/* * TCP HYBLA * * TCP-HYBLA Congestion control algorithm, based on: * C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement * for Heterogeneous Networks", * International Journal on satellite Communications, * September 2004 * Daniele Lacamera * root at danielinux.net */ #include <linux/module.h> #include <net/tcp.h> /* Tcp Hybla structure. */ struct hybla { u8 hybla_en; u32 snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */ u32 rho; /* Rho parameter, integer part */ u32 rho2; /* Rho * Rho, integer part */ u32 rho_3ls; /* Rho parameter, <<3 */ u32 rho2_7ls; /* Rho^2, <<7 */ u32 minrtt; /* Minimum smoothed round trip time value seen */ }; /* Hybla reference round trip time (default= 1/40 sec = 25 ms), expressed in jiffies */ static int rtt0 = 25; module_param(rtt0, int, 0644); MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)"); /* This is called to refresh values for hybla parameters */ static inline void hybla_recalc_param (struct sock *sk) { struct hybla *ca = inet_csk_ca(sk); ca->rho_3ls = max_t(u32, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8); ca->rho = ca->rho_3ls >> 3; ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1; ca->rho2 = ca->rho2_7ls >>7; } static void hybla_init(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct hybla *ca = inet_csk_ca(sk); ca->rho = 0; ca->rho2 = 0; ca->rho_3ls = 0; ca->rho2_7ls = 0; ca->snd_cwnd_cents = 0; ca->hybla_en = 1; tp->snd_cwnd = 2; tp->snd_cwnd_clamp = 65535; /* 1st Rho measurement based on initial srtt */ hybla_recalc_param(sk); /* set minimum rtt as this is the 1st ever seen */ ca->minrtt = tp->srtt; tp->snd_cwnd = ca->rho; } static void hybla_state(struct sock *sk, u8 ca_state) { struct hybla *ca = inet_csk_ca(sk); ca->hybla_en = (ca_state == TCP_CA_Open); } static inline u32 hybla_fraction(u32 odds) { static const u32 fractions[] = { 128, 139, 152, 165, 181, 197, 215, 234, }; return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128; } /* TCP Hybla main routine. * This is the algorithm behavior: * o Recalc Hybla parameters if min_rtt has changed * o Give cwnd a new value based on the model proposed * o remember increments <1 */ static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 in_flight, int flag) { struct tcp_sock *tp = tcp_sk(sk); struct hybla *ca = inet_csk_ca(sk); u32 increment, odd, rho_fractions; int is_slowstart = 0; /* Recalculate rho only if this srtt is the lowest */ if (tp->srtt < ca->minrtt){ hybla_recalc_param(sk); ca->minrtt = tp->srtt; } if (!tcp_is_cwnd_limited(sk, in_flight)) return; if (!ca->hybla_en) return tcp_reno_cong_avoid(sk, ack, in_flight, flag); if (ca->rho == 0) hybla_recalc_param(sk); rho_fractions = ca->rho_3ls - (ca->rho << 3); if (tp->snd_cwnd < tp->snd_ssthresh) { /* * slow start * INC = 2^RHO - 1 * This is done by splitting the rho parameter * into 2 parts: an integer part and a fraction part. * Inrement<<7 is estimated by doing: * [2^(int+fract)]<<7 * that is equal to: * (2^int) * [(2^fract) <<7] * 2^int is straightly computed as 1<<int, * while we will use hybla_slowstart_fraction_increment() to * calculate 2^fract in a <<7 value. */ is_slowstart = 1; increment = ((1 << ca->rho) * hybla_fraction(rho_fractions)) - 128; } else { /* * congestion avoidance * INC = RHO^2 / W * as long as increment is estimated as (rho<<7)/window * it already is <<7 and we can easily count its fractions. */ increment = ca->rho2_7ls / tp->snd_cwnd; if (increment < 128) tp->snd_cwnd_cnt++; } odd = increment % 128; tp->snd_cwnd += increment >> 7; ca->snd_cwnd_cents += odd; /* check when fractions goes >=128 and increase cwnd by 1. */ while (ca->snd_cwnd_cents >= 128) { tp->snd_cwnd++; ca->snd_cwnd_cents -= 128; tp->snd_cwnd_cnt = 0; } /* clamp down slowstart cwnd to ssthresh value. */ if (is_slowstart) tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp); } static struct tcp_congestion_ops tcp_hybla = { .init = hybla_init, .ssthresh = tcp_reno_ssthresh, .min_cwnd = tcp_reno_min_cwnd, .cong_avoid = hybla_cong_avoid, .set_state = hybla_state, .owner = THIS_MODULE, .name = "hybla" }; static int __init hybla_register(void) { BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE); return tcp_register_congestion_control(&tcp_hybla); } static void __exit hybla_unregister(void) { tcp_unregister_congestion_control(&tcp_hybla); } module_init(hybla_register); module_exit(hybla_unregister); MODULE_AUTHOR("Daniele Lacamera"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("TCP Hybla");