Commit | Line | Data |
---|---|---|
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? */ | |
0f8782ea | 98 | round_start:1, /* start of packet-timed tx->ack round? */ |
0f8782ea NC |
99 | idle_restart:1, /* restarting after idle? */ |
100 | probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ | |
fb998862 | 101 | unused:13, |
0f8782ea NC |
102 | lt_is_sampling:1, /* taking long-term ("LT") samples now? */ |
103 | lt_rtt_cnt:7, /* round trips in long-term interval */ | |
104 | lt_use_bw:1; /* use lt_bw as our bw estimate? */ | |
105 | u32 lt_bw; /* LT est delivery rate in pkts/uS << 24 */ | |
106 | u32 lt_last_delivered; /* LT intvl start: tp->delivered */ | |
107 | u32 lt_last_stamp; /* LT intvl start: tp->delivered_mstamp */ | |
108 | u32 lt_last_lost; /* LT intvl start: tp->lost */ | |
109 | u32 pacing_gain:10, /* current gain for setting pacing rate */ | |
110 | cwnd_gain:10, /* current gain for setting cwnd */ | |
c589e69b NC |
111 | full_bw_reached:1, /* reached full bw in Startup? */ |
112 | full_bw_cnt:2, /* number of rounds without large bw gains */ | |
0f8782ea | 113 | cycle_idx:3, /* current index in pacing_gain cycle array */ |
32984565 NC |
114 | has_seen_rtt:1, /* have we seen an RTT sample yet? */ |
115 | unused_b:5; | |
0f8782ea NC |
116 | u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ |
117 | u32 full_bw; /* recent bw, to estimate if pipe is full */ | |
118 | }; | |
119 | ||
120 | #define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ | |
121 | ||
122 | /* Window length of bw filter (in rounds): */ | |
123 | static const int bbr_bw_rtts = CYCLE_LEN + 2; | |
124 | /* Window length of min_rtt filter (in sec): */ | |
125 | static const u32 bbr_min_rtt_win_sec = 10; | |
126 | /* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */ | |
127 | static const u32 bbr_probe_rtt_mode_ms = 200; | |
128 | /* Skip TSO below the following bandwidth (bits/sec): */ | |
129 | static const int bbr_min_tso_rate = 1200000; | |
130 | ||
131 | /* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain | |
132 | * that will allow a smoothly increasing pacing rate that will double each RTT | |
133 | * and send the same number of packets per RTT that an un-paced, slow-starting | |
134 | * Reno or CUBIC flow would: | |
135 | */ | |
136 | static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1; | |
137 | /* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain | |
138 | * the queue created in BBR_STARTUP in a single round: | |
139 | */ | |
140 | static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885; | |
141 | /* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */ | |
142 | static const int bbr_cwnd_gain = BBR_UNIT * 2; | |
143 | /* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */ | |
144 | static const int bbr_pacing_gain[] = { | |
145 | BBR_UNIT * 5 / 4, /* probe for more available bw */ | |
146 | BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */ | |
147 | BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */ | |
148 | BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */ | |
149 | }; | |
150 | /* Randomize the starting gain cycling phase over N phases: */ | |
151 | static const u32 bbr_cycle_rand = 7; | |
152 | ||
153 | /* Try to keep at least this many packets in flight, if things go smoothly. For | |
154 | * smooth functioning, a sliding window protocol ACKing every other packet | |
155 | * needs at least 4 packets in flight: | |
156 | */ | |
157 | static const u32 bbr_cwnd_min_target = 4; | |
158 | ||
159 | /* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */ | |
160 | /* If bw has increased significantly (1.25x), there may be more bw available: */ | |
161 | static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4; | |
162 | /* But after 3 rounds w/o significant bw growth, estimate pipe is full: */ | |
163 | static const u32 bbr_full_bw_cnt = 3; | |
164 | ||
165 | /* "long-term" ("LT") bandwidth estimator parameters... */ | |
166 | /* The minimum number of rounds in an LT bw sampling interval: */ | |
167 | static const u32 bbr_lt_intvl_min_rtts = 4; | |
168 | /* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */ | |
169 | static const u32 bbr_lt_loss_thresh = 50; | |
170 | /* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */ | |
171 | static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8; | |
172 | /* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */ | |
173 | static const u32 bbr_lt_bw_diff = 4000 / 8; | |
174 | /* If we estimate we're policed, use lt_bw for this many round trips: */ | |
175 | static const u32 bbr_lt_bw_max_rtts = 48; | |
176 | ||
5490b32d KY |
177 | static void bbr_check_probe_rtt_done(struct sock *sk); |
178 | ||
0f8782ea NC |
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 | { | |
