struct sock *sk, | |
489 | const struct rate_sample *rs) | |
490 | { | |
491 | struct bbr *bbr = inet_csk_ca(sk); | |
492 | ||
493 | if ((bbr->mode == BBR_PROBE_BW) && !bbr->lt_use_bw && | |
494 | bbr_is_next_cycle_phase(sk, rs)) | |
495 | bbr_advance_cycle_phase(sk); | |
496 | } | |
497 | ||
498 | static void bbr_reset_startup_mode(struct sock *sk) | |
499 | { | |
500 | struct bbr *bbr = inet_csk_ca(sk); | |
501 | ||
502 | bbr->mode = BBR_STARTUP; | |
503 | bbr->pacing_gain = bbr_high_gain; | |
504 | bbr->cwnd_gain = bbr_high_gain; | |
505 | } | |
506 | ||
507 | static void bbr_reset_probe_bw_mode(struct sock *sk) | |
508 | { | |
509 | struct bbr *bbr = inet_csk_ca(sk); | |
510 | ||
511 | bbr->mode = BBR_PROBE_BW; | |
512 | bbr->pacing_gain = BBR_UNIT; | |
513 | bbr->cwnd_gain = bbr_cwnd_gain; | |
514 | bbr->cycle_idx = CYCLE_LEN - 1 - prandom_u32_max(bbr_cycle_rand); | |
515 | bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */ | |
516 | } | |
517 | ||
518 | static void bbr_reset_mode(struct sock *sk) | |
519 | { | |
520 | if (!bbr_full_bw_reached(sk)) | |
521 | bbr_reset_startup_mode(sk); | |
522 | else | |
523 | bbr_reset_probe_bw_mode(sk); | |
524 | } | |
525 | ||
526 | /* Start a new long-term sampling interval. */ | |
527 | static void bbr_reset_lt_bw_sampling_interval(struct sock *sk) | |
528 | { | |
529 | struct tcp_sock *tp = tcp_sk(sk); | |
530 | struct bbr *bbr = inet_csk_ca(sk); | |
531 | ||
9a568de4 | 532 | bbr->lt_last_stamp = div_u64(tp->delivered_mstamp, USEC_PER_MSEC); |
0f8782ea NC |
533 | bbr->lt_last_delivered = tp->delivered; |
534 | bbr->lt_last_lost = tp->lost; | |
535 | bbr->lt_rtt_cnt = 0; | |
536 | } | |
537 | ||
538 | /* Completely reset long-term bandwidth sampling. */ | |
539 | static void bbr_reset_lt_bw_sampling(struct sock *sk) | |
540 | { | |
541 | struct bbr *bbr = inet_csk_ca(sk); | |
542 | ||
543 | bbr->lt_bw = 0; | |
544 | bbr->lt_use_bw = 0; | |
545 | bbr->lt_is_sampling = false; | |
546 | bbr_reset_lt_bw_sampling_interval(sk); | |
547 | } | |
548 | ||
549 | /* Long-term bw sampling interval is done. Estimate whether we're policed. */ | |
550 | static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw) | |
551 | { | |
552 | struct bbr *bbr = inet_csk_ca(sk); | |
553 | u32 diff; | |
554 | ||
555 | if (bbr->lt_bw) { /* do we have bw from a previous interval? */ | |
556 | /* Is new bw close to the lt_bw from the previous interval? */ | |
557 | diff = abs(bw - bbr->lt_bw); | |
558 | if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) || | |
559 | (bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <= | |
560 | bbr_lt_bw_diff)) { | |
561 | /* All criteria are met; estimate we're policed. */ | |
562 | bbr->lt_bw = (bw + bbr->lt_bw) >> 1; /* avg 2 intvls */ | |
563 | bbr->lt_use_bw = 1; | |
564 | bbr->pacing_gain = BBR_UNIT; /* try to avoid drops */ | |
565 | bbr->lt_rtt_cnt = 0; | |
566 | return; | |
567 | } | |
568 | } | |
569 | bbr->lt_bw = bw; | |
570 | bbr_reset_lt_bw_sampling_interval(sk); | |
571 | } | |
572 | ||
573 | /* Token-bucket traffic policers are common (see "An Internet-Wide Analysis of | |
574 | * Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers and | |
575 | * explicitly models their policed rate, to reduce unnecessary losses. We | |
