--- /dev/null
+// 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",
+};
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