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 #define min(a, b) ((a) < (b) ? (a) : (b))
24 #define max(a, b) ((a) > (b) ? (a) : (b))
before(__u32 seq1,__u32 seq2)25 static bool before(__u32 seq1, __u32 seq2)
26 {
27 return (__s32)(seq1-seq2) < 0;
28 }
29 #define after(seq2, seq1) before(seq1, seq2)
30
31 extern __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked) __ksym;
32 extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;
33
34 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
35 * max_cwnd = snd_cwnd * beta
36 */
37 #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
38
39 /* Two methods of hybrid slow start */
40 #define HYSTART_ACK_TRAIN 0x1
41 #define HYSTART_DELAY 0x2
42
43 /* Number of delay samples for detecting the increase of delay */
44 #define HYSTART_MIN_SAMPLES 8
45 #define HYSTART_DELAY_MIN (4000U) /* 4ms */
46 #define HYSTART_DELAY_MAX (16000U) /* 16 ms */
47 #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
48
49 static int fast_convergence = 1;
50 static const int beta = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
51 static int initial_ssthresh;
52 static const int bic_scale = 41;
53 static int tcp_friendliness = 1;
54
55 static int hystart = 1;
56 static int hystart_detect = HYSTART_ACK_TRAIN | HYSTART_DELAY;
57 static int hystart_low_window = 16;
58 static int hystart_ack_delta_us = 2000;
59
60 static const __u32 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
61 static const __u32 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
62 / (BICTCP_BETA_SCALE - beta);
63 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
64 * so K = cubic_root( (wmax-cwnd)*rtt/c )
65 * the unit of K is bictcp_HZ=2^10, not HZ
66 *
67 * c = bic_scale >> 10
68 * rtt = 100ms
69 *
70 * the following code has been designed and tested for
71 * cwnd < 1 million packets
72 * RTT < 100 seconds
73 * HZ < 1,000,00 (corresponding to 10 nano-second)
74 */
75
76 /* 1/c * 2^2*bictcp_HZ * srtt, 2^40 */
77 static const __u64 cube_factor = (__u64)(1ull << (10+3*BICTCP_HZ))
78 / (bic_scale * 10);
79
80 /* BIC TCP Parameters */
81 struct bpf_bictcp {
82 __u32 cnt; /* increase cwnd by 1 after ACKs */
83 __u32 last_max_cwnd; /* last maximum snd_cwnd */
84 __u32 last_cwnd; /* the last snd_cwnd */
85 __u32 last_time; /* time when updated last_cwnd */
86 __u32 bic_origin_point;/* origin point of bic function */
87 __u32 bic_K; /* time to origin point
88 from the beginning of the current epoch */
89 __u32 delay_min; /* min delay (usec) */
90 __u32 epoch_start; /* beginning of an epoch */
91 __u32 ack_cnt; /* number of acks */
92 __u32 tcp_cwnd; /* estimated tcp cwnd */
93 __u16 unused;
94 __u8 sample_cnt; /* number of samples to decide curr_rtt */
95 __u8 found; /* the exit point is found? */
96 __u32 round_start; /* beginning of each round */
97 __u32 end_seq; /* end_seq of the round */
98 __u32 last_ack; /* last time when the ACK spacing is close */
99 __u32 curr_rtt; /* the minimum rtt of current round */
100 };
101
bictcp_reset(struct bpf_bictcp * ca)102 static void bictcp_reset(struct bpf_bictcp *ca)
103 {
104 ca->cnt = 0;
105 ca->last_max_cwnd = 0;
106 ca->last_cwnd = 0;
107 ca->last_time = 0;
108 ca->bic_origin_point = 0;
109 ca->bic_K = 0;
110 ca->delay_min = 0;
111 ca->epoch_start = 0;
112 ca->ack_cnt = 0;
113 ca->tcp_cwnd = 0;
114 ca->found = 0;