cadefe5f ED |
209 | unsigned int mss = tcp_sk(sk)->mss_cache; |
210 | ||
211 | if (!tcp_needs_internal_pacing(sk)) | |
212 | mss = tcp_mss_to_mtu(sk, mss); | |
213 | rate *= mss; | |
0f8782ea NC |
214 | rate *= gain; |
215 | rate >>= BBR_SCALE; | |
216 | rate *= USEC_PER_SEC; | |
217 | return rate >> BW_SCALE; | |
218 | } | |
219 | ||
f19fd62d NC |
220 | /* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */ |
221 | static u32 bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain) | |
222 | { | |
223 | u64 rate = bw; | |
224 | ||
225 | rate = bbr_rate_bytes_per_sec(sk, rate, gain); | |
226 | rate = min_t(u64, rate, sk->sk_max_pacing_rate); | |
227 | return rate; | |
228 | } | |
229 | ||
79135b89 NC |
230 | /* Initialize pacing rate to: high_gain * init_cwnd / RTT. */ |
231 | static void bbr_init_pacing_rate_from_rtt(struct sock *sk) | |
232 | { | |
233 | struct tcp_sock *tp = tcp_sk(sk); | |
32984565 | 234 | struct bbr *bbr = inet_csk_ca(sk); |
79135b89 NC |
235 | u64 bw; |
236 | u32 rtt_us; | |
237 | ||
238 | if (tp->srtt_us) { /* any RTT sample yet? */ | |
239 | rtt_us = max(tp->srtt_us >> 3, 1U); | |
32984565 | 240 | bbr->has_seen_rtt = 1; |
79135b89 NC |
241 | } else { /* no RTT sample yet */ |
242 | rtt_us = USEC_PER_MSEC; /* use nominal default RTT */ | |
243 | } | |
244 | bw = (u64)tp->snd_cwnd * BW_UNIT; | |
245 | do_div(bw, rtt_us); | |
246 | sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain); | |
247 | } | |
248 | ||
0f8782ea NC |
249 | /* Pace using current bw estimate and a gain factor. In order to help drive the |
250 | * network toward lower queues while maintaining high utilization and low | |
251 | * latency, the average pacing rate aims to be slightly (~1%) lower than the | |
252 | * estimated bandwidth. This is an important aspect of the design. In this | |
253 | * implementation this slightly lower pacing rate is achieved implicitly by not | |
254 | * including link-layer headers in the packet size used for the pacing rate. | |
255 | */ | |
256 | static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) | |
257 | { | |
32984565 NC |
258 | struct tcp_sock *tp = tcp_sk(sk); |
259 | struct bbr *bbr = inet_csk_ca(sk); | |
f19fd62d | 260 | u32 rate = bbr_bw_to_pacing_rate(sk, bw, gain); |
0f8782ea | 261 | |
32984565 NC |
262 | if (unlikely(!bbr->has_seen_rtt && tp->srtt_us)) |
263 | bbr_init_pacing_rate_from_rtt(sk); | |
4aea287e | 264 | if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate) |
0f8782ea NC |
265 | sk->sk_pacing_rate = rate; |
266 | } | |
267 | ||
dcb8c9b4 ED |
268 | /* override sysctl_tcp_min_tso_segs */ |
269 | static u32 bbr_min_tso_segs(struct sock *sk) | |
0f8782ea | 270 | { |
dcb8c9b4 | 271 | return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2; |
0f8782ea NC |
272 | } |
273 | ||
71abf467 | 274 | static u32 bbr_tso_segs_goal(struct sock *sk) |
0f8782ea NC |
275 | { |
276 | struct tcp_sock *tp = tcp_sk(sk); | |
dcb8c9b4 ED |
277 | u32 segs, bytes; |
278 | ||
279 | /* Sort of tcp_tso_autosize() but ignoring | |
280 | * driver provided sk_gso_max_size. | |
281 | */ | |
282 | bytes = min_t(u32, sk->sk_pacing_rate >> sk->sk_pacing_shift, | |
283 | GSO_MAX_SIZE - 1 - MAX_TCP_HEADER); | |
284 | segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk)); | |
0f8782ea | 285 | |
71abf467 | 286 | return min(segs, 0x7FU); |
0f8782ea NC |
287 | } |
288 | ||
289 | /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */ | |
290 | static void bbr_save_cwnd(struct sock *sk) | |
291 | { | |
292 | struct tcp_sock *tp = tcp_sk(sk); | |
293 | struct bbr *bbr = inet_csk_ca(sk); | |
294 | ||
295 | if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT) | |
296 | bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */ | |
297 | else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */ | |
298 | bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd); | |
299 | } | |
300 | ||
301 | static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) | |
302 | { | |
303 | struct tcp_sock *tp = tcp_sk(sk); | |
304 | struct bbr *bbr = inet_csk_ca(sk); | |
305 | ||
306 | if (event == CA_EVENT_TX_START && tp->app_limited) { | |
307 | bbr->idle_restart = 1; | |
308 | /* Avoid pointless buffer overflows: pace at est. bw if we don't | |
309 | * need more speed (we're restarting from idle and app-limited). | |
310 | */ | |
311 | if (bbr->mode == BBR_PROBE_BW) | |
312 | bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); | |
5490b32d KY |
313 | else if (bbr->mode == BBR_PROBE_RTT) |
314 | bbr_check_probe_rtt_done(sk); | |
0f8782ea NC |
315 | } |
316 | } | |
317 | ||
318 | /* Find target cwnd. Right-size the cwnd based on min RTT and the | |
319 | * estimated bottleneck bandwidth: | |
320 | * | |
321 | * cwnd = bw * min_rtt * gain = BDP * gain | |
