net/ipv4/tcp_hybla.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * TCP HYBLA
0004  *
0005  * TCP-HYBLA Congestion control algorithm, based on:
0006  *   C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
0007  *   for Heterogeneous Networks",
0008  *   International Journal on satellite Communications,
0009  *                     September 2004
0010  *    Daniele Lacamera
0011  *    root at danielinux.net
0012  */
0013
0014 #include <linux/module.h>
0015 #include <net/tcp.h>
0016
0017 /* Tcp Hybla structure. */
0018 struct hybla {
0019     bool  hybla_en;
0020     u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
0021     u32   rho;        /* Rho parameter, integer part  */
0022     u32   rho2;       /* Rho * Rho, integer part */
0023     u32   rho_3ls;        /* Rho parameter, <<3 */
0024     u32   rho2_7ls;       /* Rho^2, <<7 */
0025     u32   minrtt_us;      /* Minimum smoothed round trip time value seen */
0026 };
0027
0028 /* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
0029 static int rtt0 = 25;
0030 module_param(rtt0, int, 0644);
0031 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
0032
0033 /* This is called to refresh values for hybla parameters */
0034 static inline void hybla_recalc_param (struct sock *sk)
0035 {
0036     struct hybla *ca = inet_csk_ca(sk);
0037
0038     ca->rho_3ls = max_t(u32,
0039                 tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
0040                 8U);
0041     ca->rho = ca->rho_3ls >> 3;
0042     ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
0043     ca->rho2 = ca->rho2_7ls >> 7;
0044 }
0045
0046 static void hybla_init(struct sock *sk)
0047 {
0048     struct tcp_sock *tp = tcp_sk(sk);
0049     struct hybla *ca = inet_csk_ca(sk);
0050
0051     ca->rho = 0;
0052     ca->rho2 = 0;
0053     ca->rho_3ls = 0;
0054     ca->rho2_7ls = 0;
0055     ca->snd_cwnd_cents = 0;
0056     ca->hybla_en = true;
0057     tcp_snd_cwnd_set(tp, 2);
0058     tp->snd_cwnd_clamp = 65535;
0059
0060     /* 1st Rho measurement based on initial srtt */
0061     hybla_recalc_param(sk);
0062
0063     /* set minimum rtt as this is the 1st ever seen */
0064     ca->minrtt_us = tp->srtt_us;
0065     tcp_snd_cwnd_set(tp, ca->rho);
0066 }
0067
0068 static void hybla_state(struct sock *sk, u8 ca_state)
0069 {
0070     struct hybla *ca = inet_csk_ca(sk);
0071
0072     ca->hybla_en = (ca_state == TCP_CA_Open);
0073 }
0074
0075 static inline u32 hybla_fraction(u32 odds)
0076 {
0077     static const u32 fractions[] = {
0078         128, 139, 152, 165, 181, 197, 215, 234,
0079     };
0080
0081     return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
0082 }
0083
0084 /* TCP Hybla main routine.
0085  * This is the algorithm behavior:
0086  *     o Recalc Hybla parameters if min_rtt has changed
0087  *     o Give cwnd a new value based on the model proposed
0088  *     o remember increments <1
0089  */
0090 static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
0091 {
0092     struct tcp_sock *tp = tcp_sk(sk);
0093     struct hybla *ca = inet_csk_ca(sk);
0094     u32 increment, odd, rho_fractions;
0095     int is_slowstart = 0;
0096
0097     /*  Recalculate rho only if this srtt is the lowest */
0098     if (tp->srtt_us < ca->minrtt_us) {
0099         hybla_recalc_param(sk);
0100         ca->minrtt_us = tp->srtt_us;
0101     }
0102
0103     if (!tcp_is_cwnd_limited(sk))
0104         return;
0105
0106     if (!ca->hybla_en) {
0107         tcp_reno_cong_avoid(sk, ack, acked);
0108         return;
0109     }
0110
0111     if (ca->rho == 0)
0112         hybla_recalc_param(sk);
0113
0114     rho_fractions = ca->rho_3ls - (ca->rho << 3);
0115
0116     if (tcp_in_slow_start(tp)) {
0117         /*
0118          * slow start
0119          *      INC = 2^RHO - 1
0120          * This is done by splitting the rho parameter
0121          * into 2 parts: an integer part and a fraction part.
0122          * Inrement<<7 is estimated by doing:
0123          *         [2^(int+fract)]<<7
0124          * that is equal to:
0125          *         (2^int)  *  [(2^fract) <<7]
0126          * 2^int is straightly computed as 1<<int,
0127          * while we will use hybla_slowstart_fraction_increment() to
0128          * calculate 2^fract in a <<7 value.
0129          */
0130         is_slowstart = 1;
0131         increment = ((1 << min(ca->rho, 16U)) *
0132             hybla_fraction(rho_fractions)) - 128;
0133     } else {
0134         /*
0135          * congestion avoidance
0136          * INC = RHO^2 / W
0137          * as long as increment is estimated as (rho<<7)/window
0138          * it already is <<7 and we can easily count its fractions.
0139          */
0140         increment = ca->rho2_7ls / tcp_snd_cwnd(tp);
0141         if (increment < 128)
0142             tp->snd_cwnd_cnt++;
0143     }
0144
0145     odd = increment % 128;
0146     tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + (increment >> 7));
0147     ca->snd_cwnd_cents += odd;
0148
0149     /* check when fractions goes >=128 and increase cwnd by 1. */
0150     while (ca->snd_cwnd_cents >= 128) {
0151         tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
0152         ca->snd_cwnd_cents -= 128;
0153         tp->snd_cwnd_cnt = 0;
0154     }
0155     /* check when cwnd has not been incremented for a while */
0156     if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
0157         tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
0158         tp->snd_cwnd_cnt = 0;
0159     }
0160     /* clamp down slowstart cwnd to ssthresh value. */
0161     if (is_slowstart)
0162         tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_ssthresh));
0163
0164     tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
0165 }
0166
0167 static struct tcp_congestion_ops tcp_hybla __read_mostly = {
0168     .init       = hybla_init,
0169     .ssthresh   = tcp_reno_ssthresh,
0170     .undo_cwnd  = tcp_reno_undo_cwnd,
0171     .cong_avoid = hybla_cong_avoid,
0172     .set_state  = hybla_state,
0173
0174     .owner      = THIS_MODULE,
0175     .name       = "hybla"
0176 };
0177
0178 static int __init hybla_register(void)
0179 {
0180     BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
0181     return tcp_register_congestion_control(&tcp_hybla);
0182 }
0183
0184 static void __exit hybla_unregister(void)
0185 {
0186     tcp_unregister_congestion_control(&tcp_hybla);
0187 }
0188
0189 module_init(hybla_register);
0190 module_exit(hybla_unregister);
0191
0192 MODULE_AUTHOR("Daniele Lacamera");
0193 MODULE_LICENSE("GPL");
0194 MODULE_DESCRIPTION("TCP Hybla");