115 }
116
117 extern unsigned long CONFIG_HZ __kconfig;
118 #define HZ CONFIG_HZ
119 #define USEC_PER_MSEC 1000UL
120 #define USEC_PER_SEC 1000000UL
121 #define USEC_PER_JIFFY (USEC_PER_SEC / HZ)
122
div64_u64(__u64 dividend,__u64 divisor)123 static __u64 div64_u64(__u64 dividend, __u64 divisor)
124 {
125 return dividend / divisor;
126 }
127
128 #define div64_ul div64_u64
129
130 #define BITS_PER_U64 (sizeof(__u64) * 8)
fls64(__u64 x)131 static int fls64(__u64 x)
132 {
133 int num = BITS_PER_U64 - 1;
134
135 if (x == 0)
136 return 0;
137
138 if (!(x & (~0ull << (BITS_PER_U64-32)))) {
139 num -= 32;
140 x <<= 32;
141 }
142 if (!(x & (~0ull << (BITS_PER_U64-16)))) {
143 num -= 16;
144 x <<= 16;
145 }
146 if (!(x & (~0ull << (BITS_PER_U64-8)))) {
147 num -= 8;
148 x <<= 8;
149 }
150 if (!(x & (~0ull << (BITS_PER_U64-4)))) {
151 num -= 4;
152 x <<= 4;
153 }
154 if (!(x & (~0ull << (BITS_PER_U64-2)))) {
155 num -= 2;
156 x <<= 2;
157 }
158 if (!(x & (~0ull << (BITS_PER_U64-1))))
159 num -= 1;
160
161 return num + 1;
162 }
163
bictcp_clock_us(const struct sock * sk)164 static __u32 bictcp_clock_us(const struct sock *sk)
165 {
166 return tcp_sk(sk)->tcp_mstamp;
167 }
168
bictcp_hystart_reset(struct sock * sk)169 static void bictcp_hystart_reset(struct sock *sk)
170 {
171 struct tcp_sock *tp = tcp_sk(sk);
172 struct bpf_bictcp *ca = inet_csk_ca(sk);
173
174 ca->round_start = ca->last_ack = bictcp_clock_us(sk);
175 ca->end_seq = tp->snd_nxt;
176 ca->curr_rtt = ~0U;
177 ca->sample_cnt = 0;
178 }
179
180 SEC("struct_ops")
BPF_PROG(bpf_cubic_init,struct sock * sk)181 void BPF_PROG(bpf_cubic_init, struct sock *sk)
182 {
183 struct bpf_bictcp *ca = inet_csk_ca(sk);
184
185 bictcp_reset(ca);
186
187 if (hystart)
188 bictcp_hystart_reset(sk);
189
190 if (!hystart && initial_ssthresh)
191 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
192 }
193
194 SEC("struct_ops")
BPF_PROG(bpf_cubic_cwnd_event,struct sock * sk,enum tcp_ca_event event)195 void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event)
196 {
197 if (event == CA_EVENT_TX_START) {
198 struct bpf_bictcp *ca = inet_csk_ca(sk);
199 __u32 now = tcp_jiffies32;
200 __s32 delta;
201
202 delta = now - tcp_sk(sk)->lsndtime;
203
204 /* We were application limited (idle) for a while.
205 * Shift epoch_start to keep cwnd growth to cubic curve.
206 */
207 if (ca->epoch_start && delta > 0) {
208 ca->epoch_start += delta;
209 if (after(ca->epoch_start, now))
210 ca->epoch_start = now;
211 }
212 return;
213 }
214 }
215
216 /*
217 * cbrt(x) MSB values for x MSB values in [0..63].
218 * Precomputed then refined by hand - Willy Tarreau
219 *
220 * For x in [0..63],
221 * v = cbrt(x << 18) - 1
222 * cbrt(x) = (v[x] + 10) >> 6
223 */
224 static const __u8 v[] = {
225 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
226 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
227 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
228 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
229 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
230 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
231 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
232 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
233 };
234
235 /* calculate the cubic root of x using a table lookup followed by one
236 * Newton-Raphson iteration.
