| // SPDX-License-Identifier: GPL-2.0-only |
| |
| /* WARNING: This implemenation is not necessarily the same |
| * as the tcp_cubic.c. The purpose is mainly for testing |
| * the kernel BPF logic. |
| * |
| * Highlights: |
| * 1. CONFIG_HZ .kconfig map is used. |
| * 2. In bictcp_update(), calculation is changed to use usec |
| * resolution (i.e. USEC_PER_JIFFY) instead of using jiffies. |
| * Thus, usecs_to_jiffies() is not used in the bpf_cubic.c. |
| * 3. In bitctcp_update() [under tcp_friendliness], the original |
| * "while (ca->ack_cnt > delta)" loop is changed to the equivalent |
| * "ca->ack_cnt / delta" operation. |
| */ |
| |
| #include <linux/bpf.h> |
| #include "bpf_tcp_helpers.h" |
| |
| char _license[] SEC("license") = "GPL"; |
| |
| #define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi) |
| |
| #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation |
| * max_cwnd = snd_cwnd * beta |
| */ |
| #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ |
| |
| /* Two methods of hybrid slow start */ |
| #define HYSTART_ACK_TRAIN 0x1 |
| #define HYSTART_DELAY 0x2 |
| |
| /* Number of delay samples for detecting the increase of delay */ |
| #define HYSTART_MIN_SAMPLES 8 |
| #define HYSTART_DELAY_MIN (4000U) /* 4ms */ |
| #define HYSTART_DELAY_MAX (16000U) /* 16 ms */ |
| #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX) |
| |
| static int fast_convergence = 1; |
| static const int beta = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */ |
| static int initial_ssthresh; |
| static const int bic_scale = 41; |
| static int tcp_friendliness = 1; |
| |
| static int hystart = 1; |
| static int hystart_detect = HYSTART_ACK_TRAIN | HYSTART_DELAY; |
| static int hystart_low_window = 16; |
| static int hystart_ack_delta_us = 2000; |
| |
| static const __u32 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |
| static const __u32 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3 |
| / (BICTCP_BETA_SCALE - beta); |
| /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 |
| * so K = cubic_root( (wmax-cwnd)*rtt/c ) |
| * the unit of K is bictcp_HZ=2^10, not HZ |
| * |
| * c = bic_scale >> 10 |
| * rtt = 100ms |
| * |
| * the following code has been designed and tested for |
| * cwnd < 1 million packets |
| * RTT < 100 seconds |
| * HZ < 1,000,00 (corresponding to 10 nano-second) |
| */ |
| |
| /* 1/c * 2^2*bictcp_HZ * srtt, 2^40 */ |
| static const __u64 cube_factor = (__u64)(1ull << (10+3*BICTCP_HZ)) |
| / (bic_scale * 10); |
| |
| /* BIC TCP Parameters */ |
| struct bictcp { |
| __u32 cnt; /* increase cwnd by 1 after ACKs */ |
| __u32 last_max_cwnd; /* last maximum snd_cwnd */ |
| __u32 last_cwnd; /* the last snd_cwnd */ |
| __u32 last_time; /* time when updated last_cwnd */ |
| __u32 bic_origin_point;/* origin point of bic function */ |
| __u32 bic_K; /* time to origin point |
| from the beginning of the current epoch */ |
| __u32 delay_min; /* min delay (usec) */ |
| __u32 epoch_start; /* beginning of an epoch */ |
| __u32 ack_cnt; /* number of acks */ |
| __u32 tcp_cwnd; /* estimated tcp cwnd */ |
| __u16 unused; |
| __u8 sample_cnt; /* number of samples to decide curr_rtt */ |