322 | * | |
323 | * The key factor, gain, controls the amount of queue. While a small gain | |
324 | * builds a smaller queue, it becomes more vulnerable to noise in RTT | |
325 | * measurements (e.g., delayed ACKs or other ACK compression effects). This | |
326 | * noise may cause BBR to under-estimate the rate. | |
327 | * | |
328 | * To achieve full performance in high-speed paths, we budget enough cwnd to | |
329 | * fit full-sized skbs in-flight on both end hosts to fully utilize the path: | |
330 | * - one skb in sending host Qdisc, | |
331 | * - one skb in sending host TSO/GSO engine | |
332 | * - one skb being received by receiver host LRO/GRO/delayed-ACK engine | |
333 | * Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because | |
334 | * in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets, | |
335 | * which allows 2 outstanding 2-packet sequences, to try to keep pipe | |
336 | * full even with ACK-every-other-packet delayed ACKs. | |
337 | */ | |
338 | static u32 bbr_target_cwnd(struct sock *sk, u32 bw, int gain) | |
339 | { | |
340 | struct bbr *bbr = inet_csk_ca(sk); | |
341 | u32 cwnd; | |
342 | u64 w; | |
343 | ||
344 | /* If we've never had a valid RTT sample, cap cwnd at the initial | |
345 | * default. This should only happen when the connection is not using TCP | |
346 | * timestamps and has retransmitted all of the SYN/SYNACK/data packets | |
347 | * ACKed so far. In this case, an RTO can cut cwnd to 1, in which | |
348 | * case we need to slow-start up toward something safe: TCP_INIT_CWND. | |
349 | */ | |
350 | if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */ | |
351 | return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/ | |
352 | ||
353 | w = (u64)bw * bbr->min_rtt_us; | |
354 | ||
355 | /* Apply a gain to the given value, then remove the BW_SCALE shift. */ | |
356 | cwnd = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; | |
357 | ||
358 | /* Allow enough full-sized skbs in flight to utilize end systems. */ | |
71abf467 | 359 | cwnd += 3 * bbr_tso_segs_goal(sk); |
0f8782ea NC |
360 | |
361 | /* Reduce delayed ACKs by rounding up cwnd to the next even number. */ | |
362 | cwnd = (cwnd + 1) & ~1U; | |
363 | ||
383d4709 NC |
364 | /* Ensure gain cycling gets inflight above BDP even for small BDPs. */ |
365 | if (bbr->mode == BBR_PROBE_BW && gain > BBR_UNIT) | |
366 | cwnd += 2; | |
367 | ||
0f8782ea NC |
368 | return cwnd; |
369 | } | |
370 | ||
371 | /* An optimization in BBR to reduce losses: On the first round of recovery, we | |
372 | * follow the packet conservation principle: send P packets per P packets acked. | |
373 | * After that, we slow-start and send at most 2*P packets per P packets acked. | |
374 | * After recovery finishes, or upon undo, we restore the cwnd we had when | |
375 | * recovery started (capped by the target cwnd based on estimated BDP). | |
376 | * | |
377 | * TODO(ycheng/ncardwell): implement a rate-based approach. | |
378 | */ | |
379 | static bool bbr_set_cwnd_to_recover_or_restore( | |
380 | struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd) | |
381 | { | |
382 | struct tcp_sock *tp = tcp_sk(sk); | |
383 | struct bbr *bbr = inet_csk_ca(sk); | |
384 | u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state; | |
385 | u32 cwnd = tp->snd_cwnd; | |
386 | ||
387 | /* An ACK for P pkts should release at most 2*P packets. We do this | |
388 | * in two steps. First, here we deduct the number of lost packets. | |
389 | * Then, in bbr_set_cwnd() we slow start up toward the target cwnd. | |
390 | */ | |
391 | if (rs->losses > 0) | |
392 | cwnd = max_t(s32, cwnd - rs->losses, 1); | |
393 | ||
394 | if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) { | |
395 | /* Starting 1st round of Recovery, so do packet conservation. */ | |
396 | bbr->packet_conservation = 1; | |
397 | bbr->next_rtt_delivered = tp->delivered; /* start round now */ | |
398 | /* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */ | |
399 | cwnd = tcp_packets_in_flight(tp) + acked; | |
400 | } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) { | |
401 | /* Exiting loss recovery; restore cwnd saved before recovery. */ | |
fb998862 | 402 | cwnd = max(cwnd, bbr->prior_cwnd); |
0f8782ea NC |
403 | bbr->packet_conservation = 0; |
404 | } | |
405 | bbr->prev_ca_state = state; | |
406 | ||
0f8782ea NC |
407 | if (bbr->packet_conservation) { |
408 | *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked); | |
409 | return true; /* yes, using packet conservation */ | |
410 | } | |
411 | *new_cwnd = cwnd; | |
412 | return false; | |
413 | } | |
414 | ||
415 | /* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss | |
416 | * has drawn us down below target), or snap down to target if we're above it. | |
