net/ipv4/tcp_bic.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Binary Increase Congestion control for TCP
   4  * Home page:
   5  *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
   6  * This is from the implementation of BICTCP in
   7  * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
   8  *  "Binary Increase Congestion Control for Fast, Long Distance
   9  *  Networks" in InfoComm 2004
  10  * Available from:
  11  *  http://netsrv.csc.ncsu.edu/export/bitcp.pdf
  12  *
  13  * Unless BIC is enabled and congestion window is large
  14  * this behaves the same as the original Reno.
  15  */
  16
  17 #include <linux/mm.h>
  18 #include <linux/module.h>
  19 #include <net/tcp.h>
  20
  21 #define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
  22                                          * max_cwnd = snd_cwnd * beta
  23                                          */
  24 #define BICTCP_B                4        /*
  25                                           * In binary search,
  26                                           * go to point (max+min)/N
  27                                           */
  28
  29 static int fast_convergence = 1;
  30 static int max_increment = 16;
  31 static int low_window = 14;
  32 static int beta = 819;          /* = 819/1024 (BICTCP_BETA_SCALE) */
  33 static int initial_ssthresh;
  34 static int smooth_part = 20;
  35
  36 module_param(fast_convergence, int, 0644);
  37 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
  38 module_param(max_increment, int, 0644);
  39 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
  40 module_param(low_window, int, 0644);
  41 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
  42 module_param(beta, int, 0644);
  43 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
  44 module_param(initial_ssthresh, int, 0644);
  45 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
  46 module_param(smooth_part, int, 0644);
  47 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
  48
  49 /* BIC TCP Parameters */
  50 struct bictcp {
  51         u32     cnt;            /* increase cwnd by 1 after ACKs */
  52         u32     last_max_cwnd;  /* last maximum snd_cwnd */
  53         u32     last_cwnd;      /* the last snd_cwnd */
  54         u32     last_time;      /* time when updated last_cwnd */
  55         u32     epoch_start;    /* beginning of an epoch */
  56 #define ACK_RATIO_SHIFT 4
  57         u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
  58 };
  59
  60 static inline void bictcp_reset(struct bictcp *ca)
  61 {
  62         ca->cnt = 0;
  63         ca->last_max_cwnd = 0;
  64         ca->last_cwnd = 0;
  65         ca->last_time = 0;
  66         ca->epoch_start = 0;
  67         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
  68 }
  69
  70 static void bictcp_init(struct sock *sk)
  71 {
  72         struct bictcp *ca = inet_csk_ca(sk);
  73
  74         bictcp_reset(ca);
  75
  76         if (initial_ssthresh)
  77                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
  78 }
  79
  80 /*
  81  * Compute congestion window to use.
  82  */
  83 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
  84 {
  85         if (ca->last_cwnd == cwnd &&
  86             (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
  87                 return;
  88
  89         ca->last_cwnd = cwnd;
  90         ca->last_time = tcp_jiffies32;
  91
  92         if (ca->epoch_start == 0) /* record the beginning of an epoch */
  93                 ca->epoch_start = tcp_jiffies32;
  94
  95         /* start off normal */
  96         if (cwnd <= low_window) {
  97                 ca->cnt = cwnd;
  98                 return;
  99         }
 100
 101         /* binary increase */
 102         if (cwnd < ca->last_max_cwnd) {
 103                 __u32   dist = (ca->last_max_cwnd - cwnd)
 104                         / BICTCP_B;
 105
 106                 if (dist > max_increment)
 107                         /* linear increase */
 108                         ca->cnt = cwnd / max_increment;
 109                 else if (dist <= 1U)
 110                         /* binary search increase */
 111                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 112                 else
