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 #define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
  21                                          * max_cwnd = snd_cwnd * beta
  22                                          */
  23 #define BICTCP_B                4        /*
  24                                           * In binary search,
  25                                           * go to point (max+min)/N
  26                                           */
  27
  28 static int fast_convergence = 1;
  29 static int max_increment = 16;
  30 static int low_window = 14;
  31 static int beta = 819;          /* = 819/1024 (BICTCP_BETA_SCALE) */
  32 static int initial_ssthresh;
  33 static int smooth_part = 20;
  34
  35 module_param(fast_convergence, int, 0644);
  36 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
  37 module_param(max_increment, int, 0644);
  38 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
  39 module_param(low_window, int, 0644);
  40 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
  41 module_param(beta, int, 0644);
  42 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
  43 module_param(initial_ssthresh, int, 0644);
  44 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
  45 module_param(smooth_part, int, 0644);
  46 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
  47
  48 /* BIC TCP Parameters */
  49 struct bictcp {
  50         u32     cnt;            /* increase cwnd by 1 after ACKs */
  51         u32     last_max_cwnd;  /* last maximum snd_cwnd */
  52         u32     loss_cwnd;      /* congestion window at last loss */
  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         ca->loss_cwnd = 0;
  76
  77         if (initial_ssthresh)
  78                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
  79 }
  80
  81 /*
  82  * Compute congestion window to use.
  83  */
  84 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
  85 {
  86         if (ca->last_cwnd == cwnd &&
  87             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
  88                 return;
  89
  90         ca->last_cwnd = cwnd;
  91         ca->last_time = tcp_time_stamp;
  92
  93         if (ca->epoch_start == 0) /* record the beginning of an epoch */
  94                 ca->epoch_start = tcp_time_stamp;
  95
  96         /* start off normal */
  97         if (cwnd <= low_window) {
  98                 ca->cnt = cwnd;
  99                 return;
 100         }
 101
 102         /* binary increase */
 103         if (cwnd < ca->last_max_cwnd) {
 104                 __u32   dist = (ca->last_max_cwnd - cwnd)
 105                         / BICTCP_B;
 106
 107                 if (dist > max_increment)
 108                         /* linear increase */
 109                         ca->cnt = cwnd / max_increment;
 110                 else if (dist <= 1U)
 111                         /* binary search increase */
 112                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 113                 else
 114                         /* binary search increase */
 115                         ca->cnt = cwnd / dist;
 116         } else {
 117                 /* slow start AMD linear increase */
 118                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
 119                         /* slow start */
 120                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 121                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 122                         /* slow start */
 123                         ca->cnt = (cwnd * (BICTCP_B-1))
 124                                 / (cwnd - ca->last_max_cwnd);
 125                 else
 126                         /* linear increase */
 127                         ca->cnt = cwnd / max_increment;
 128         }
 129
 130         /* if in slow start or link utilization is very low */
 131         if (ca->last_max_cwnd == 0) {
 132                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 133                         ca->cnt = 20;
 134         }
 135
 136         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 137         if (ca->cnt == 0)                       /* cannot be zero */
 138                 ca->cnt = 1;
 139 }
 140
 141 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 142 {
 143         struct tcp_sock *tp = tcp_sk(sk);
 144         struct bictcp *ca = inet_csk_ca(sk);
 145
 146         if (!tcp_is_cwnd_limited(sk))
 147                 return;
 148
 149         if (tp->snd_cwnd <= tp->snd_ssthresh)
 150                 tcp_slow_start(tp, acked);
 151         else {
 152                 bictcp_update(ca, tp->snd_cwnd);
 153                 tcp_cong_avoid_ai(tp, ca->cnt, 1);
 154         }
 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 (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 170                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 171                         / (2 * BICTCP_BETA_SCALE);
 172         else
 173                 ca->last_max_cwnd = tp->snd_cwnd;
 174
 175         ca->loss_cwnd = tp->snd_cwnd;
 176
 177         if (tp->snd_cwnd <= low_window)
 178                 return max(tp->snd_cwnd >> 1U, 2U);
 179         else
 180                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 181 }
 182
 183 static u32 bictcp_undo_cwnd(struct sock *sk)
 184 {
 185         const struct tcp_sock *tp = tcp_sk(sk);
 186         const struct bictcp *ca = inet_csk_ca(sk);
 187
 188         return max(tp->snd_cwnd, ca->loss_cwnd);
 189 }
 190
 191 static void bictcp_state(struct sock *sk, u8 new_state)
 192 {
 193         if (new_state == TCP_CA_Loss)
 194                 bictcp_reset(inet_csk_ca(sk));
 195 }
 196
 197 /* Track delayed acknowledgment ratio using sliding window
 198  * ratio = (15*ratio + sample) / 16
 199  */
 200 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
 201 {
 202         const struct inet_connection_sock *icsk = inet_csk(sk);
 203
 204         if (icsk->icsk_ca_state == TCP_CA_Open) {
 205                 struct bictcp *ca = inet_csk_ca(sk);
 206
 207                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 208                 ca->delayed_ack += cnt;
 209         }
 210 }
 211
 212 static struct tcp_congestion_ops bictcp __read_mostly = {
 213         .init           = bictcp_init,
 214         .ssthresh       = bictcp_recalc_ssthresh,
 215         .cong_avoid     = bictcp_cong_avoid,
 216         .set_state      = bictcp_state,
 217         .undo_cwnd      = bictcp_undo_cwnd,
 218         .pkts_acked     = bictcp_acked,
 219         .owner          = THIS_MODULE,
 220         .name           = "bic",
 221 };
 222
 223 static int __init bictcp_register(void)
 224 {
 225         BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 226         return tcp_register_congestion_control(&bictcp);
 227 }
 228
 229 static void __exit bictcp_unregister(void)
 230 {
 231         tcp_unregister_congestion_control(&bictcp);
 232 }
 233
 234 module_init(bictcp_register);
 235 module_exit(bictcp_unregister);
 236
 237 MODULE_AUTHOR("Stephen Hemminger");
 238 MODULE_LICENSE("GPL");
 239 MODULE_DESCRIPTION("BIC TCP");