417 | */ | |
418 | static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, | |
419 | u32 acked, u32 bw, int gain) | |
420 | { | |
421 | struct tcp_sock *tp = tcp_sk(sk); | |
422 | struct bbr *bbr = inet_csk_ca(sk); | |
8e995bf1 | 423 | u32 cwnd = tp->snd_cwnd, target_cwnd = 0; |
0f8782ea NC |
424 | |
425 | if (!acked) | |
8e995bf1 | 426 | goto done; /* no packet fully ACKed; just apply caps */ |
0f8782ea NC |
427 | |
428 | if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) | |
429 | goto done; | |
430 | ||
431 | /* If we're below target cwnd, slow start cwnd toward target cwnd. */ | |
432 | target_cwnd = bbr_target_cwnd(sk, bw, gain); | |
433 | if (bbr_full_bw_reached(sk)) /* only cut cwnd if we filled the pipe */ | |
434 | cwnd = min(cwnd + acked, target_cwnd); | |
435 | else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND) | |
436 | cwnd = cwnd + acked; | |
437 | cwnd = max(cwnd, bbr_cwnd_min_target); | |
438 | ||
439 | done: | |
440 | tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); /* apply global cap */ | |
441 | if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */ | |
442 | tp->snd_cwnd = min(tp->snd_cwnd, bbr_cwnd_min_target); | |
443 | } | |
444 | ||
445 | /* End cycle phase if it's time and/or we hit the phase's in-flight target. */ | |
446 | static bool bbr_is_next_cycle_phase(struct sock *sk, | |
447 | const struct rate_sample *rs) | |
448 | { | |
449 | struct tcp_sock *tp = tcp_sk(sk); | |
450 | struct bbr *bbr = inet_csk_ca(sk); | |
451 | bool is_full_length = | |
9a568de4 | 452 | tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp) > |
0f8782ea NC |
453 | bbr->min_rtt_us; |
454 | u32 inflight, bw; | |
455 | ||
456 | /* The pacing_gain of 1.0 paces at the estimated bw to try to fully | |
457 | * use the pipe without increasing the queue. | |
458 | */ | |
459 | if (bbr->pacing_gain == BBR_UNIT) | |
460 | return is_full_length; /* just use wall clock time */ | |
461 | ||
462 | inflight = rs->prior_in_flight; /* what was in-flight before ACK? */ | |
463 | bw = bbr_max_bw(sk); | |
464 | ||
465 | /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at | |
466 | * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is | |
467 | * small (e.g. on a LAN). We do not persist if packets are lost, since | |
468 | * a path with small buffers may not hold that much. | |
469 | */ | |
470 | if (bbr->pacing_gain > BBR_UNIT) | |
471 | return is_full_length && | |
472 | (rs->losses || /* perhaps pacing_gain*BDP won't fit */ | |
473 | inflight >= bbr_target_cwnd(sk, bw, bbr->pacing_gain)); | |
474 | ||
475 | /* A pacing_gain < 1.0 tries to drain extra queue we added if bw | |
476 | * probing didn't find more bw. If inflight falls to match BDP then we | |
477 | * estimate queue is drained; persisting would underutilize the pipe. | |
478 | */ | |
479 | return is_full_length || | |
480 | inflight <= bbr_target_cwnd(sk, bw, BBR_UNIT); | |
481 | } | |
482 | ||
483 | static void bbr_advance_cycle_phase(struct sock *sk) | |
484 | { | |
485 | struct tcp_sock *tp = tcp_sk(sk); | |
486 | struct bbr *bbr = inet_csk_ca(sk); | |
487 | ||
488 | bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1); | |
489 | bbr->cycle_mstamp = tp->delivered_mstamp; | |
3aff3b4b NC |
490 | bbr->pacing_gain = bbr->lt_use_bw ? BBR_UNIT : |
491 | bbr_pacing_gain[bbr->cycle_idx]; | |
0f8782ea NC |
492 | } |
493 | ||
494 | /* Gain cycling: cycle pacing gain to converge to fair share of available bw. */ | |
495 | static void bbr_update_cycle_phase(struct sock *sk, | |
496 | const struct rate_sample *rs) | |
497 | { | |
498 | struct bbr *bbr = inet_csk_ca(sk); | |
499 | ||
3aff3b4b | 500 | if (bbr->mode == BBR_PROBE_BW && bbr_is_next_cycle_phase(sk, rs)) |
0f8782ea NC |
501 | bbr_advance_cycle_phase(sk); |
502 | } | |
503 | ||
504 | static void bbr_reset_startup_mode(struct sock *sk) | |
505 | { | |
506 | struct bbr *bbr = inet_csk_ca(sk); | |
507 | ||
508 | bbr->mode = BBR_STARTUP; | |
509 | bbr->pacing_gain = bbr_high_gain; | |
510 | bbr->cwnd_gain = bbr_high_gain; | |
511 | } | |
512 | ||
513 | static void bbr_reset_probe_bw_mode(struct sock *sk) | |
514 | { | |
515 | struct bbr *bbr = inet_csk_ca(sk); | |
516 | ||
517 | bbr->mode = BBR_PROBE_BW; | |
518 | bbr->pacing_gain = BBR_UNIT; | |
519 | bbr->cwnd_gain = bbr_cwnd_gain; | |
520 | bbr->cycle_idx = CYCLE_LEN - 1 - prandom_u32_max(bbr_cycle_rand); | |
521 | bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */ | |
522 | } | |
523 | ||
524 | static void bbr_reset_mode(struct sock *sk) | |
525 | { | |
526 | if (!bbr_full_bw_reached(sk)) | |
527 | bbr_reset_startup_mode(sk); | |
528 | else | |
529 | bbr_reset_probe_bw_mode(sk); | |
530 | } | |
531 | ||
532 | /* Start a new long-term sampling interval. */ | |
