--- /dev/null
+/*
+ * Binary Increase Congestion control for TCP
+ * Home page:
+ * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
+ * This is from the implementation of BICTCP in
+ * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
+ * "Binary Increase Congestion Control for Fast, Long Distance
+ * Networks" in InfoComm 2004
+ * Available from:
+ * http://netsrv.csc.ncsu.edu/export/bitcp.pdf
+ *
+ * Unless BIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
+ * max_cwnd = snd_cwnd * beta
+ */
+#define BICTCP_B 4 /*
+ * In binary search,
+ * go to point (max+min)/N
+ */
+
+static int fast_convergence = 1;
+static int max_increment = 16;
+static int low_window = 14;
+static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
+static int initial_ssthresh;
+static int smooth_part = 20;
+
+module_param(fast_convergence, int, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(max_increment, int, 0644);
+MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
+module_param(low_window, int, 0644);
+MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
+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(smooth_part, int, 0644);
+MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
+
+/* 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 epoch_start; /* beginning of an epoch */
+#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->last_cwnd = 0;
+ ca->last_time = 0;
+ ca->epoch_start = 0;
+ ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
+}
+
+static void bictcp_init(struct sock *sk)
+{
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ bictcp_reset(ca);
+ ca->loss_cwnd = 0;
+
+ if (initial_ssthresh)
+ tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
+}
+
+/*
+ * Compute congestion window to use.
+ */
+static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
+{
+ 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) /* record the beginning of an epoch */
+ ca->epoch_start = tcp_time_stamp;
+
+ /* start off normal */
+ if (cwnd <= low_window) {
+ ca->cnt = cwnd;
+ return;
+ }
+
+ /* binary increase */
+ if (cwnd < ca->last_max_cwnd) {
+ __u32 dist = (ca->last_max_cwnd - cwnd)
+ / BICTCP_B;
+
+ if (dist > max_increment)
+ /* linear increase */
+ ca->cnt = cwnd / max_increment;
+ else if (dist <= 1U)
+ /* binary search increase */
+ ca->cnt = (cwnd * smooth_part) / BICTCP_B;
+ else
+ /* binary search increase */
+ ca->cnt = cwnd / dist;
+ } else {
+ /* slow start AMD linear increase */
+ if (cwnd < ca->last_max_cwnd + BICTCP_B)
+ /* slow start */
+ ca->cnt = (cwnd * smooth_part) / BICTCP_B;
+ else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
+ /* slow start */
+ ca->cnt = (cwnd * (BICTCP_B-1))
+ / (cwnd - ca->last_max_cwnd);
+ else
+ /* linear increase */
+ ca->cnt = cwnd / max_increment;
+ }
+
+ /* if in slow start or link utilization is very low */
+ if (ca->last_max_cwnd == 0) {
+ if (ca->cnt > 20) /* increase cwnd 5% per RTT */
+ ca->cnt = 20;
+ }
+
+ 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 acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ if (!tcp_is_cwnd_limited(sk))
+ return;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh)
+ tcp_slow_start(tp, acked);
+ else {
+ bictcp_update(ca, tp->snd_cwnd);
+ tcp_cong_avoid_ai(tp, ca->cnt, 1);
+ }
+}
+
+/*
+ * behave like Reno until low_window is reached,
+ * then increase congestion window slowly
+ */
+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;
+
+ if (tp->snd_cwnd <= low_window)
+ return max(tp->snd_cwnd >> 1U, 2U);
+ else
+ return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+static u32 bictcp_undo_cwnd(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct bictcp *ca = inet_csk_ca(sk);
+
+ return max(tp->snd_cwnd, ca->loss_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)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (icsk->icsk_ca_state == TCP_CA_Open) {
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+ ca->delayed_ack += cnt;
+ }
+}
+
+static struct tcp_congestion_ops bictcp __read_mostly = {
+ .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 = "bic",
+};
+
+static int __init bictcp_register(void)
+{
+ BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
+ return tcp_register_congestion_control(&bictcp);
+}
+
+static void __exit bictcp_unregister(void)
+{
+ tcp_unregister_congestion_control(&bictcp);
+}
+
+module_init(bictcp_register);
+module_exit(bictcp_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("BIC TCP");
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