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1// SPDX-License-Identifier: GPL-2.0-only2 3/* WARNING: This implementation is not necessarily the same4 * as the tcp_cubic.c. The purpose is mainly for testing5 * 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 usec10 * 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 original13 * "while (ca->ack_cnt > delta)" loop is changed to the equivalent14 * "ca->ack_cnt / delta" operation.15 */16 17#include "bpf_tracing_net.h"18#include <bpf/bpf_tracing.h>19 20char _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))25static bool before(__u32 seq1, __u32 seq2)26{27 return (__s32)(seq1-seq2) < 0;28}29#define after(seq2, seq1) before(seq1, seq2)30 31extern __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked) __ksym;32extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;33 34#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation35 * max_cwnd = snd_cwnd * beta36 */37#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */38 39/* Two methods of hybrid slow start */40#define HYSTART_ACK_TRAIN 0x141#define HYSTART_DELAY 0x242 43/* Number of delay samples for detecting the increase of delay */44#define HYSTART_MIN_SAMPLES 845#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 49static int fast_convergence = 1;50static const int beta = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */51static int initial_ssthresh;52static const int bic_scale = 41;53static int tcp_friendliness = 1;54 55static int hystart = 1;56static int hystart_detect = HYSTART_ACK_TRAIN | HYSTART_DELAY;57static int hystart_low_window = 16;58static int hystart_ack_delta_us = 2000;59 60static const __u32 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */61static const __u32 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 362 / (BICTCP_BETA_SCALE - beta);63/* calculate the "K" for (wmax-cwnd) = c/rtt * K^364 * so K = cubic_root( (wmax-cwnd)*rtt/c )65 * the unit of K is bictcp_HZ=2^10, not HZ66 *67 * c = bic_scale >> 1068 * rtt = 100ms69 *70 * the following code has been designed and tested for71 * cwnd < 1 million packets72 * RTT < 100 seconds73 * HZ < 1,000,00 (corresponding to 10 nano-second)74 */75 76/* 1/c * 2^2*bictcp_HZ * srtt, 2^40 */77static const __u64 cube_factor = (__u64)(1ull << (10+3*BICTCP_HZ))78 / (bic_scale * 10);79 80/* BIC TCP Parameters */81struct 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 point88 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 102static 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 117extern unsigned long CONFIG_HZ __kconfig;118#define HZ CONFIG_HZ119#define USEC_PER_MSEC 1000UL120#define USEC_PER_SEC 1000000UL121#define USEC_PER_JIFFY (USEC_PER_SEC / HZ)122 123static __u64 div64_u64(__u64 dividend, __u64 divisor)124{125 return dividend / divisor;126}127 128#define div64_ul div64_u64129 130#define BITS_PER_U64 (sizeof(__u64) * 8)131static 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 164static __u32 bictcp_clock_us(const struct sock *sk)165{166 return tcp_sk(sk)->tcp_mstamp;167}168 169static 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 180SEC("struct_ops")181void 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 194SEC("struct_ops")195void 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 Tarreau219 *220 * For x in [0..63],221 * v = cbrt(x << 18) - 1222 * cbrt(x) = (v[x] + 10) >> 6223 */224static 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 one236 * Newton-Raphson iteration.237 * Avg err ~= 0.195%238 */239static __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 iteration260 * 2261 * x = ( 2 * x + a / x ) / 3262 * k+1 k k263 */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 */272static 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 on303 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)304 */305 ca->bic_K = cubic_root(cube_factor306 * (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^3314 * (so time^3 is done by using 64 bit)315 * and without the support of division of 64bit numbers316 * (so all divisions are done by using 32 bit)317 * also NOTE the unit of those variables318 * time = (t - K) / 2^bictcp_HZ319 * c = bic_scale >> 10320 * rtt = (srtt >> 3) / HZ321 * !!! 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 else334 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 conservative352 * 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 357tcp_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 per380 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.381 */382 ca->cnt = max(ca->cnt, 2U);383}384 385SEC("struct_ops")386void 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 405SEC("struct_ops")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 else418 ca->last_max_cwnd = tp->snd_cwnd;419 420 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);421}422 423SEC("struct_ops")424void 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 65536433 434/* Account for TSO/GRO delays.435 * Otherwise short RTT flows could get too small ssthresh, since during436 * slow start we begin with small TSO packets and ca->delay_min would437 * 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 one439 * 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 */443static __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 454static 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 past470 * ca->delay_min/2.471 * Pacing might have delayed packets up to RTT/2472 * 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 500int bpf_cubic_acked_called = 0;501 502SEC("struct_ops")503void 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 532extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;533 534SEC("struct_ops")535__u32 BPF_PROG(bpf_cubic_undo_cwnd, struct sock *sk)536{537 return tcp_reno_undo_cwnd(sk);538}539 540SEC(".struct_ops")541struct 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