| __u8 found; /* the exit point is found? */ |
| __u32 round_start; /* beginning of each round */ |
| __u32 end_seq; /* end_seq of the round */ |
| __u32 last_ack; /* last time when the ACK spacing is close */ |
| __u32 curr_rtt; /* the minimum rtt of current round */ |
| }; |
| |
| static inline void bictcp_reset(struct bictcp *ca) |
| { |
| ca->cnt = 0; |
| ca->last_max_cwnd = 0; |
| ca->last_cwnd = 0; |
| ca->last_time = 0; |
| ca->bic_origin_point = 0; |
| ca->bic_K = 0; |
| ca->delay_min = 0; |
| ca->epoch_start = 0; |
| ca->ack_cnt = 0; |
| ca->tcp_cwnd = 0; |
| ca->found = 0; |
| } |
| |
| extern unsigned long CONFIG_HZ __kconfig; |
| #define HZ CONFIG_HZ |
| #define USEC_PER_MSEC 1000UL |
| #define USEC_PER_SEC 1000000UL |
| #define USEC_PER_JIFFY (USEC_PER_SEC / HZ) |
| |
| static __always_inline __u64 div64_u64(__u64 dividend, __u64 divisor) |
| { |
| return dividend / divisor; |
| } |
| |
| #define div64_ul div64_u64 |
| |
| #define BITS_PER_U64 (sizeof(__u64) * 8) |
| static __always_inline int fls64(__u64 x) |
| { |
| int num = BITS_PER_U64 - 1; |
| |
| if (x == 0) |
| return 0; |
| |
| if (!(x & (~0ull << (BITS_PER_U64-32)))) { |
| num -= 32; |
| x <<= 32; |
| } |
| if (!(x & (~0ull << (BITS_PER_U64-16)))) { |
| num -= 16; |
| x <<= 16; |
| } |
| if (!(x & (~0ull << (BITS_PER_U64-8)))) { |
| num -= 8; |
| x <<= 8; |
| } |
| if (!(x & (~0ull << (BITS_PER_U64-4)))) { |
| num -= 4; |
| x <<= 4; |
| } |
| if (!(x & (~0ull << (BITS_PER_U64-2)))) { |
| num -= 2; |
| x <<= 2; |
| } |
| if (!(x & (~0ull << (BITS_PER_U64-1)))) |
| num -= 1; |
| |
| return num + 1; |
| } |
| |
| static __always_inline __u32 bictcp_clock_us(const struct sock *sk) |
| { |
| return tcp_sk(sk)->tcp_mstamp; |
| } |
| |
| static __always_inline void bictcp_hystart_reset(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| ca->round_start = ca->last_ack = bictcp_clock_us(sk); |
| ca->end_seq = tp->snd_nxt; |
| ca->curr_rtt = ~0U; |
| ca->sample_cnt = 0; |
| } |
| |
| /* "struct_ops/" prefix is not a requirement |
| * It will be recognized as BPF_PROG_TYPE_STRUCT_OPS |
| * as long as it is used in one of the func ptr |
| * under SEC(".struct_ops"). |
| */ |
| SEC("struct_ops/bictcp_init") |
| void BPF_PROG(bictcp_init, struct sock *sk) |
| { |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| bictcp_reset(ca); |
| |
| if (hystart) |
| bictcp_hystart_reset(sk); |
| |
| if (!hystart && initial_ssthresh) |
| tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
| } |
| |
| /* No prefix in SEC will also work. |
| * The remaining tcp-cubic functions have an easier way. |
| */ |
| SEC("no-sec-prefix-bictcp_cwnd_event") |
| void BPF_PROG(bictcp_cwnd_event, struct sock *sk, enum tcp_ca_event event) |
| { |
| if (event == CA_EVENT_TX_START) { |
| struct bictcp *ca = inet_csk_ca(sk); |
| __u32 now = tcp_jiffies32; |
| __s32 delta; |
| |
| delta = now - tcp_sk(sk)->lsndtime; |
| |
| /* We were application limited (idle) for a while. |
| * Shift epoch_start to keep cwnd growth to cubic curve. |
| */ |
| if (ca->epoch_start && delta > 0) { |
| ca->epoch_start += delta; |
| if (after(ca->epoch_start, now)) |
| ca->epoch_start = now; |
| } |
| return; |
| } |