576 | * estimate that we're policed if we see 2 consecutive sampling intervals with | |
577 | * consistent throughput and high packet loss. If we think we're being policed, | |
578 | * set lt_bw to the "long-term" average delivery rate from those 2 intervals. | |
579 | */ | |
580 | static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs) | |
581 | { | |
582 | struct tcp_sock *tp = tcp_sk(sk); | |
583 | struct bbr *bbr = inet_csk_ca(sk); | |
584 | u32 lost, delivered; | |
585 | u64 bw; | |
9a568de4 | 586 | u32 t; |
0f8782ea NC |
587 | |
588 | if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */ | |
589 | if (bbr->mode == BBR_PROBE_BW && bbr->round_start && | |
590 | ++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) { | |
591 | bbr_reset_lt_bw_sampling(sk); /* stop using lt_bw */ | |
592 | bbr_reset_probe_bw_mode(sk); /* restart gain cycling */ | |
593 | } | |
594 | return; | |
595 | } | |
596 | ||
597 | /* Wait for the first loss before sampling, to let the policer exhaust | |
598 | * its tokens and estimate the steady-state rate allowed by the policer. | |
599 | * Starting samples earlier includes bursts that over-estimate the bw. | |
600 | */ | |
601 | if (!bbr->lt_is_sampling) { | |
602 | if (!rs->losses) | |
603 | return; | |
604 | bbr_reset_lt_bw_sampling_interval(sk); | |
605 | bbr->lt_is_sampling = true; | |
606 | } | |
607 | ||
608 | /* To avoid underestimates, reset sampling if we run out of data. */ | |
609 | if (rs->is_app_limited) { | |
610 | bbr_reset_lt_bw_sampling(sk); | |
611 | return; | |
612 | } | |
613 | ||
614 | if (bbr->round_start) | |
615 | bbr->lt_rtt_cnt++; /* count round trips in this interval */ | |
616 | if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts) | |
617 | return; /* sampling interval needs to be longer */ | |
618 | if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) { | |
619 | bbr_reset_lt_bw_sampling(sk); /* interval is too long */ | |
620 | return; | |
621 | } | |
622 | ||
623 | /* End sampling interval when a packet is lost, so we estimate the | |
624 | * policer tokens were exhausted. Stopping the sampling before the | |
625 | * tokens are exhausted under-estimates the policed rate. | |
626 | */ | |
627 | if (!rs->losses) | |
628 | return; | |
629 | ||
630 | /* Calculate packets lost and delivered in sampling interval. */ | |
631 | lost = tp->lost - bbr->lt_last_lost; | |
632 | delivered = tp->delivered - bbr->lt_last_delivered; | |
633 | /* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */ | |
634 | if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered) | |
635 | return; | |
636 | ||
637 | /* Find average delivery rate in this sampling interval. */ | |
9a568de4 ED |
638 | t = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp; |
639 | if ((s32)t < 1) | |
640 | return; /* interval is less than one ms, so wait */ | |
641 | /* Check if can multiply without overflow */ | |
642 | if (t >= ~0U / USEC_PER_MSEC) { | |
0f8782ea NC |
643 | bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */ |
644 | return; | |
645 | } | |
9a568de4 | 646 | t *= USEC_PER_MSEC; |
0f8782ea NC |
647 | bw = (u64)delivered * BW_UNIT; |
648 | do_div(bw, t); | |
649 | bbr_lt_bw_interval_done(sk, bw); | |
650 | } | |
651 | ||
652 | /* Estimate the bandwidth based on how fast packets are delivered */ | |
