/* * 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); } } /* * 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");