 113                         /* binary search increase */
 114                         ca->cnt = cwnd / dist;
 115         } else {
 116                 /* slow start AMD linear increase */
 117                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
 118                         /* slow start */
 119                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 120                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 121                         /* slow start */
 122                         ca->cnt = (cwnd * (BICTCP_B-1))
 123                                 / (cwnd - ca->last_max_cwnd);
 124                 else
 125                         /* linear increase */
 126                         ca->cnt = cwnd / max_increment;
 127         }
 128
 129         /* if in slow start or link utilization is very low */
 130         if (ca->last_max_cwnd == 0) {
 131                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 132                         ca->cnt = 20;
 133         }
 134
 135         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 136         if (ca->cnt == 0)                       /* cannot be zero */
 137                 ca->cnt = 1;
 138 }
 139
 140 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 141 {
 142         struct tcp_sock *tp = tcp_sk(sk);
 143         struct bictcp *ca = inet_csk_ca(sk);
 144
 145         if (!tcp_is_cwnd_limited(sk))
 146                 return;
 147
 148         if (tcp_in_slow_start(tp)) {
 149                 acked = tcp_slow_start(tp, acked);
 150                 if (!acked)
 151                         return;
 152         }
 153         bictcp_update(ca, tcp_snd_cwnd(tp));
 154         tcp_cong_avoid_ai(tp, ca->cnt, acked);
 155 }
 156
 157 /*
 158  *      behave like Reno until low_window is reached,
 159  *      then increase congestion window slowly
 160  */
 161 static u32 bictcp_recalc_ssthresh(struct sock *sk)
 162 {
 163         const struct tcp_sock *tp = tcp_sk(sk);
 164         struct bictcp *ca = inet_csk_ca(sk);
 165
 166         ca->epoch_start = 0;    /* end of epoch */
 167
 168         /* Wmax and fast convergence */
 169         if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
 170                 ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
 171                         / (2 * BICTCP_BETA_SCALE);
 172         else
 173                 ca->last_max_cwnd = tcp_snd_cwnd(tp);
 174
 175         if (tcp_snd_cwnd(tp) <= low_window)
 176                 return max(tcp_snd_cwnd(tp) >> 1U, 2U);
 177         else
 178                 return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
 179 }
 180
 181 static void bictcp_state(struct sock *sk, u8 new_state)
 182 {
 183         if (new_state == TCP_CA_Loss)
 184                 bictcp_reset(inet_csk_ca(sk));
 185 }
 186
 187 /* Track delayed acknowledgment ratio using sliding window
 188  * ratio = (15*ratio + sample) / 16
 189  */
 190 static void bictcp_acked(struct sock *sk, const struct ack_sample *sample)
 191 {
 192         const struct inet_connection_sock *icsk = inet_csk(sk);
 193
 194         if (icsk->icsk_ca_state == TCP_CA_Open) {
 195                 struct bictcp *ca = inet_csk_ca(sk);
 196
 197                 ca->delayed_ack += sample->pkts_acked -
 198                         (ca->delayed_ack >> ACK_RATIO_SHIFT);
 199         }
 200 }
 201
 202 static struct tcp_congestion_ops bictcp __read_mostly = {
 203         .init           = bictcp_init,
 204         .ssthresh       = bictcp_recalc_ssthresh,
 205         .cong_avoid     = bictcp_cong_avoid,
 206         .set_state      = bictcp_state,
 207         .undo_cwnd      = tcp_reno_undo_cwnd,
 208         .pkts_acked     = bictcp_acked,
 209         .owner          = THIS_MODULE,
 210         .name           = "bic",
 211 };
 212
 213 static int __init bictcp_register(void)
 214 {
 215         BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 216         return tcp_register_congestion_control(&bictcp);
 217 }
 218
 219 static void __exit bictcp_unregister(void)
 220 {
 221         tcp_unregister_congestion_control(&bictcp);
 222 }
 223
 224 module_init(bictcp_register);
 225 module_exit(bictcp_unregister);
 226
 227 MODULE_AUTHOR("Stephen Hemminger");
 228 MODULE_LICENSE("GPL");
 229 MODULE_DESCRIPTION("BIC TCP");