net/ipv4/tcp_bic.c

   1 /*
   2  * Binary Increase Congestion control for TCP
   3  * Home page:
   4  *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
   5  * This is from the implementation of BICTCP in
   6  * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
   7  *  "Binary Increase Congestion Control for Fast, Long Distance
   8  *  Networks" in InfoComm 2004
   9  * Available from:
  10  *  http://netsrv.csc.ncsu.edu/export/bitcp.pdf
  11  *
  12  * Unless BIC is enabled and congestion window is large
  13  * this behaves the same as the original Reno.
  14  */
  15
  16 #include <linux/mm.h>
  17 #include <linux/module.h>
  18 #include <net/tcp.h>
  19
  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
  50 /* BIC TCP Parameters */
  51 struct bictcp {
  52         u32     cnt;            /* increase cwnd by 1 after ACKs */
  53         u32     last_max_cwnd;  /* last maximum snd_cwnd */
  54         u32     loss_cwnd;      /* congestion window at last loss */
  55         u32     last_cwnd;      /* the last snd_cwnd */
  56         u32     last_time;      /* time when updated last_cwnd */
  57         u32     epoch_start;    /* beginning of an epoch */
  58 #define ACK_RATIO_SHIFT 4
  59         u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
  60 };
  61
  62 static inline void bictcp_reset(struct bictcp *ca)
  63 {
  64         ca->cnt = 0;
  65         ca->last_max_cwnd = 0;
  66         ca->last_cwnd = 0;
  67         ca->last_time = 0;
  68         ca->epoch_start = 0;
  69         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
  70 }
  71
  72 static void bictcp_init(struct sock *sk)
  73 {
  74         struct bictcp *ca = inet_csk_ca(sk);
  75
  76         bictcp_reset(ca);
  77         ca->loss_cwnd = 0;
  78
  79         if (initial_ssthresh)
  80                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
  81 }
  82
  83 /*
  84  * Compute congestion window to use.
  85  */
  86 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
  87 {
  88         if (ca->last_cwnd == cwnd &&
  89             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
  90                 return;
  91
  92         ca->last_cwnd = cwnd;
  93         ca->last_time = tcp_time_stamp;
  94
  95         if (ca->epoch_start == 0) /* record the beginning of an epoch */
  96                 ca->epoch_start = tcp_time_stamp;
  97
  98         /* start off normal */
  99         if (cwnd <= low_window) {
 100                 ca->cnt = cwnd;
 101                 return;
 102         }
 103
 104         /* binary increase */
 105         if (cwnd < ca->last_max_cwnd) {
 106                 __u32   dist = (ca->last_max_cwnd - cwnd)
 107                         / BICTCP_B;
 108
 109                 if (dist > max_increment)
 110                         /* linear increase */
 111                         ca->cnt = cwnd / max_increment;
 112                 else if (dist <= 1U)
 113                         /* binary search increase */
 114                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 115                 else
 116                         /* binary search increase */
 117                         ca->cnt = cwnd / dist;
 118         } else {
 119                 /* slow start AMD linear increase */
 120                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
 121                         /* slow start */
 122                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 123                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 124                         /* slow start */
 125                         ca->cnt = (cwnd * (BICTCP_B-1))
 126                                 / (cwnd - ca->last_max_cwnd);
 127                 else
 128                         /* linear increase */
 129                         ca->cnt = cwnd / max_increment;
 130         }
 131
 132         /* if in slow start or link utilization is very low */
 133         if (ca->last_max_cwnd == 0) {
 134                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 135                         ca->cnt = 20;
 136         }
 137
 138         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 139         if (ca->cnt == 0)                       /* cannot be zero */
 140                 ca->cnt = 1;
 141 }
 142
 143 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked,
 144                               u32 in_flight)
 145 {
 146         struct tcp_sock *tp = tcp_sk(sk);
 147         struct bictcp *ca = inet_csk_ca(sk);
 148
 149         if (!tcp_is_cwnd_limited(sk, in_flight))
 150                 return;
 151
 152         if (tp->snd_cwnd <= tp->snd_ssthresh)
 153                 tcp_slow_start(tp, acked);
 154         else {
 155                 bictcp_update(ca, tp->snd_cwnd);
 156                 tcp_cong_avoid_ai(tp, ca->cnt);
 157         }
 158
 159 }
 160
 161 /*
 162  *      behave like Reno until low_window is reached,
 163  *      then increase congestion window slowly
 164  */
 165 static u32 bictcp_recalc_ssthresh(struct sock *sk)
 166 {
 167         const struct tcp_sock *tp = tcp_sk(sk);
 168         struct bictcp *ca = inet_csk_ca(sk);
 169
 170         ca->epoch_start = 0;    /* end of epoch */
 171
 172         /* Wmax and fast convergence */
 173         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 174                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 175                         / (2 * BICTCP_BETA_SCALE);
 176         else
 177                 ca->last_max_cwnd = tp->snd_cwnd;
 178
 179         ca->loss_cwnd = tp->snd_cwnd;
 180
 181
 182         if (tp->snd_cwnd <= low_window)
 183                 return max(tp->snd_cwnd >> 1U, 2U);
 184         else
 185                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 186 }
 187
 188 static u32 bictcp_undo_cwnd(struct sock *sk)
 189 {
 190         const struct tcp_sock *tp = tcp_sk(sk);
 191         const struct bictcp *ca = inet_csk_ca(sk);
 192         return max(tp->snd_cwnd, ca->loss_cwnd);
 193 }
 194
 195 static void bictcp_state(struct sock *sk, u8 new_state)
 196 {
 197         if (new_state == TCP_CA_Loss)
 198                 bictcp_reset(inet_csk_ca(sk));
 199 }
 200
 201 /* Track delayed acknowledgment ratio using sliding window
 202  * ratio = (15*ratio + sample) / 16
 203  */
 204 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
 205 {
 206         const struct inet_connection_sock *icsk = inet_csk(sk);
 207
 208         if (icsk->icsk_ca_state == TCP_CA_Open) {
 209                 struct bictcp *ca = inet_csk_ca(sk);
 210                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 211                 ca->delayed_ack += cnt;
 212         }
 213 }
 214
 215
 216 static struct tcp_congestion_ops bictcp __read_mostly = {
 217         .init           = bictcp_init,
 218         .ssthresh       = bictcp_recalc_ssthresh,
 219         .cong_avoid     = bictcp_cong_avoid,
 220         .set_state      = bictcp_state,
 221         .undo_cwnd      = bictcp_undo_cwnd,
 222         .pkts_acked     = bictcp_acked,
 223         .owner          = THIS_MODULE,
 224         .name           = "bic",
 225 };
 226
 227 static int __init bictcp_register(void)
 228 {
 229         BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 230         return tcp_register_congestion_control(&bictcp);
 231 }
 232
 233 static void __exit bictcp_unregister(void)
 234 {
 235         tcp_unregister_congestion_control(&bictcp);
 236 }
 237
 238 module_init(bictcp_register);
 239 module_exit(bictcp_unregister);
 240
 241 MODULE_AUTHOR("Stephen Hemminger");
 242 MODULE_LICENSE("GPL");
 243 MODULE_DESCRIPTION("BIC TCP");