653 | static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs) | |
654 | { | |
655 | struct tcp_sock *tp = tcp_sk(sk); | |
656 | struct bbr *bbr = inet_csk_ca(sk); | |
657 | u64 bw; | |
658 | ||
659 | bbr->round_start = 0; | |
660 | if (rs->delivered < 0 || rs->interval_us <= 0) | |
661 | return; /* Not a valid observation */ | |
662 | ||
663 | /* See if we've reached the next RTT */ | |
664 | if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) { | |
665 | bbr->next_rtt_delivered = tp->delivered; | |
666 | bbr->rtt_cnt++; | |
667 | bbr->round_start = 1; | |
668 | bbr->packet_conservation = 0; | |
669 | } | |
670 | ||
671 | bbr_lt_bw_sampling(sk, rs); | |
672 | ||
673 | /* Divide delivered by the interval to find a (lower bound) bottleneck | |
674 | * bandwidth sample. Delivered is in packets and interval_us in uS and | |
675 | * ratio will be <<1 for most connections. So delivered is first scaled. | |
676 | */ | |
677 | bw = (u64)rs->delivered * BW_UNIT; | |
678 | do_div(bw, rs->interval_us); | |
679 | ||
680 | /* If this sample is application-limited, it is likely to have a very | |
681 | * low delivered count that represents application behavior rather than | |
682 | * the available network rate. Such a sample could drag down estimated | |
683 | * bw, causing needless slow-down. Thus, to continue to send at the | |
684 | * last measured network rate, we filter out app-limited samples unless | |
685 | * they describe the path bw at least as well as our bw model. | |
686 | * | |
687 | * So the goal during app-limited phase is to proceed with the best | |
688 | * network rate no matter how long. We automatically leave this | |
689 | * phase when app writes faster than the network can deliver :) | |
690 | */ | |
691 | if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) { | |
692 | /* Incorporate new sample into our max bw filter. */ | |
693 | minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw); | |
694 | } | |
695 | } | |
696 | ||
697 | /* Estimate when the pipe is full, using the change in delivery rate: BBR | |
698 | * estimates that STARTUP filled the pipe if the estimated bw hasn't changed by | |
699 | * at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited | |
700 | * rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the | |
701 | * higher rwin, 3: we get higher delivery rate samples. Or transient | |
702 | * cross-traffic or radio noise can go away. CUBIC Hystart shares a similar | |
703 | * design goal, but uses delay and inter-ACK spacing instead of bandwidth. | |
704 | */ | |
705 | static void bbr_check_full_bw_reached(struct sock *sk, | |
706 | const struct rate_sample *rs) | |
707 | { | |
708 | struct bbr *bbr = inet_csk_ca(sk); | |
709 | u32 bw_thresh; | |
710 | ||
711 | if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited) | |
712 | return; | |
713 | ||
714 | bw_thresh = (u64)bbr->full_bw * bbr_full_bw_thresh >> BBR_SCALE; | |
715 | if (bbr_max_bw(sk) >= bw_thresh) { | |
716 | bbr->full_bw = bbr_max_bw(sk); | |
717 | bbr->full_bw_cnt = 0; | |
718 | return; | |
719 | } | |
720 | ++bbr->full_bw_cnt; | |
c589e69b | 721 | bbr->full_bw_reached = bbr->full_bw_cnt >= bbr_full_bw_cnt; |
0f8782ea NC |
722 | } |
723 | ||
724 | /* If pipe is probably full, drain the queue and then enter steady-state. */ | |
