--- /dev/null
+/*
+ * Binary Increase Congestion control for TCP
+ *
+ * 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://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
+ *
+ * Unless BIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include <linux/config.h>
+#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 = 32;
+static int low_window = 14;
+static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
+static int low_utilization_threshold = 153;
+static int low_utilization_period = 2;
+static int initial_ssthresh = 100;
+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(low_utilization_threshold, int, 0644);
+MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
+module_param(low_utilization_period, int, 0644);
+MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
+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 delay_min; /* min delay */
+ u32 delay_max; /* max delay */
+ u32 last_delay;
+ u8 low_utilization;/* 0: high; 1: low */
+ u32 low_utilization_start; /* starting time of low utilization detection*/
+ 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->loss_cwnd = 0;
+ ca->last_cwnd = 0;
+ ca->last_time = 0;
+ ca->delay_min = 0;
+ ca->delay_max = 0;
+ ca->last_delay = 0;
+ ca->low_utilization = 0;
+ ca->low_utilization_start = 0;
+ ca->epoch_start = 0;
+ ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
+}
+
+static void bictcp_init(struct tcp_sock *tp)
+{
+ bictcp_reset(tcp_ca(tp));
+ if (initial_ssthresh)
+ tp->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->loss_cwnd == 0 ||
+ (cwnd > ca->loss_cwnd && ca->low_utilization)) {
+ 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;
+}
+
+
+/* Detect low utilization in congestion avoidance */
+static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
+{
+ struct bictcp *ca = tcp_ca(tp);
+ u32 dist, delay;
+
+ /* No time stamp */
+ if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
+ /* Discard delay samples right after fast recovery */
+ tcp_time_stamp < ca->epoch_start + HZ ||
+ /* this delay samples may not be accurate */
+ flag == 0) {
+ ca->last_delay = 0;
+ goto notlow;
+ }
+
+ delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/
+ ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
+ if (delay == 0) /* no previous delay sample */
+ goto notlow;
+
+ /* first time call or link delay decreases */
+ if (ca->delay_min == 0 || ca->delay_min > delay) {
+ ca->delay_min = ca->delay_max = delay;
+ goto notlow;
+ }
+
+ if (ca->delay_max < delay)
+ ca->delay_max = delay;
+
+ /* utilization is low, if avg delay < dist*threshold
+ for checking_period time */
+ dist = ca->delay_max - ca->delay_min;
+ if (dist <= ca->delay_min>>6 ||
+ tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10)
+ goto notlow;
+
+ if (ca->low_utilization_start == 0) {
+ ca->low_utilization = 0;
+ ca->low_utilization_start = tcp_time_stamp;
+ } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
+ > low_utilization_period*HZ) {
+ ca->low_utilization = 1;
+ }
+
+ return;
+
+ notlow:
+ ca->low_utilization = 0;
+ ca->low_utilization_start = 0;
+
+}
+
+static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
+ u32 seq_rtt, u32 in_flight, int data_acked)
+{
+ struct bictcp *ca = tcp_ca(tp);
+
+ bictcp_low_utilization(tp, data_acked);
+
+ if (in_flight < tp->snd_cwnd)
+ return;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh) {
+ /* In "safe" area, increase. */
+ if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+ tp->snd_cwnd++;
+ } 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++;
+ }
+
+}
+
+/*
+ * behave like Reno until low_window is reached,
+ * then increase congestion window slowly
+ */
+static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
+{
+ struct bictcp *ca = tcp_ca(tp);
+
+ ca->epoch_start = 0; /* end of epoch */
+
+ /* in case of wrong delay_max*/
+ if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
+ ca->delay_max = ca->delay_min
+ + ((ca->delay_max - ca->delay_min)* 90) / 100;
+
+ /* 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 tcp_sock *tp)
+{
+ struct bictcp *ca = tcp_ca(tp);
+
+ return max(tp->snd_cwnd, ca->last_max_cwnd);
+}
+
+static u32 bictcp_min_cwnd(struct tcp_sock *tp)
+{
+ return tp->snd_ssthresh;
+}
+
+static void bictcp_state(struct tcp_sock *tp, u8 new_state)
+{
+ if (new_state == TCP_CA_Loss)
+ bictcp_reset(tcp_ca(tp));
+}
+
+/* Track delayed acknowledgement ratio using sliding window
+ * ratio = (15*ratio + sample) / 16
+ */
+static void bictcp_acked(struct tcp_sock *tp, u32 cnt)
+{
+ if (cnt > 0 && tp->ca_state == TCP_CA_Open) {
+ struct bictcp *ca = tcp_ca(tp);
+ cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+ ca->delayed_ack += cnt;
+ }
+}
+
+
+static struct tcp_congestion_ops bictcp = {
+ .init = bictcp_init,
+ .ssthresh = bictcp_recalc_ssthresh,
+ .cong_avoid = bictcp_cong_avoid,
+ .set_state = bictcp_state,
+ .undo_cwnd = bictcp_undo_cwnd,
+ .min_cwnd = bictcp_min_cwnd,
+ .pkts_acked = bictcp_acked,
+ .owner = THIS_MODULE,
+ .name = "bic",
+};
+
+static int __init bictcp_register(void)
+{
+ BUG_ON(sizeof(struct bictcp) > TCP_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");
projects / linux-2.6 / commitdiff