237 * Avg err ~= 0.195%
238 */
cubic_root(__u64 a)239 static __u32 cubic_root(__u64 a)
240 {
241 __u32 x, b, shift;
242
243 if (a < 64) {
244 /* a in [0..63] */
245 return ((__u32)v[(__u32)a] + 35) >> 6;
246 }
247
248 b = fls64(a);
249 b = ((b * 84) >> 8) - 1;
250 shift = (a >> (b * 3));
251
252 /* it is needed for verifier's bound check on v */
253 if (shift >= 64)
254 return 0;
255
256 x = ((__u32)(((__u32)v[shift] + 10) << b)) >> 6;
257
258 /*
259 * Newton-Raphson iteration
260 * 2
261 * x = ( 2 * x + a / x ) / 3
262 * k+1 k k
263 */
264 x = (2 * x + (__u32)div64_u64(a, (__u64)x * (__u64)(x - 1)));
265 x = ((x * 341) >> 10);
266 return x;
267 }
268
269 /*
270 * Compute congestion window to use.
271 */
bictcp_update(struct bpf_bictcp * ca,__u32 cwnd,__u32 acked)272 static void bictcp_update(struct bpf_bictcp *ca, __u32 cwnd, __u32 acked)
273 {
274 __u32 delta, bic_target, max_cnt;
275 __u64 offs, t;
276
277 ca->ack_cnt += acked; /* count the number of ACKed packets */
278
279 if (ca->last_cwnd == cwnd &&
280 (__s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
281 return;
282
283 /* The CUBIC function can update ca->cnt at most once per jiffy.
284 * On all cwnd reduction events, ca->epoch_start is set to 0,
285 * which will force a recalculation of ca->cnt.
286 */
287 if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
288 goto tcp_friendliness;
289
290 ca->last_cwnd = cwnd;
291 ca->last_time = tcp_jiffies32;
292
293 if (ca->epoch_start == 0) {
294 ca->epoch_start = tcp_jiffies32; /* record beginning */
295 ca->ack_cnt = acked; /* start counting */
296 ca->tcp_cwnd = cwnd; /* syn with cubic */
297
298 if (ca->last_max_cwnd <= cwnd) {
299 ca->bic_K = 0;
300 ca->bic_origin_point = cwnd;
301 } else {
302 /* Compute new K based on
303 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
304 */
305 ca->bic_K = cubic_root(cube_factor
306 * (ca->last_max_cwnd - cwnd));
307 ca->bic_origin_point = ca->last_max_cwnd;
308 }
309 }
310
311 /* cubic function - calc*/
312 /* calculate c * time^3 / rtt,
313 * while considering overflow in calculation of time^3
314 * (so time^3 is done by using 64 bit)
315 * and without the support of division of 64bit numbers
316 * (so all divisions are done by using 32 bit)
317 * also NOTE the unit of those variables
318 * time = (t - K) / 2^bictcp_HZ
319 * c = bic_scale >> 10
320 * rtt = (srtt >> 3) / HZ
321 * !!! The following code does not have overflow problems,
322 * if the cwnd < 1 million packets !!!
323 */
324
325 t = (__s32)(tcp_jiffies32 - ca->epoch_start) * USEC_PER_JIFFY;
326 t += ca->delay_min;
327 /* change the unit from usec to bictcp_HZ */
328 t <<= BICTCP_HZ;
329 t /= USEC_PER_SEC;
330
331 if (t < ca->bic_K) /* t - K */
332 offs = ca->bic_K - t;
333 else
334 offs = t - ca->bic_K;
335
336 /* c/rtt * (t-K)^3 */
337 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
338 if (t < ca->bic_K) /* below origin*/
339 bic_target = ca->bic_origin_point - delta;
340 else /* above origin*/
341 bic_target = ca->bic_origin_point + delta;
342
343 /* cubic function - calc bictcp_cnt*/
344 if (bic_target > cwnd) {
345 ca->cnt = cwnd / (bic_target - cwnd);
346 } else {
347 ca->cnt = 100 * cwnd; /* very small increment*/
348 }
349
350 /*
351 * The initial growth of cubic function may be too conservative
352 * when the available bandwidth is still unknown.