| } |
| |
| /* |
| * cbrt(x) MSB values for x MSB values in [0..63]. |
| * Precomputed then refined by hand - Willy Tarreau |
| * |
| * For x in [0..63], |
| * v = cbrt(x << 18) - 1 |
| * cbrt(x) = (v[x] + 10) >> 6 |
| */ |
| static const __u8 v[] = { |
| /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, |
| /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, |
| /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, |
| /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, |
| /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, |
| /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, |
| /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, |
| /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, |
| }; |
| |
| /* calculate the cubic root of x using a table lookup followed by one |
| * Newton-Raphson iteration. |
| * Avg err ~= 0.195% |
| */ |
| static __always_inline __u32 cubic_root(__u64 a) |
| { |
| __u32 x, b, shift; |
| |
| if (a < 64) { |
| /* a in [0..63] */ |
| return ((__u32)v[(__u32)a] + 35) >> 6; |
| } |
| |
| b = fls64(a); |
| b = ((b * 84) >> 8) - 1; |
| shift = (a >> (b * 3)); |
| |
| /* it is needed for verifier's bound check on v */ |
| if (shift >= 64) |
| return 0; |
| |
| x = ((__u32)(((__u32)v[shift] + 10) << b)) >> 6; |
| |
| /* |
| * Newton-Raphson iteration |
| * 2 |
| * x = ( 2 * x + a / x ) / 3 |
| * k+1 k k |
| */ |
| x = (2 * x + (__u32)div64_u64(a, (__u64)x * (__u64)(x - 1))); |
| x = ((x * 341) >> 10); |
| return x; |
| } |
| |
| /* |
| * Compute congestion window to use. |
| */ |
| static __always_inline void bictcp_update(struct bictcp *ca, __u32 cwnd, |
| __u32 acked) |
| { |
| __u32 delta, bic_target, max_cnt; |
| __u64 offs, t; |
| |
| ca->ack_cnt += acked; /* count the number of ACKed packets */ |
| |
| if (ca->last_cwnd == cwnd && |
| (__s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) |
| return; |
| |
| /* The CUBIC function can update ca->cnt at most once per jiffy. |
| * On all cwnd reduction events, ca->epoch_start is set to 0, |
| * which will force a recalculation of ca->cnt. |
| */ |
| if (ca->epoch_start && tcp_jiffies32 == ca->last_time) |
| goto tcp_friendliness; |
| |
| ca->last_cwnd = cwnd; |
| ca->last_time = tcp_jiffies32; |
| |
| if (ca->epoch_start == 0) { |
| ca->epoch_start = tcp_jiffies32; /* record beginning */ |
| ca->ack_cnt = acked; /* start counting */ |
| ca->tcp_cwnd = cwnd; /* syn with cubic */ |
| |
| if (ca->last_max_cwnd <= cwnd) { |
| ca->bic_K = 0; |
| ca->bic_origin_point = cwnd; |
| } else { |
| /* Compute new K based on |
| * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) |
| */ |
| ca->bic_K = cubic_root(cube_factor |
| * (ca->last_max_cwnd - cwnd)); |
| ca->bic_origin_point = ca->last_max_cwnd; |
| } |
| } |
| |
| /* cubic function - calc*/ |
| /* calculate c * time^3 / rtt, |
| * while considering overflow in calculation of time^3 |
| * (so time^3 is done by using 64 bit) |
| * and without the support of division of 64bit numbers |
| * (so all divisions are done by using 32 bit) |
| * also NOTE the unit of those veriables |
| * time = (t - K) / 2^bictcp_HZ |
| * c = bic_scale >> 10 |
| * rtt = (srtt >> 3) / HZ |
