1 // SPDX-License-Identifier: GPL-2.0-only
2
3 /* WARNING: This implementation is not necessarily the same
4 * as the tcp_cubic.c. The purpose is mainly for testing
5 * the kernel BPF logic.
6 *
7 * Highlights:
8 * 1. CONFIG_HZ .kconfig map is used.
9 * 2. In bictcp_update(), calculation is changed to use usec
10 * resolution (i.e. USEC_PER_JIFFY) instead of using jiffies.
11 * Thus, usecs_to_jiffies() is not used in the bpf_cubic.c.
12 * 3. In bitctcp_update() [under tcp_friendliness], the original
13 * "while (ca->ack_cnt > delta)" loop is changed to the equivalent
14 * "ca->ack_cnt / delta" operation.
15 */
16
17 #include "bpf_tracing_net.h"
18 #include <bpf/bpf_tracing.h>
19
20 char _license[] SEC("license") = "GPL";
21
22 #define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
23
24 extern __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked) __ksym;
25 extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;
26
27 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
28 * max_cwnd = snd_cwnd * beta
29 */
30 #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
31
32 /* Two methods of hybrid slow start */
33 #define HYSTART_ACK_TRAIN 0x1
34 #define HYSTART_DELAY 0x2
35
36 /* Number of delay samples for detecting the increase of delay */
37 #define HYSTART_MIN_SAMPLES 8
38 #define HYSTART_DELAY_MIN (4000U) /* 4ms */
39 #define HYSTART_DELAY_MAX (16000U) /* 16 ms */
40 #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
41
42 static int fast_convergence = 1;
43 static const int beta = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
44 static int initial_ssthresh;
45 static const int bic_scale = 41;
46 static int tcp_friendliness = 1;
47
48 static int hystart = 1;
49 static int hystart_detect = HYSTART_ACK_TRAIN | HYSTART_DELAY;
50 static int hystart_low_window = 16;
51 static int hystart_ack_delta_us = 2000;
52
53 static const __u32 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
54 static const __u32 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
55 / (BICTCP_BETA_SCALE - beta);
56 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
57 * so K = cubic_root( (wmax-cwnd)*rtt/c )
58 * the unit of K is bictcp_HZ=2^10, not HZ
59 *
60 * c = bic_scale >> 10
61 * rtt = 100ms
62 *
63 * the following code has been designed and tested for
64 * cwnd < 1 million packets
65 * RTT < 100 seconds
66 * HZ < 1,000,00 (corresponding to 10 nano-second)
67 */
68
69 /* 1/c * 2^2*bictcp_HZ * srtt, 2^40 */
70 static const __u64 cube_factor = (__u64)(1ull << (10+3*BICTCP_HZ))
71 / (bic_scale * 10);
72
73 /* BIC TCP Parameters */
74 struct bpf_bictcp {
75 __u32 cnt; /* increase cwnd by 1 after ACKs */
76 __u32 last_max_cwnd; /* last maximum snd_cwnd */
77 __u32 last_cwnd; /* the last snd_cwnd */
78 __u32 last_time; /* time when updated last_cwnd */
79 __u32 bic_origin_point;/* origin point of bic function */
80 __u32 bic_K; /* time to origin point
81 from the beginning of the current epoch */
82 __u32 delay_min; /* min delay (usec) */
83 __u32 epoch_start; /* beginning of an epoch */
84 __u32 ack_cnt; /* number of acks */
85 __u32 tcp_cwnd; /* estimated tcp cwnd */
86 __u16 unused;
87 __u8 sample_cnt; /* number of samples to decide curr_rtt */