353 */
354 if (ca->last_max_cwnd == 0 && ca->cnt > 20)
355 ca->cnt = 20; /* increase cwnd 5% per RTT */
356
357 tcp_friendliness:
358 /* TCP Friendly */
359 if (tcp_friendliness) {
360 __u32 scale = beta_scale;
361 __u32 n;
362
363 /* update tcp cwnd */
364 delta = (cwnd * scale) >> 3;
365 if (ca->ack_cnt > delta && delta) {
366 n = ca->ack_cnt / delta;
367 ca->ack_cnt -= n * delta;
368 ca->tcp_cwnd += n;
369 }
370
371 if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
372 delta = ca->tcp_cwnd - cwnd;
373 max_cnt = cwnd / delta;
374 if (ca->cnt > max_cnt)
375 ca->cnt = max_cnt;
376 }
377 }
378
379 /* The maximum rate of cwnd increase CUBIC allows is 1 packet per
380 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
381 */
382 ca->cnt = max(ca->cnt, 2U);
383 }
384
385 SEC("struct_ops")
BPF_PROG(bpf_cubic_cong_avoid,struct sock * sk,__u32 ack,__u32 acked)386 void BPF_PROG(bpf_cubic_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
387 {
388 struct tcp_sock *tp = tcp_sk(sk);
389 struct bpf_bictcp *ca = inet_csk_ca(sk);
390
391 if (!tcp_is_cwnd_limited(sk))
392 return;
393
394 if (tcp_in_slow_start(tp)) {
395 if (hystart && after(ack, ca->end_seq))
396 bictcp_hystart_reset(sk);
397 acked = tcp_slow_start(tp, acked);
398 if (!acked)
399 return;
400 }
401 bictcp_update(ca, tp->snd_cwnd, acked);
402 tcp_cong_avoid_ai(tp, ca->cnt, acked);
403 }
404
405 SEC("struct_ops")
BPF_PROG(bpf_cubic_recalc_ssthresh,struct sock * sk)406 __u32 BPF_PROG(bpf_cubic_recalc_ssthresh, struct sock *sk)
407 {
408 const struct tcp_sock *tp = tcp_sk(sk);
409 struct bpf_bictcp *ca = inet_csk_ca(sk);
410
411 ca->epoch_start = 0; /* end of epoch */
412
413 /* Wmax and fast convergence */
414 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
415 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
416 / (2 * BICTCP_BETA_SCALE);
417 else
418 ca->last_max_cwnd = tp->snd_cwnd;
419
420 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
421 }
422
423 SEC("struct_ops")
BPF_PROG(bpf_cubic_state,struct sock * sk,__u8 new_state)424 void BPF_PROG(bpf_cubic_state, struct sock *sk, __u8 new_state)
425 {
426 if (new_state == TCP_CA_Loss) {
427 bictcp_reset(inet_csk_ca(sk));
428 bictcp_hystart_reset(sk);
429 }
430 }
431
432 #define GSO_MAX_SIZE 65536
433
434 /* Account for TSO/GRO delays.
435 * Otherwise short RTT flows could get too small ssthresh, since during
436 * slow start we begin with small TSO packets and ca->delay_min would
437 * not account for long aggregation delay when TSO packets get bigger.
438 * Ideally even with a very small RTT we would like to have at least one
439 * TSO packet being sent and received by GRO, and another one in qdisc layer.
440 * We apply another 100% factor because @rate is doubled at this point.
441 * We cap the cushion to 1ms.