533 | static void bbr_reset_lt_bw_sampling_interval(struct sock *sk) | |
534 | { | |
535 | struct tcp_sock *tp = tcp_sk(sk); | |
536 | struct bbr *bbr = inet_csk_ca(sk); | |
537 | ||
9a568de4 | 538 | bbr->lt_last_stamp = div_u64(tp->delivered_mstamp, USEC_PER_MSEC); |
0f8782ea NC |
539 | bbr->lt_last_delivered = tp->delivered; |
540 | bbr->lt_last_lost = tp->lost; | |
541 | bbr->lt_rtt_cnt = 0; | |
542 | } | |
543 | ||
544 | /* Completely reset long-term bandwidth sampling. */ | |
545 | static void bbr_reset_lt_bw_sampling(struct sock *sk) | |
546 | { | |
547 | struct bbr *bbr = inet_csk_ca(sk); | |
548 | ||
549 | bbr->lt_bw = 0; | |
550 | bbr->lt_use_bw = 0; | |
551 | bbr->lt_is_sampling = false; | |
552 | bbr_reset_lt_bw_sampling_interval(sk); | |
553 | } | |
554 | ||
555 | /* Long-term bw sampling interval is done. Estimate whether we're policed. */ | |
556 | static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw) | |
557 | { | |
558 | struct bbr *bbr = inet_csk_ca(sk); | |
559 | u32 diff; | |
560 | ||
561 | if (bbr->lt_bw) { /* do we have bw from a previous interval? */ | |
562 | /* Is new bw close to the lt_bw from the previous interval? */ | |
563 | diff = abs(bw - bbr->lt_bw); | |
564 | if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) || | |
565 | (bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <= | |
566 | bbr_lt_bw_diff)) { | |
567 | /* All criteria are met; estimate we're policed. */ | |
568 | bbr->lt_bw = (bw + bbr->lt_bw) >> 1; /* avg 2 intvls */ | |
569 | bbr->lt_use_bw = 1; | |
570 | bbr->pacing_gain = BBR_UNIT; /* try to avoid drops */ | |
571 | bbr->lt_rtt_cnt = 0; | |
572 | return; | |
573 | } | |
574 | } | |
575 | bbr->lt_bw = bw; | |
576 | bbr_reset_lt_bw_sampling_interval(sk); | |
577 | } | |
578 | ||
579 | /* Token-bucket traffic policers are common (see "An Internet-Wide Analysis of | |
580 | * Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers and | |
581 | * explicitly models their policed rate, to reduce unnecessary losses. We | |
582 | * estimate that we're policed if we see 2 consecutive sampling intervals with | |
583 | * consistent throughput and high packet loss. If we think we're being policed, | |
584 | * set lt_bw to the "long-term" average delivery rate from those 2 intervals. | |
585 | */ | |
586 | static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs) | |
587 | { | |
588 | struct tcp_sock *tp = tcp_sk(sk); | |
589 | struct bbr *bbr = inet_csk_ca(sk); | |
590 | u32 lost, delivered; | |
591 | u64 bw; | |
9a568de4 | 592 | u32 t; |
0f8782ea NC |
593 | |
594 | if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */ | |
595 | if (bbr->mode == BBR_PROBE_BW && bbr->round_start && | |
596 | ++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) { | |
597 | bbr_reset_lt_bw_sampling(sk); /* stop using lt_bw */ | |
598 | bbr_reset_probe_bw_mode(sk); /* restart gain cycling */ | |
599 | } | |
600 | return; | |
601 | } | |
602 | ||
603 | /* Wait for the first loss before sampling, to let the policer exhaust | |
604 | * its tokens and estimate the steady-state rate allowed by the policer. | |
605 | * Starting samples earlier includes bursts that over-estimate the bw. | |
606 | */ | |
607 | if (!bbr->lt_is_sampling) { | |
608 | if (!rs->losses) | |
609 | return; | |
610 | bbr_reset_lt_bw_sampling_interval(sk); | |
611 | bbr->lt_is_sampling = true; | |
612 | } | |
613 | ||
614 | /* To avoid underestimates, reset sampling if we run out of data. */ | |
615 | if (rs->is_app_limited) { | |
616 | bbr_reset_lt_bw_sampling(sk); | |
617 | return; | |
618 | } | |
619 | ||
620 | if (bbr->round_start) | |
621 | bbr->lt_rtt_cnt++; /* count round trips in this interval */ | |
622 | if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts) | |
623 | return; /* sampling interval needs to be longer */ | |
624 | if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) { | |
625 | bbr_reset_lt_bw_sampling(sk); /* interval is too long */ | |
626 | return; | |
627 | } | |
628 | ||
629 | /* End sampling interval when a packet is lost, so we estimate the | |
630 | * policer tokens were exhausted. Stopping the sampling before the | |
631 | * tokens are exhausted under-estimates the policed rate. | |
632 | */ | |
633 | if (!rs->losses) | |
634 | return; | |
635 | ||
636 | /* Calculate packets lost and delivered in sampling interval. */ | |
637 | lost = tp->lost - bbr->lt_last_lost; | |
638 | delivered = tp->delivered - bbr->lt_last_delivered; | |
639 | /* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */ | |
640 | if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered) | |
641 | return; | |
642 | ||
643 | /* Find average delivery rate in this sampling interval. */ | |
9a568de4 ED |
644 | t = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp; |
645 | if ((s32)t < 1) | |