88 __u8 found; /* the exit point is found? */
89 __u32 round_start; /* beginning of each round */
90 __u32 end_seq; /* end_seq of the round */
91 __u32 last_ack; /* last time when the ACK spacing is close */
92 __u32 curr_rtt; /* the minimum rtt of current round */
93 };
94
bictcp_reset(struct bpf_bictcp * ca)95 static void bictcp_reset(struct bpf_bictcp *ca)
96 {
97 ca->cnt = 0;
98 ca->last_max_cwnd = 0;
99 ca->last_cwnd = 0;
100 ca->last_time = 0;
101 ca->bic_origin_point = 0;
102 ca->bic_K = 0;
103 ca->delay_min = 0;
104 ca->epoch_start = 0;
105 ca->ack_cnt = 0;
106 ca->tcp_cwnd = 0;
107 ca->found = 0;
108 }
109
110 extern unsigned long CONFIG_HZ __kconfig;
111 #define HZ CONFIG_HZ
112 #define USEC_PER_MSEC 1000UL
113 #define USEC_PER_SEC 1000000UL
114 #define USEC_PER_JIFFY (USEC_PER_SEC / HZ)
115
div64_u64(__u64 dividend,__u64 divisor)116 static __u64 div64_u64(__u64 dividend, __u64 divisor)
117 {
118 return dividend / divisor;
119 }
120
121 #define div64_ul div64_u64
122
123 #define BITS_PER_U64 (sizeof(__u64) * 8)
fls64(__u64 x)124 static int fls64(__u64 x)
125 {
126 int num = BITS_PER_U64 - 1;
127
128 if (x == 0)
129 return 0;
130
131 if (!(x & (~0ull << (BITS_PER_U64-32)))) {
132 num -= 32;
133 x <<= 32;
134 }
135 if (!(x & (~0ull << (BITS_PER_U64-16)))) {
136 num -= 16;
137 x <<= 16;
138 }
139 if (!(x & (~0ull << (BITS_PER_U64-8)))) {
140 num -= 8;
141 x <<= 8;
142 }
143 if (!(x & (~0ull << (BITS_PER_U64-4)))) {
144 num -= 4;
145 x <<= 4;
146 }
147 if (!(x & (~0ull << (BITS_PER_U64-2)))) {
148 num -= 2;
149 x <<= 2;
150 }
151 if (!(x & (~0ull << (BITS_PER_U64-1))))
152 num -= 1;
153
154 return num + 1;
155 }
156
bictcp_clock_us(const struct sock * sk)157 static __u32 bictcp_clock_us(const struct sock *sk)
158 {
159 return tcp_sk(sk)->tcp_mstamp;
160 }
161
bictcp_hystart_reset(struct sock * sk)162 static void bictcp_hystart_reset(struct sock *sk)
163 {
164 struct tcp_sock *tp = tcp_sk(sk);
165 struct bpf_bictcp *ca = inet_csk_ca(sk);
166
167 ca->round_start = ca->last_ack = bictcp_clock_us(sk);
168 ca->end_seq = tp->snd_nxt;
169 ca->curr_rtt = ~0U;
170 ca->sample_cnt = 0;
171 }
172
173 SEC("struct_ops")
BPF_PROG(bpf_cubic_init,struct sock * sk)174 void BPF_PROG(bpf_cubic_init, struct sock *sk)
175 {
176 struct bpf_bictcp *ca = inet_csk_ca(sk);
177
178 bictcp_reset(ca);
179
180 if (hystart)
181 bictcp_hystart_reset(sk);
182
183 if (!hystart && initial_ssthresh)
184 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
185 }
186
187 SEC("struct_ops")
BPF_PROG(bpf_cubic_cwnd_event,struct sock * sk,enum tcp_ca_event event)188 void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event)
189 {
190 if (event == CA_EVENT_TX_START) {
191 struct bpf_bictcp *ca = inet_csk_ca(sk);
192 __u32 now = tcp_jiffies32;
193 __s32 delta;
194
195 delta = now - tcp_sk(sk)->lsndtime;
196
197 /* We were application limited (idle) for a while.
198 * Shift epoch_start to keep cwnd growth to cubic curve.
199 */
200 if (ca->epoch_start && delta > 0) {
201 ca->epoch_start += delta;
202 if (after(ca->epoch_start, now))
203 ca->epoch_start = now;
204 }
205 return;
206 }
207 }
208
209 /*
210 * cbrt(x) MSB values for x MSB values in [0..63].