| * !!! The following code does not have overflow problems, |
| * if the cwnd < 1 million packets !!! |
| */ |
| |
| t = (__s32)(tcp_jiffies32 - ca->epoch_start) * USEC_PER_JIFFY; |
| t += ca->delay_min; |
| /* change the unit from usec to bictcp_HZ */ |
| t <<= BICTCP_HZ; |
| t /= USEC_PER_SEC; |
| |
| if (t < ca->bic_K) /* t - K */ |
| offs = ca->bic_K - t; |
| else |
| offs = t - ca->bic_K; |
| |
| /* c/rtt * (t-K)^3 */ |
| delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); |
| if (t < ca->bic_K) /* below origin*/ |
| bic_target = ca->bic_origin_point - delta; |
| else /* above origin*/ |
| bic_target = ca->bic_origin_point + delta; |
| |
| /* cubic function - calc bictcp_cnt*/ |
| if (bic_target > cwnd) { |
| ca->cnt = cwnd / (bic_target - cwnd); |
| } else { |
| ca->cnt = 100 * cwnd; /* very small increment*/ |
| } |
| |
| /* |
| * The initial growth of cubic function may be too conservative |
| * when the available bandwidth is still unknown. |
| */ |
| if (ca->last_max_cwnd == 0 && ca->cnt > 20) |
| ca->cnt = 20; /* increase cwnd 5% per RTT */ |
| |
| tcp_friendliness: |
| /* TCP Friendly */ |
| if (tcp_friendliness) { |
| __u32 scale = beta_scale; |
| __u32 n; |
| |
| /* update tcp cwnd */ |
| delta = (cwnd * scale) >> 3; |
| if (ca->ack_cnt > delta && delta) { |
| n = ca->ack_cnt / delta; |
| ca->ack_cnt -= n * delta; |
| ca->tcp_cwnd += n; |
| } |
| |
| if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */ |
| delta = ca->tcp_cwnd - cwnd; |
| max_cnt = cwnd / delta; |
| if (ca->cnt > max_cnt) |
| ca->cnt = max_cnt; |
| } |
| } |
| |
| /* The maximum rate of cwnd increase CUBIC allows is 1 packet per |
| * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT. |
| */ |
| ca->cnt = max(ca->cnt, 2U); |
| } |
| |
| /* Or simply use the BPF_STRUCT_OPS to avoid the SEC boiler plate. */ |
| void BPF_STRUCT_OPS(bictcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| if (!tcp_is_cwnd_limited(sk)) |
| return; |
| |
| if (tcp_in_slow_start(tp)) { |
| if (hystart && after(ack, ca->end_seq)) |
| bictcp_hystart_reset(sk); |
| acked = tcp_slow_start(tp, acked); |
| if (!acked) |
| return; |
| } |
| bictcp_update(ca, tp->snd_cwnd, acked); |
| tcp_cong_avoid_ai(tp, ca->cnt, acked); |
| } |
| |
| __u32 BPF_STRUCT_OPS(bictcp_recalc_ssthresh, struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| ca->epoch_start = 0; /* end of epoch */ |
| |
| /* Wmax and fast convergence */ |
| if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) |
| ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) |
| / (2 * BICTCP_BETA_SCALE); |
| else |
| ca->last_max_cwnd = tp->snd_cwnd; |
| |
| return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); |
| } |
| |
| void BPF_STRUCT_OPS(bictcp_state, struct sock *sk, __u8 new_state) |
| { |
| if (new_state == TCP_CA_Loss) { |
| bictcp_reset(inet_csk_ca(sk)); |
| bictcp_hystart_reset(sk); |
| } |
| } |
| |
| #define GSO_MAX_SIZE 65536 |
| |
| /* Account for TSO/GRO delays. |
| * Otherwise short RTT flows could get too small ssthresh, since during |
| * slow start we begin with small TSO packets and ca->delay_min would |
| * not account for long aggregation delay when TSO packets get bigger. |