442 */
hystart_ack_delay(struct sock * sk)443 static __u32 hystart_ack_delay(struct sock *sk)
444 {
445 unsigned long rate;
446
447 rate = sk->sk_pacing_rate;
448 if (!rate)
449 return 0;
450 return min((__u64)USEC_PER_MSEC,
451 div64_ul((__u64)GSO_MAX_SIZE * 4 * USEC_PER_SEC, rate));
452 }
453
hystart_update(struct sock * sk,__u32 delay)454 static void hystart_update(struct sock *sk, __u32 delay)
455 {
456 struct tcp_sock *tp = tcp_sk(sk);
457 struct bpf_bictcp *ca = inet_csk_ca(sk);
458 __u32 threshold;
459
460 if (hystart_detect & HYSTART_ACK_TRAIN) {
461 __u32 now = bictcp_clock_us(sk);
462
463 /* first detection parameter - ack-train detection */
464 if ((__s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
465 ca->last_ack = now;
466
467 threshold = ca->delay_min + hystart_ack_delay(sk);
468
469 /* Hystart ack train triggers if we get ack past
470 * ca->delay_min/2.
471 * Pacing might have delayed packets up to RTT/2
472 * during slow start.
473 */
474 if (sk->sk_pacing_status == SK_PACING_NONE)
475 threshold >>= 1;
476
477 if ((__s32)(now - ca->round_start) > threshold) {
478 ca->found = 1;
479 tp->snd_ssthresh = tp->snd_cwnd;
480 }
481 }
482 }
483
484 if (hystart_detect & HYSTART_DELAY) {
485 /* obtain the minimum delay of more than sampling packets */
486 if (ca->curr_rtt > delay)
487 ca->curr_rtt = delay;
488 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
489 ca->sample_cnt++;
490 } else {
491 if (ca->curr_rtt > ca->delay_min +
492 HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
493 ca->found = 1;
494 tp->snd_ssthresh = tp->snd_cwnd;
495 }
496 }
497 }
498 }
499
500 int bpf_cubic_acked_called = 0;
501
502 SEC("struct_ops")
BPF_PROG(bpf_cubic_acked,struct sock * sk,const struct ack_sample * sample)503 void BPF_PROG(bpf_cubic_acked, struct sock *sk, const struct ack_sample *sample)
504 {
505 const struct tcp_sock *tp = tcp_sk(sk);
506 struct bpf_bictcp *ca = inet_csk_ca(sk);
507 __u32 delay;
508
509 bpf_cubic_acked_called = 1;
510 /* Some calls are for duplicates without timestamps */
511 if (sample->rtt_us < 0)
512 return;
513
514 /* Discard delay samples right after fast recovery */
515 if (ca->epoch_start && (__s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
516 return;
517
518 delay = sample->rtt_us;
519 if (delay == 0)
520 delay = 1;
521
522 /* first time call or link delay decreases */
523 if (ca->delay_min == 0 || ca->delay_min > delay)
524 ca->delay_min = delay;
525
526 /* hystart triggers when cwnd is larger than some threshold */
527 if (!ca->found && tcp_in_slow_start(tp) && hystart &&
528 tp->snd_cwnd >= hystart_low_window)
529 hystart_update(sk, delay);
530 }
531
532 extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;
533
534 SEC("struct_ops")
BPF_PROG(bpf_cubic_undo_cwnd,struct sock * sk)535 __u32 BPF_PROG(bpf_cubic_undo_cwnd, struct sock *sk)
536 {
537 return tcp_reno_undo_cwnd(sk);
538 }
539
540 SEC(".struct_ops")
541 struct tcp_congestion_ops cubic = {
542 .init = (void *)bpf_cubic_init,
543 .ssthresh = (void *)bpf_cubic_recalc_ssthresh,
544 .cong_avoid = (void *)bpf_cubic_cong_avoid,
545 .set_state = (void *)bpf_cubic_state,
546 .undo_cwnd = (void *)bpf_cubic_undo_cwnd,
547 .cwnd_event = (void *)bpf_cubic_cwnd_event,
548 .pkts_acked = (void *)bpf_cubic_acked,
549 .name = "bpf_cubic",
550 };
551