211 * Precomputed then refined by hand - Willy Tarreau
212 *
213 * For x in [0..63],
214 * v = cbrt(x << 18) - 1
215 * cbrt(x) = (v[x] + 10) >> 6
216 */
217 static const __u8 v[] = {
218 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
219 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
220 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
221 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
222 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
223 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
224 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
225 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
226 };
227
228 /* calculate the cubic root of x using a table lookup followed by one
229 * Newton-Raphson iteration.
230 * Avg err ~= 0.195%
231 */
cubic_root(__u64 a)232 static __u32 cubic_root(__u64 a)
233 {
234 __u32 x, b, shift;
235
236 if (a < 64) {
237 /* a in [0..63] */
238 return ((__u32)v[(__u32)a] + 35) >> 6;
239 }
240
241 b = fls64(a);
242 b = ((b * 84) >> 8) - 1;
243 shift = (a >> (b * 3));
244
245 /* it is needed for verifier's bound check on v */
246 if (shift >= 64)
247 return 0;
248
249 x = ((__u32)(((__u32)v[shift] + 10) << b)) >> 6;
250
251 /*
252 * Newton-Raphson iteration
253 * 2
254 * x = ( 2 * x + a / x ) / 3
255 * k+1 k k
256 */
257 x = (2 * x + (__u32)div64_u64(a, (__u64)x * (__u64)(x - 1)));
258 x = ((x * 341) >> 10);
259 return x;
260 }
261
262 /*
263 * Compute congestion window to use.
264 */
bictcp_update(struct bpf_bictcp * ca,__u32 cwnd,__u32 acked)265 static void bictcp_update(struct bpf_bictcp *ca, __u32 cwnd, __u32 acked)
266 {
267 __u32 delta, bic_target, max_cnt;
268 __u64 offs, t;
269
270 ca->ack_cnt += acked; /* count the number of ACKed packets */
271
272 if (ca->last_cwnd == cwnd &&
273 (__s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
274 return;
275
276 /* The CUBIC function can update ca->cnt at most once per jiffy.
277 * On all cwnd reduction events, ca->epoch_start is set to 0,
278 * which will force a recalculation of ca->cnt.
279 */
280 if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
281 goto tcp_friendliness;
282
283 ca->last_cwnd = cwnd;
284 ca->last_time = tcp_jiffies32;
285
286 if (ca->epoch_start == 0) {
287 ca->epoch_start = tcp_jiffies32; /* record beginning */
288 ca->ack_cnt = acked; /* start counting */
289 ca->tcp_cwnd = cwnd; /* syn with cubic */
290
291 if (ca->last_max_cwnd <= cwnd) {
292 ca->bic_K = 0;
293 ca->bic_origin_point = cwnd;
294 } else {
295 /* Compute new K based on
296 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
297 */
298 ca->bic_K = cubic_root(cube_factor
299 * (ca->last_max_cwnd - cwnd));
300 ca->bic_origin_point = ca->last_max_cwnd;
301 }
302 }
303
304 /* cubic function - calc*/
305 /* calculate c * time^3 / rtt,
306 * while considering overflow in calculation of time^3
307 * (so time^3 is done by using 64 bit)
308 * and without the support of division of 64bit numbers
309 * (so all divisions are done by using 32 bit)
310 * also NOTE the unit of those variables
311 * time = (t - K) / 2^bictcp_HZ
312 * c = bic_scale >> 10
313 * rtt = (srtt >> 3) / HZ
314 * !!! The following code does not have overflow problems,
315 * if the cwnd < 1 million packets !!!
316 */
317
318 t = (__s32)(tcp_jiffies32 - ca->epoch_start) * USEC_PER_JIFFY;
319 t += ca->delay_min;
320 /* change the unit from usec to bictcp_HZ */
321 t <<= BICTCP_HZ;
322 t /= USEC_PER_SEC;
323
324 if (t < ca->bic_K) /* t - K */
325 offs = ca->bic_K - t;
326 else
327 offs = t - ca->bic_K;
328
329 /* c/rtt * (t-K)^3 */
330 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
331 if (t < ca->bic_K) /* below origin*/
332 bic_target = ca->bic_origin_point - delta;
333 else /* above origin*/
334 bic_target = ca->bic_origin_point + delta;
335
336 /* cubic function - calc bictcp_cnt*/
337 if (bic_target > cwnd) {
338 ca->cnt = cwnd / (bic_target - cwnd);
339 } else {
340 ca->cnt = 100 * cwnd; /* very small increment*/
341 }
342
343 /*
344 * The initial growth of cubic function may be too conservative
345 * when the available bandwidth is still unknown.