646 | return; /* interval is less than one ms, so wait */ | |
647 | /* Check if can multiply without overflow */ | |
648 | if (t >= ~0U / USEC_PER_MSEC) { | |
0f8782ea NC |
649 | bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */ |
650 | return; | |
651 | } | |
9a568de4 | 652 | t *= USEC_PER_MSEC; |
0f8782ea NC |
653 | bw = (u64)delivered * BW_UNIT; |
654 | do_div(bw, t); | |
655 | bbr_lt_bw_interval_done(sk, bw); | |
656 | } | |
657 | ||
658 | /* Estimate the bandwidth based on how fast packets are delivered */ | |
659 | static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs) | |
660 | { | |
661 | struct tcp_sock *tp = tcp_sk(sk); | |
662 | struct bbr *bbr = inet_csk_ca(sk); | |
663 | u64 bw; | |
664 | ||
665 | bbr->round_start = 0; | |
666 | if (rs->delivered < 0 || rs->interval_us <= 0) | |
667 | return; /* Not a valid observation */ | |
668 | ||
669 | /* See if we've reached the next RTT */ | |
670 | if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) { | |
671 | bbr->next_rtt_delivered = tp->delivered; | |
672 | bbr->rtt_cnt++; | |
673 | bbr->round_start = 1; | |
674 | bbr->packet_conservation = 0; | |
675 | } | |
676 | ||
677 | bbr_lt_bw_sampling(sk, rs); | |
678 | ||
679 | /* Divide delivered by the interval to find a (lower bound) bottleneck | |
680 | * bandwidth sample. Delivered is in packets and interval_us in uS and | |
681 | * ratio will be <<1 for most connections. So delivered is first scaled. | |
682 | */ | |
683 | bw = (u64)rs->delivered * BW_UNIT; | |
684 | do_div(bw, rs->interval_us); | |
685 | ||
686 | /* If this sample is application-limited, it is likely to have a very | |
687 | * low delivered count that represents application behavior rather than | |
688 | * the available network rate. Such a sample could drag down estimated | |
689 | * bw, causing needless slow-down. Thus, to continue to send at the | |
690 | * last measured network rate, we filter out app-limited samples unless | |
691 | * they describe the path bw at least as well as our bw model. | |
692 | * | |
693 | * So the goal during app-limited phase is to proceed with the best | |
694 | * network rate no matter how long. We automatically leave this | |
695 | * phase when app writes faster than the network can deliver :) | |
696 | */ | |
697 | if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) { | |
698 | /* Incorporate new sample into our max bw filter. */ | |
699 | minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw); | |
700 | } | |
701 | } | |
702 | ||
703 | /* Estimate when the pipe is full, using the change in delivery rate: BBR | |
704 | * estimates that STARTUP filled the pipe if the estimated bw hasn't changed by | |
705 | * at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited | |
706 | * rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the | |
707 | * higher rwin, 3: we get higher delivery rate samples. Or transient | |
708 | * cross-traffic or radio noise can go away. CUBIC Hystart shares a similar | |
709 | * design goal, but uses delay and inter-ACK spacing instead of bandwidth. | |
710 | */ | |
711 | static void bbr_check_full_bw_reached(struct sock *sk, | |
712 | const struct rate_sample *rs) | |
713 | { | |
714 | struct bbr *bbr = inet_csk_ca(sk); | |
715 | u32 bw_thresh; | |
716 | ||
717 | if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited) | |
718 | return; | |
719 | ||
720 | bw_thresh = (u64)bbr->full_bw * bbr_full_bw_thresh >> BBR_SCALE; | |
721 | if (bbr_max_bw(sk) >= bw_thresh) { | |
722 | bbr->full_bw = bbr_max_bw(sk); | |
723 | bbr->full_bw_cnt = 0; | |
724 | return; | |
725 | } | |
726 | ++bbr->full_bw_cnt; | |
c589e69b | 727 | bbr->full_bw_reached = bbr->full_bw_cnt >= bbr_full_bw_cnt; |
0f8782ea NC |
728 | } |
729 | ||
730 | /* If pipe is probably full, drain the queue and then enter steady-state. */ | |
731 | static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs) | |
732 | { | |
733 | struct bbr *bbr = inet_csk_ca(sk); | |
734 | ||
735 | if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) { | |
736 | bbr->mode = BBR_DRAIN; /* drain queue we created */ | |
737 | bbr->pacing_gain = bbr_drain_gain; /* pace slow to drain */ | |
738 | bbr->cwnd_gain = bbr_high_gain; /* maintain cwnd */ | |
53794570 YS |
739 | tcp_sk(sk)->snd_ssthresh = |
740 | bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT); | |
0f8782ea NC |
741 | } /* fall through to check if in-flight is already small: */ |
742 | if (bbr->mode == BBR_DRAIN && | |
743 | tcp_packets_in_flight(tcp_sk(sk)) <= | |
744 | bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT)) | |
745 | bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ | |
746 | } | |
747 | ||
fb998862 KY |
748 | static void bbr_check_probe_rtt_done(struct sock *sk) |
749 | { | |