725 | static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs) | |
726 | { | |
727 | struct bbr *bbr = inet_csk_ca(sk); | |
728 | ||
729 | if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) { | |
730 | bbr->mode = BBR_DRAIN; /* drain queue we created */ | |
731 | bbr->pacing_gain = bbr_drain_gain; /* pace slow to drain */ | |
732 | bbr->cwnd_gain = bbr_high_gain; /* maintain cwnd */ | |
733 | } /* fall through to check if in-flight is already small: */ | |
734 | if (bbr->mode == BBR_DRAIN && | |
735 | tcp_packets_in_flight(tcp_sk(sk)) <= | |
736 | bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT)) | |
737 | bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ | |
738 | } | |
739 | ||
740 | /* The goal of PROBE_RTT mode is to have BBR flows cooperatively and | |
741 | * periodically drain the bottleneck queue, to converge to measure the true | |
742 | * min_rtt (unloaded propagation delay). This allows the flows to keep queues | |
743 | * small (reducing queuing delay and packet loss) and achieve fairness among | |
744 | * BBR flows. | |
745 | * | |
746 | * The min_rtt filter window is 10 seconds. When the min_rtt estimate expires, | |
747 | * we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets. | |
748 | * After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed | |
749 | * round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and | |
750 | * re-enter the previous mode. BBR uses 200ms to approximately bound the | |
751 | * performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s). | |
752 | * | |
753 | * Note that flows need only pay 2% if they are busy sending over the last 10 | |
754 | * seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have | |
755 | * natural silences or low-rate periods within 10 seconds where the rate is low | |
756 | * enough for long enough to drain its queue in the bottleneck. We pick up | |
757 | * these min RTT measurements opportunistically with our min_rtt filter. :-) | |
758 | */ | |
759 | static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) | |
760 | { | |
761 | struct tcp_sock *tp = tcp_sk(sk); | |
762 | struct bbr *bbr = inet_csk_ca(sk); | |
763 | bool filter_expired; | |
764 | ||
765 | /* Track min RTT seen in the min_rtt_win_sec filter window: */ | |
2660bfa8 | 766 | filter_expired = after(tcp_jiffies32, |
0f8782ea NC |
767 | bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); |
768 | if (rs->rtt_us >= 0 && | |
769 | (rs->rtt_us <= bbr->min_rtt_us || filter_expired)) { | |
770 | bbr->min_rtt_us = rs->rtt_us; | |
2660bfa8 | 771 | bbr->min_rtt_stamp = tcp_jiffies32; |
0f8782ea NC |
772 | } |
773 | ||
774 | if (bbr_probe_rtt_mode_ms > 0 && filter_expired && | |
775 | !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) { | |
776 | bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */ | |
777 | bbr->pacing_gain = BBR_UNIT; | |
778 | bbr->cwnd_gain = BBR_UNIT; | |
779 | bbr_save_cwnd(sk); /* note cwnd so we can restore it */ | |
780 | bbr->probe_rtt_done_stamp = 0; | |
781 | } | |
782 | ||
783 | if (bbr->mode == BBR_PROBE_RTT) { | |
784 | /* Ignore low rate samples during this mode. */ | |
785 | tp->app_limited = | |
786 | (tp->delivered + tcp_packets_in_flight(tp)) ? : 1; | |