346 */
347 if (ca->last_max_cwnd == 0 && ca->cnt > 20)
348 ca->cnt = 20; /* increase cwnd 5% per RTT */
349
350 tcp_friendliness:
351 /* TCP Friendly */
352 if (tcp_friendliness) {
353 __u32 scale = beta_scale;
354 __u32 n;
355
356 /* update tcp cwnd */
357 delta = (cwnd * scale) >> 3;
358 if (ca->ack_cnt > delta && delta) {
359 n = ca->ack_cnt / delta;
360 ca->ack_cnt -= n * delta;
361 ca->tcp_cwnd += n;
362 }
363
364 if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
365 delta = ca->tcp_cwnd - cwnd;
366 max_cnt = cwnd / delta;
367 if (ca->cnt > max_cnt)
368 ca->cnt = max_cnt;
369 }
370 }
371
372 /* The maximum rate of cwnd increase CUBIC allows is 1 packet per
373 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
374 */
375 ca->cnt = max(ca->cnt, 2U);
376 }
377
378 SEC("struct_ops")
BPF_PROG(bpf_cubic_cong_avoid,struct sock * sk,__u32 ack,__u32 acked)379 void BPF_PROG(bpf_cubic_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
380 {
381 struct tcp_sock *tp = tcp_sk(sk);
382 struct bpf_bictcp *ca = inet_csk_ca(sk);
383
384 if (!tcp_is_cwnd_limited(sk))
385 return;
386
387 if (tcp_in_slow_start(tp)) {
388 if (hystart && after(ack, ca->end_seq))
389 bictcp_hystart_reset(sk);
390 acked = tcp_slow_start(tp, acked);
391 if (!acked)
392 return;
393 }
394 bictcp_update(ca, tp->snd_cwnd, acked);
395 tcp_cong_avoid_ai(tp, ca->cnt, acked);
396 }
397
398 SEC("struct_ops")
BPF_PROG(bpf_cubic_recalc_ssthresh,struct sock * sk)399 __u32 BPF_PROG(bpf_cubic_recalc_ssthresh, struct sock *sk)
400 {
401 const struct tcp_sock *tp = tcp_sk(sk);
402 struct bpf_bictcp *ca = inet_csk_ca(sk);
403
404 ca->epoch_start = 0; /* end of epoch */
405
406 /* Wmax and fast convergence */
407 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
408 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
409 / (2 * BICTCP_BETA_SCALE);
410 else
411 ca->last_max_cwnd = tp->snd_cwnd;
412
413 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
414 }
415
416 SEC("struct_ops")
BPF_PROG(bpf_cubic_state,struct sock * sk,__u8 new_state)417 void BPF_PROG(bpf_cubic_state, struct sock *sk, __u8 new_state)
418 {
419 if (new_state == TCP_CA_Loss) {
420 bictcp_reset(inet_csk_ca(sk));
421 bictcp_hystart_reset(sk);
422 }
423 }
424
425 #define GSO_MAX_SIZE 65536
426
427 /* Account for TSO/GRO delays.
428 * Otherwise short RTT flows could get too small ssthresh, since during
429 * slow start we begin with small TSO packets and ca->delay_min would
430 * not account for long aggregation delay when TSO packets get bigger.
431 * Ideally even with a very small RTT we would like to have at least one
432 * TSO packet being sent and received by GRO, and another one in qdisc layer.
433 * We apply another 100% factor because @rate is doubled at this point.
434 * We cap the cushion to 1ms.