750 | struct tcp_sock *tp = tcp_sk(sk); | |
751 | struct bbr *bbr = inet_csk_ca(sk); | |
752 | ||
753 | if (!(bbr->probe_rtt_done_stamp && | |
754 | after(tcp_jiffies32, bbr->probe_rtt_done_stamp))) | |
755 | return; | |
756 | ||
757 | bbr->min_rtt_stamp = tcp_jiffies32; /* wait a while until PROBE_RTT */ | |
758 | tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd); | |
759 | bbr_reset_mode(sk); | |
760 | } | |
761 | ||
0f8782ea NC |
762 | /* The goal of PROBE_RTT mode is to have BBR flows cooperatively and |
763 | * periodically drain the bottleneck queue, to converge to measure the true | |
764 | * min_rtt (unloaded propagation delay). This allows the flows to keep queues | |
765 | * small (reducing queuing delay and packet loss) and achieve fairness among | |
766 | * BBR flows. | |
767 | * | |
768 | * The min_rtt filter window is 10 seconds. When the min_rtt estimate expires, | |
769 | * we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets. | |
770 | * After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed | |
771 | * round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and | |
772 | * re-enter the previous mode. BBR uses 200ms to approximately bound the | |
773 | * performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s). | |
774 | * | |
775 | * Note that flows need only pay 2% if they are busy sending over the last 10 | |
776 | * seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have | |
777 | * natural silences or low-rate periods within 10 seconds where the rate is low | |
778 | * enough for long enough to drain its queue in the bottleneck. We pick up | |
779 | * these min RTT measurements opportunistically with our min_rtt filter. :-) | |
780 | */ | |
781 | static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) | |
782 | { | |
783 | struct tcp_sock *tp = tcp_sk(sk); | |
784 | struct bbr *bbr = inet_csk_ca(sk); | |
785 | bool filter_expired; | |
786 | ||
787 | /* Track min RTT seen in the min_rtt_win_sec filter window: */ | |
2660bfa8 | 788 | filter_expired = after(tcp_jiffies32, |
0f8782ea NC |
789 | bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); |
790 | if (rs->rtt_us >= 0 && | |
e4286603 YC |
791 | (rs->rtt_us <= bbr->min_rtt_us || |
792 | (filter_expired && !rs->is_ack_delayed))) { | |
0f8782ea | 793 | bbr->min_rtt_us = rs->rtt_us; |
2660bfa8 | 794 | bbr->min_rtt_stamp = tcp_jiffies32; |
0f8782ea NC |
795 | } |
796 | ||
797 | if (bbr_probe_rtt_mode_ms > 0 && filter_expired && | |
798 | !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) { | |
799 | bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */ | |
800 | bbr->pacing_gain = BBR_UNIT; | |
801 | bbr->cwnd_gain = BBR_UNIT; | |
802 | bbr_save_cwnd(sk); /* note cwnd so we can restore it */ | |
803 | bbr->probe_rtt_done_stamp = 0; | |
804 | } | |
805 | ||
806 | if (bbr->mode == BBR_PROBE_RTT) { | |
807 | /* Ignore low rate samples during this mode. */ | |
808 | tp->app_limited = | |
809 | (tp->delivered + tcp_packets_in_flight(tp)) ? : 1; | |
810 | /* Maintain min packets in flight for max(200 ms, 1 round). */ | |
811 | if (!bbr->probe_rtt_done_stamp && | |
812 | tcp_packets_in_flight(tp) <= bbr_cwnd_min_target) { | |
2660bfa8 | 813 | bbr->probe_rtt_done_stamp = tcp_jiffies32 + |
0f8782ea NC |
814 | msecs_to_jiffies(bbr_probe_rtt_mode_ms); |
815 | bbr->probe_rtt_round_done = 0; | |
816 | bbr->next_rtt_delivered = tp->delivered; | |
817 | } else if (bbr->probe_rtt_done_stamp) { | |
818 | if (bbr->round_start) | |
819 | bbr->probe_rtt_round_done = 1; | |
fb998862 KY |
820 | if (bbr->probe_rtt_round_done) |
821 | bbr_check_probe_rtt_done(sk); | |
0f8782ea NC |
822 | } |
823 | } | |
e6e6a278 NC |
824 | /* Restart after idle ends only once we process a new S/ACK for data */ |
825 | if (rs->delivered > 0) | |
826 | bbr->idle_restart = 0; | |
0f8782ea NC |
827 | } |
828 | ||
829 | static void bbr_update_model(struct sock *sk, const struct rate_sample *rs) | |
830 | { | |
831 | bbr_update_bw(sk, rs); | |
832 | bbr_update_cycle_phase(sk, rs); | |
833 | bbr_check_full_bw_reached(sk, rs); | |
834 | bbr_check_drain(sk, rs); | |
835 | bbr_update_min_rtt(sk, rs); | |
836 | } | |
837 | ||
838 | static void bbr_main(struct sock *sk, const struct rate_sample *rs) | |
839 | { | |
840 | struct bbr *bbr = inet_csk_ca(sk); | |
841 | u32 bw; | |
842 | ||
843 | bbr_update_model(sk, rs); | |
844 | ||
845 | bw = bbr_bw(sk); | |
846 | bbr_set_pacing_rate(sk, bw, bbr->pacing_gain); | |
0f8782ea NC |
847 | bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain); |
848 | } | |
849 | ||
850 | static void bbr_init(struct sock *sk) | |
851 | { | |
852 | struct tcp_sock *tp = tcp_sk(sk); | |
853 | struct bbr *bbr = inet_csk_ca(sk); | |
0f8782ea NC |
854 | |
855 | bbr->prior_cwnd = 0; | |