787 | /* Maintain min packets in flight for max(200 ms, 1 round). */ | |
788 | if (!bbr->probe_rtt_done_stamp && | |
789 | tcp_packets_in_flight(tp) <= bbr_cwnd_min_target) { | |
2660bfa8 | 790 | bbr->probe_rtt_done_stamp = tcp_jiffies32 + |
0f8782ea NC |
791 | msecs_to_jiffies(bbr_probe_rtt_mode_ms); |
792 | bbr->probe_rtt_round_done = 0; | |
793 | bbr->next_rtt_delivered = tp->delivered; | |
794 | } else if (bbr->probe_rtt_done_stamp) { | |
795 | if (bbr->round_start) | |
796 | bbr->probe_rtt_round_done = 1; | |
797 | if (bbr->probe_rtt_round_done && | |
2660bfa8 ED |
798 | after(tcp_jiffies32, bbr->probe_rtt_done_stamp)) { |
799 | bbr->min_rtt_stamp = tcp_jiffies32; | |
0f8782ea NC |
800 | bbr->restore_cwnd = 1; /* snap to prior_cwnd */ |
801 | bbr_reset_mode(sk); | |
802 | } | |
803 | } | |
804 | } | |
805 | bbr->idle_restart = 0; | |
806 | } | |
807 | ||
808 | static void bbr_update_model(struct sock *sk, const struct rate_sample *rs) | |
809 | { | |
810 | bbr_update_bw(sk, rs); | |
811 | bbr_update_cycle_phase(sk, rs); | |
812 | bbr_check_full_bw_reached(sk, rs); | |
813 | bbr_check_drain(sk, rs); | |
814 | bbr_update_min_rtt(sk, rs); | |
815 | } | |
816 | ||
817 | static void bbr_main(struct sock *sk, const struct rate_sample *rs) | |
818 | { | |
819 | struct bbr *bbr = inet_csk_ca(sk); | |
820 | u32 bw; | |
821 | ||
822 | bbr_update_model(sk, rs); | |
823 | ||
824 | bw = bbr_bw(sk); | |
825 | bbr_set_pacing_rate(sk, bw, bbr->pacing_gain); | |
826 | bbr_set_tso_segs_goal(sk); | |
827 | bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain); | |
828 | } | |
829 | ||
830 | static void bbr_init(struct sock *sk) | |
831 | { | |
832 | struct tcp_sock *tp = tcp_sk(sk); | |
833 | struct bbr *bbr = inet_csk_ca(sk); | |
0f8782ea NC |
834 | |
835 | bbr->prior_cwnd = 0; | |
836 | bbr->tso_segs_goal = 0; /* default segs per skb until first ACK */ | |
837 | bbr->rtt_cnt = 0; | |
838 | bbr->next_rtt_delivered = 0; | |
839 | bbr->prev_ca_state = TCP_CA_Open; | |
840 | bbr->packet_conservation = 0; | |
841 | ||
842 | bbr->probe_rtt_done_stamp = 0; | |
843 | bbr->probe_rtt_round_done = 0; | |
844 | bbr->min_rtt_us = tcp_min_rtt(tp); | |
2660bfa8 | 845 | bbr->min_rtt_stamp = tcp_jiffies32; |
0f8782ea NC |
846 | |
847 | minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */ | |
848 | ||
32984565 | 849 | bbr->has_seen_rtt = 0; |
79135b89 | 850 | bbr_init_pacing_rate_from_rtt(sk); |
0f8782ea NC |
851 | |
852 | bbr->restore_cwnd = 0; | |
853 | bbr->round_start = 0; | |
854 | bbr->idle_restart = 0; | |
c589e69b | 855 | bbr->full_bw_reached = 0; |
0f8782ea NC |
856 | bbr->full_bw = 0; |
857 | bbr->full_bw_cnt = 0; | |
9a568de4 | 858 | bbr->cycle_mstamp = 0; |
0f8782ea NC |
859 | bbr->cycle_idx = 0; |
860 | bbr_reset_lt_bw_sampling(sk); | |
861 | bbr_reset_startup_mode(sk); | |
218af599 ED |
862 | |
863 | cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED); | |
0f8782ea NC |
864 | } |
865 | ||
866 | static u32 bbr_sndbuf_expand(struct sock *sk) | |
867 | { | |
868 | /* Provision 3 * cwnd since BBR may slow-start even during recovery. */ | |
869 | return 3; | |
870 | } | |
871 | ||
872 | /* In theory BBR does not need to undo the cwnd since it does not | |
873 | * always reduce cwnd on losses (see bbr_main()). Keep it for now. | |
874 | */ | |