435 */
hystart_ack_delay(struct sock * sk)436 static __u32 hystart_ack_delay(struct sock *sk)
437 {
438 unsigned long rate;
439
440 rate = sk->sk_pacing_rate;
441 if (!rate)
442 return 0;
443 return min((__u64)USEC_PER_MSEC,
444 div64_ul((__u64)GSO_MAX_SIZE * 4 * USEC_PER_SEC, rate));
445 }
446
hystart_update(struct sock * sk,__u32 delay)447 static void hystart_update(struct sock *sk, __u32 delay)
448 {
449 struct tcp_sock *tp = tcp_sk(sk);
450 struct bpf_bictcp *ca = inet_csk_ca(sk);
451 __u32 threshold;
452
453 if (hystart_detect & HYSTART_ACK_TRAIN) {
454 __u32 now = bictcp_clock_us(sk);
455
456 /* first detection parameter - ack-train detection */
457 if ((__s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
458 ca->last_ack = now;
459
460 threshold = ca->delay_min + hystart_ack_delay(sk);
461
462 /* Hystart ack train triggers if we get ack past
463 * ca->delay_min/2.
464 * Pacing might have delayed packets up to RTT/2
465 * during slow start.
466 */
467 if (sk->sk_pacing_status == SK_PACING_NONE)
468 threshold >>= 1;
469
470 if ((__s32)(now - ca->round_start) > threshold) {
471 ca->found = 1;
472 tp->snd_ssthresh = tp->snd_cwnd;
473 }
474 }
475 }
476
477 if (hystart_detect & HYSTART_DELAY) {
478 /* obtain the minimum delay of more than sampling packets */
479 if (ca->curr_rtt > delay)
480 ca->curr_rtt = delay;
481 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
482 ca->sample_cnt++;
483 } else {
484 if (ca->curr_rtt > ca->delay_min +
485 HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
486 ca->found = 1;
487 tp->snd_ssthresh = tp->snd_cwnd;
488 }
489 }
490 }
491 }
492
493 int bpf_cubic_acked_called = 0;
494
495 SEC("struct_ops")
BPF_PROG(bpf_cubic_acked,struct sock * sk,const struct ack_sample * sample)496 void BPF_PROG(bpf_cubic_acked, struct sock *sk, const struct ack_sample *sample)
497 {
498 const struct tcp_sock *tp = tcp_sk(sk);
499 struct bpf_bictcp *ca = inet_csk_ca(sk);
500 __u32 delay;
501
502 bpf_cubic_acked_called = 1;
503 /* Some calls are for duplicates without timestamps */
504 if (sample->rtt_us < 0)
505 return;
506
507 /* Discard delay samples right after fast recovery */
508 if (ca->epoch_start && (__s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
509 return;
510
511 delay = sample->rtt_us;
512 if (delay == 0)
513 delay = 1;
514
515 /* first time call or link delay decreases */
516 if (ca->delay_min == 0 || ca->delay_min > delay)
517 ca->delay_min = delay;
518
519 /* hystart triggers when cwnd is larger than some threshold */
520 if (!ca->found && tcp_in_slow_start(tp) && hystart &&
521 tp->snd_cwnd >= hystart_low_window)
522 hystart_update(sk, delay);
523 }
524
525 extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;
526
527 SEC("struct_ops")
BPF_PROG(bpf_cubic_undo_cwnd,struct sock * sk)528 __u32 BPF_PROG(bpf_cubic_undo_cwnd, struct sock *sk)
529 {
530 return tcp_reno_undo_cwnd(sk);
531 }
532
533 SEC(".struct_ops")
534 struct tcp_congestion_ops cubic = {
535 .init = (void *)bpf_cubic_init,
536 .ssthresh = (void *)bpf_cubic_recalc_ssthresh,
537 .cong_avoid = (void *)bpf_cubic_cong_avoid,
538 .set_state = (void *)bpf_cubic_state,
539 .undo_cwnd = (void *)bpf_cubic_undo_cwnd,
540 .cwnd_event = (void *)bpf_cubic_cwnd_event,
541 .pkts_acked = (void *)bpf_cubic_acked,
542 .name = "bpf_cubic",
543 };
544