| * Ideally even with a very small RTT we would like to have at least one |
| * TSO packet being sent and received by GRO, and another one in qdisc layer. |
| * We apply another 100% factor because @rate is doubled at this point. |
| * We cap the cushion to 1ms. |
| */ |
| static __always_inline __u32 hystart_ack_delay(struct sock *sk) |
| { |
| unsigned long rate; |
| |
| rate = sk->sk_pacing_rate; |
| if (!rate) |
| return 0; |
| return min((__u64)USEC_PER_MSEC, |
| div64_ul((__u64)GSO_MAX_SIZE * 4 * USEC_PER_SEC, rate)); |
| } |
| |
| static __always_inline void hystart_update(struct sock *sk, __u32 delay) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| __u32 threshold; |
| |
| if (hystart_detect & HYSTART_ACK_TRAIN) { |
| __u32 now = bictcp_clock_us(sk); |
| |
| /* first detection parameter - ack-train detection */ |
| if ((__s32)(now - ca->last_ack) <= hystart_ack_delta_us) { |
| ca->last_ack = now; |
| |
| threshold = ca->delay_min + hystart_ack_delay(sk); |
| |
| /* Hystart ack train triggers if we get ack past |
| * ca->delay_min/2. |
| * Pacing might have delayed packets up to RTT/2 |
| * during slow start. |
| */ |
| if (sk->sk_pacing_status == SK_PACING_NONE) |
| threshold >>= 1; |
| |
| if ((__s32)(now - ca->round_start) > threshold) { |
| ca->found = 1; |
| tp->snd_ssthresh = tp->snd_cwnd; |
| } |
| } |
| } |
| |
| if (hystart_detect & HYSTART_DELAY) { |
| /* obtain the minimum delay of more than sampling packets */ |
| if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { |
| if (ca->curr_rtt > delay) |
| ca->curr_rtt = delay; |
| |
| ca->sample_cnt++; |
| } else { |
| if (ca->curr_rtt > ca->delay_min + |
| HYSTART_DELAY_THRESH(ca->delay_min >> 3)) { |
| ca->found = 1; |
| tp->snd_ssthresh = tp->snd_cwnd; |
| } |
| } |
| } |
| } |
| |
| void BPF_STRUCT_OPS(bictcp_acked, struct sock *sk, |
| const struct ack_sample *sample) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| __u32 delay; |
| |
| /* Some calls are for duplicates without timetamps */ |
| if (sample->rtt_us < 0) |
| return; |
| |
| /* Discard delay samples right after fast recovery */ |
| if (ca->epoch_start && (__s32)(tcp_jiffies32 - ca->epoch_start) < HZ) |
| return; |
| |
| delay = sample->rtt_us; |
| if (delay == 0) |
| delay = 1; |
| |
| /* first time call or link delay decreases */ |
| if (ca->delay_min == 0 || ca->delay_min > delay) |
| ca->delay_min = delay; |
| |
| /* hystart triggers when cwnd is larger than some threshold */ |
| if (!ca->found && tcp_in_slow_start(tp) && hystart && |
| tp->snd_cwnd >= hystart_low_window) |
| hystart_update(sk, delay); |
| } |
| |
| __u32 BPF_STRUCT_OPS(tcp_reno_undo_cwnd, struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| |
| return max(tp->snd_cwnd, tp->prior_cwnd); |
| } |
| |
| SEC(".struct_ops") |
| struct tcp_congestion_ops cubic = { |
| .init = (void *)bictcp_init, |
| .ssthresh = (void *)bictcp_recalc_ssthresh, |
| .cong_avoid = (void *)bictcp_cong_avoid, |
| .set_state = (void *)bictcp_state, |
| .undo_cwnd = (void *)tcp_reno_undo_cwnd, |
| .cwnd_event = (void *)bictcp_cwnd_event, |
| .pkts_acked = (void *)bictcp_acked, |
| .name = "bpf_cubic", |
| }; |