875 | static u32 bbr_undo_cwnd(struct sock *sk) | |
876 | { | |
2f6c498e NC |
877 | struct bbr *bbr = inet_csk_ca(sk); |
878 | ||
879 | bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */ | |
880 | bbr->full_bw_cnt = 0; | |
600647d4 | 881 | bbr_reset_lt_bw_sampling(sk); |
0f8782ea NC |
882 | return tcp_sk(sk)->snd_cwnd; |
883 | } | |
884 | ||
885 | /* Entering loss recovery, so save cwnd for when we exit or undo recovery. */ | |
886 | static u32 bbr_ssthresh(struct sock *sk) | |
887 | { | |
888 | bbr_save_cwnd(sk); | |
889 | return TCP_INFINITE_SSTHRESH; /* BBR does not use ssthresh */ | |
890 | } | |
891 | ||
892 | static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr, | |
893 | union tcp_cc_info *info) | |
894 | { | |
895 | if (ext & (1 << (INET_DIAG_BBRINFO - 1)) || | |
896 | ext & (1 << (INET_DIAG_VEGASINFO - 1))) { | |
897 | struct tcp_sock *tp = tcp_sk(sk); | |
898 | struct bbr *bbr = inet_csk_ca(sk); | |
899 | u64 bw = bbr_bw(sk); | |
900 | ||
901 | bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE; | |
902 | memset(&info->bbr, 0, sizeof(info->bbr)); | |
903 | info->bbr.bbr_bw_lo = (u32)bw; | |
904 | info->bbr.bbr_bw_hi = (u32)(bw >> 32); | |
905 | info->bbr.bbr_min_rtt = bbr->min_rtt_us; | |
906 | info->bbr.bbr_pacing_gain = bbr->pacing_gain; | |
907 | info->bbr.bbr_cwnd_gain = bbr->cwnd_gain; | |
908 | *attr = INET_DIAG_BBRINFO; | |
909 | return sizeof(info->bbr); | |
910 | } | |
911 | return 0; | |
912 | } | |
913 | ||
914 | static void bbr_set_state(struct sock *sk, u8 new_state) | |
915 | { | |
916 | struct bbr *bbr = inet_csk_ca(sk); | |
917 | ||
918 | if (new_state == TCP_CA_Loss) { | |
919 | struct rate_sample rs = { .losses = 1 }; | |
920 | ||
921 | bbr->prev_ca_state = TCP_CA_Loss; | |
922 | bbr->full_bw = 0; | |
923 | bbr->round_start = 1; /* treat RTO like end of a round */ | |
924 | bbr_lt_bw_sampling(sk, &rs); | |
925 | } | |
926 | } | |
927 | ||
928 | static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = { | |
929 | .flags = TCP_CONG_NON_RESTRICTED, | |
930 | .name = "bbr", | |
931 | .owner = THIS_MODULE, | |
932 | .init = bbr_init, | |
933 | .cong_control = bbr_main, | |
934 | .sndbuf_expand = bbr_sndbuf_expand, | |
935 | .undo_cwnd = bbr_undo_cwnd, | |
936 | .cwnd_event = bbr_cwnd_event, | |
937 | .ssthresh = bbr_ssthresh, | |
938 | .tso_segs_goal = bbr_tso_segs_goal, | |
939 | .get_info = bbr_get_info, | |
940 | .set_state = bbr_set_state, | |
941 | }; | |
942 | ||
943 | static int __init bbr_register(void) | |
944 | { | |
945 | BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE); | |
946 | return tcp_register_congestion_control(&tcp_bbr_cong_ops); | |
947 | } | |
948 | ||
949 | static void __exit bbr_unregister(void) | |
950 | { | |
951 | tcp_unregister_congestion_control(&tcp_bbr_cong_ops); | |
952 | } | |
953 | ||
954 | module_init(bbr_register); | |
955 | module_exit(bbr_unregister); | |
956 | ||
957 | MODULE_AUTHOR("Van Jacobson <vanj@google.com>"); | |
958 | MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>"); | |
959 | MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>"); | |
960 | MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>"); | |
961 | MODULE_LICENSE("Dual BSD/GPL"); | |
962 | MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)"); |