53794570 | 856 | tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; |
0f8782ea NC |
857 | bbr->rtt_cnt = 0; |
858 | bbr->next_rtt_delivered = 0; | |
859 | bbr->prev_ca_state = TCP_CA_Open; | |
860 | bbr->packet_conservation = 0; | |
861 | ||
862 | bbr->probe_rtt_done_stamp = 0; | |
863 | bbr->probe_rtt_round_done = 0; | |
864 | bbr->min_rtt_us = tcp_min_rtt(tp); | |
2660bfa8 | 865 | bbr->min_rtt_stamp = tcp_jiffies32; |
0f8782ea NC |
866 | |
867 | minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */ | |
868 | ||
32984565 | 869 | bbr->has_seen_rtt = 0; |
79135b89 | 870 | bbr_init_pacing_rate_from_rtt(sk); |
0f8782ea | 871 | |
0f8782ea NC |
872 | bbr->round_start = 0; |
873 | bbr->idle_restart = 0; | |
c589e69b | 874 | bbr->full_bw_reached = 0; |
0f8782ea NC |
875 | bbr->full_bw = 0; |
876 | bbr->full_bw_cnt = 0; | |
9a568de4 | 877 | bbr->cycle_mstamp = 0; |
0f8782ea NC |
878 | bbr->cycle_idx = 0; |
879 | bbr_reset_lt_bw_sampling(sk); | |
880 | bbr_reset_startup_mode(sk); | |
218af599 ED |
881 | |
882 | cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED); | |
0f8782ea NC |
883 | } |
884 | ||
885 | static u32 bbr_sndbuf_expand(struct sock *sk) | |
886 | { | |
887 | /* Provision 3 * cwnd since BBR may slow-start even during recovery. */ | |
888 | return 3; | |
889 | } | |
890 | ||
891 | /* In theory BBR does not need to undo the cwnd since it does not | |
892 | * always reduce cwnd on losses (see bbr_main()). Keep it for now. | |
893 | */ | |
894 | static u32 bbr_undo_cwnd(struct sock *sk) | |
895 | { | |
2f6c498e NC |
896 | struct bbr *bbr = inet_csk_ca(sk); |
897 | ||
898 | bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */ | |
899 | bbr->full_bw_cnt = 0; | |
600647d4 | 900 | bbr_reset_lt_bw_sampling(sk); |
0f8782ea NC |
901 | return tcp_sk(sk)->snd_cwnd; |
902 | } | |
903 | ||
904 | /* Entering loss recovery, so save cwnd for when we exit or undo recovery. */ | |
905 | static u32 bbr_ssthresh(struct sock *sk) | |
906 | { | |
907 | bbr_save_cwnd(sk); | |
53794570 | 908 | return tcp_sk(sk)->snd_ssthresh; |
0f8782ea NC |
909 | } |
910 | ||
911 | static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr, | |
912 | union tcp_cc_info *info) | |
913 | { | |
914 | if (ext & (1 << (INET_DIAG_BBRINFO - 1)) || | |
915 | ext & (1 << (INET_DIAG_VEGASINFO - 1))) { | |
916 | struct tcp_sock *tp = tcp_sk(sk); | |
917 | struct bbr *bbr = inet_csk_ca(sk); | |
918 | u64 bw = bbr_bw(sk); | |
919 | ||
920 | bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE; | |
921 | memset(&info->bbr, 0, sizeof(info->bbr)); | |
922 | info->bbr.bbr_bw_lo = (u32)bw; | |
923 | info->bbr.bbr_bw_hi = (u32)(bw >> 32); | |
924 | info->bbr.bbr_min_rtt = bbr->min_rtt_us; | |
925 | info->bbr.bbr_pacing_gain = bbr->pacing_gain; | |
926 | info->bbr.bbr_cwnd_gain = bbr->cwnd_gain; | |
927 | *attr = INET_DIAG_BBRINFO; | |
928 | return sizeof(info->bbr); | |
929 | } | |
930 | return 0; | |
931 | } | |
932 | ||
933 | static void bbr_set_state(struct sock *sk, u8 new_state) | |
934 | { | |
935 | struct bbr *bbr = inet_csk_ca(sk); | |
936 | ||
937 | if (new_state == TCP_CA_Loss) { | |
938 | struct rate_sample rs = { .losses = 1 }; | |
939 | ||
940 | bbr->prev_ca_state = TCP_CA_Loss; | |
941 | bbr->full_bw = 0; | |
942 | bbr->round_start = 1; /* treat RTO like end of a round */ | |
943 | bbr_lt_bw_sampling(sk, &rs); | |
944 | } | |
945 | } | |
946 | ||
947 | static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = { | |
948 | .flags = TCP_CONG_NON_RESTRICTED, | |
949 | .name = "bbr", | |
950 | .owner = THIS_MODULE, | |
951 | .init = bbr_init, | |
952 | .cong_control = bbr_main, | |
953 | .sndbuf_expand = bbr_sndbuf_expand, | |
954 | .undo_cwnd = bbr_undo_cwnd, | |
955 | .cwnd_event = bbr_cwnd_event, | |
956 | .ssthresh = bbr_ssthresh, | |
dcb8c9b4 | 957 | .min_tso_segs = bbr_min_tso_segs, |
0f8782ea NC |
958 | .get_info = bbr_get_info, |
959 | .set_state = bbr_set_state, | |
960 | }; | |
961 | ||
962 | static int __init bbr_register(void) | |
963 | { | |
964 | BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE); | |
965 | return tcp_register_congestion_control(&tcp_bbr_cong_ops); | |
966 | } | |
967 | ||
968 | static void __exit bbr_unregister(void) | |
969 | { | |
970 | tcp_unregister_congestion_control(&tcp_bbr_cong_ops); | |
971 | } | |
972 | ||
973 | module_init(bbr_register); | |
974 | module_exit(bbr_unregister); | |
975 | ||
976 | MODULE_AUTHOR("Van Jacobson <vanj@google.com>"); | |
977 | MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>"); | |
978 | MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>"); | |
979 | MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>"); | |
980 | MODULE_LICENSE("Dual BSD/GPL"); | |
981 | MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)"); |