/* * 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");