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+/*
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.2
+ * Home page:
+ * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
+ * This is from the implementation of CUBIC TCP in
+ * Injong Rhee, Lisong Xu.
+ * "CUBIC: A New TCP-Friendly High-Speed TCP Variant
+ * in PFLDnet 2005
+ * Available from:
+ * http://netsrv.csc.ncsu.edu/export/cubic-paper.pdf
+ *
+ * Unless CUBIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/math64.h>
+#include <net/tcp.h>
+
+#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
+ * max_cwnd = snd_cwnd * beta
+ */
+#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
+
+static int fast_convergence __read_mostly = 1;
+static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
+static int initial_ssthresh __read_mostly;
+static int bic_scale __read_mostly = 41;
+static int tcp_friendliness __read_mostly = 1;
+
+static u32 cube_rtt_scale __read_mostly;
+static u32 beta_scale __read_mostly;
+static u64 cube_factor __read_mostly;
+
+/* Note parameters that are used for precomputing scale factors are read-only */
+module_param(fast_convergence, int, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(bic_scale, int, 0444);
+MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
+module_param(tcp_friendliness, int, 0644);
+MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
+
+/* BIC TCP Parameters */
+struct bictcp {
+ u32 cnt; /* increase cwnd by 1 after ACKs */
+ u32 last_max_cwnd; /* last maximum snd_cwnd */
+ u32 loss_cwnd; /* congestion window at last loss */
+ 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 */
+ u32 epoch_start; /* beginning of an epoch */
+ u32 ack_cnt; /* number of acks */
+ u32 tcp_cwnd; /* estimated tcp cwnd */
+#define ACK_RATIO_SHIFT 4
+ u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
+};
+
+static inline void bictcp_reset(struct bictcp *ca)
+{
+ ca->cnt = 0;
+ ca->last_max_cwnd = 0;
+ ca->loss_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->delayed_ack = 2 << ACK_RATIO_SHIFT;
+ ca->ack_cnt = 0;
+ ca->tcp_cwnd = 0;
+}
+
+static void bictcp_init(struct sock *sk)
+{
+ bictcp_reset(inet_csk_ca(sk));
+ if (initial_ssthresh)
+ tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
+}
+
+/* calculate the cubic root of x using a table lookup followed by one
+ * Newton-Raphson iteration.
+ * Avg err ~= 0.195%
+ */
+static u32 cubic_root(u64 a)
+{
+ u32 x, b, shift;
+ /*
+ * 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,
+ };
+
+ b = fls64(a);
+ if (b < 7) {
+ /* a in [0..63] */
+ return ((u32)v[(u32)a] + 35) >> 6;
+ }
+
+ b = ((b * 84) >> 8) - 1;
+ shift = (a >> (b * 3));
+
+ 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 inline void bictcp_update(struct bictcp *ca, u32 cwnd)
+{
+ u64 offs;
+ u32 delta, t, bic_target, max_cnt;
+
+ ca->ack_cnt++; /* count the number of ACKs */
+
+ if (ca->last_cwnd == cwnd &&
+ (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
+ return;
+
+ ca->last_cwnd = cwnd;
+ ca->last_time = tcp_time_stamp;
+
+ if (ca->epoch_start == 0) {
+ ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
+ ca->ack_cnt = 1; /* 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 !!!
+ */
+
+ /* change the unit from HZ to bictcp_HZ */
+ t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
+ << BICTCP_HZ) / HZ;
+
+ 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*/
+ }
+
+ /* TCP Friendly */
+ if (tcp_friendliness) {
+ u32 scale = beta_scale;
+ delta = (cwnd * scale) >> 3;
+ while (ca->ack_cnt > delta) { /* update tcp cwnd */
+ ca->ack_cnt -= delta;
+ ca->tcp_cwnd++;
+ }
+
+ 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;
+ }
+ }
+
+ ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
+ if (ca->cnt == 0) /* cannot be zero */
+ ca->cnt = 1;
+}
+
+static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ if (!tcp_is_cwnd_limited(sk, in_flight))
+ return;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh)
+ tcp_slow_start(tp);
+ else {
+ bictcp_update(ca, tp->snd_cwnd);
+
+ /* In dangerous area, increase slowly.
+ * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
+ */
+ if (tp->snd_cwnd_cnt >= ca->cnt) {
+ if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+ tp->snd_cwnd++;
+ tp->snd_cwnd_cnt = 0;
+ } else
+ tp->snd_cwnd_cnt++;
+ }
+
+}
+
+static u32 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;
+
+ ca->loss_cwnd = tp->snd_cwnd;
+
+ return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+static u32 bictcp_undo_cwnd(struct sock *sk)
+{
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
+}
+
+static void bictcp_state(struct sock *sk, u8 new_state)
+{
+ if (new_state == TCP_CA_Loss)
+ bictcp_reset(inet_csk_ca(sk));
+}
+
+/* Track delayed acknowledgment ratio using sliding window
+ * ratio = (15*ratio + sample) / 16
+ */
+static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+ u32 delay;
+
+ if (icsk->icsk_ca_state == TCP_CA_Open) {
+ cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+ ca->delayed_ack += cnt;
+ }
+
+ /* Some calls are for duplicates without timetamps */
+ if (rtt_us < 0)
+ return;
+
+ /* Discard delay samples right after fast recovery */
+ if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
+ return;
+
+ delay = usecs_to_jiffies(rtt_us) << 3;
+ 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;
+}
+
+static struct tcp_congestion_ops cubictcp = {
+ .init = bictcp_init,
+ .ssthresh = bictcp_recalc_ssthresh,
+ .cong_avoid = bictcp_cong_avoid,
+ .set_state = bictcp_state,
+ .undo_cwnd = bictcp_undo_cwnd,
+ .pkts_acked = bictcp_acked,
+ .owner = THIS_MODULE,
+ .name = "cubic",
+};
+
+static int __init cubictcp_register(void)
+{
+ BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
+
+ /* Precompute a bunch of the scaling factors that are used per-packet
+ * based on SRTT of 100ms
+ */
+
+ beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
+
+ cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
+
+ /* 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 */
+ cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
+
+ /* divide by bic_scale and by constant Srtt (100ms) */
+ do_div(cube_factor, bic_scale * 10);
+
+ return tcp_register_congestion_control(&cubictcp);
+}
+
+static void __exit cubictcp_unregister(void)
+{
+ tcp_unregister_congestion_control(&cubictcp);
+}
+
+module_init(cubictcp_register);
+module_exit(cubictcp_unregister);
+
+MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CUBIC TCP");
+MODULE_VERSION("2.2");
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