net/ipv4/tcp_bic.c

   1 /*
   2  * Binary Increase Congestion control for TCP
   3  *
   4  * This is from the implementation of BICTCP in
   5  * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
   6  *  "Binary Increase Congestion Control for Fast, Long Distance
   7  *  Networks" in InfoComm 2004
   8  * Available from:
   9  *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
  10  *
  11  * Unless BIC is enabled and congestion window is large
  12  * this behaves the same as the original Reno.
  13  */
  14
  15 #include <linux/config.h>
  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 = 32;
  31 static int low_window = 14;
  32 static int beta = 819;          /* = 819/1024 (BICTCP_BETA_SCALE) */
  33 static int low_utilization_threshold = 153;
  34 static int low_utilization_period = 2;
  35 static int initial_ssthresh = 100;
  36 static int smooth_part = 20;
  37
  38 module_param(fast_convergence, int, 0644);
  39 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
  40 module_param(max_increment, int, 0644);
  41 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
  42 module_param(low_window, int, 0644);
  43 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
  44 module_param(beta, int, 0644);
  45 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
  46 module_param(low_utilization_threshold, int, 0644);
  47 MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
  48 module_param(low_utilization_period, int, 0644);
  49 MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
  50 module_param(initial_ssthresh, int, 0644);
  51 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
  52 module_param(smooth_part, int, 0644);
  53 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
  54
  55
  56 /* BIC TCP Parameters */
  57 struct bictcp {
  58         u32     cnt;            /* increase cwnd by 1 after ACKs */
  59         u32     last_max_cwnd;  /* last maximum snd_cwnd */
  60         u32     loss_cwnd;      /* congestion window at last loss */
  61         u32     last_cwnd;      /* the last snd_cwnd */
  62         u32     last_time;      /* time when updated last_cwnd */
  63         u32     delay_min;      /* min delay */
  64         u32     delay_max;      /* max delay */
  65         u32     last_delay;
  66         u8      low_utilization;/* 0: high; 1: low */
  67         u32     low_utilization_start;  /* starting time of low utilization detection*/
  68         u32     epoch_start;    /* beginning of an epoch */
  69 #define ACK_RATIO_SHIFT 4
  70         u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
  71 };
  72
  73 static inline void bictcp_reset(struct bictcp *ca)
  74 {
  75         ca->cnt = 0;
  76         ca->last_max_cwnd = 0;
  77         ca->loss_cwnd = 0;
  78         ca->last_cwnd = 0;
  79         ca->last_time = 0;
  80         ca->delay_min = 0;
  81         ca->delay_max = 0;
  82         ca->last_delay = 0;
  83         ca->low_utilization = 0;
  84         ca->low_utilization_start = 0;
  85         ca->epoch_start = 0;
  86         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
  87 }
  88
  89 static void bictcp_init(struct sock *sk)
  90 {
  91         bictcp_reset(inet_csk_ca(sk));
  92         if (initial_ssthresh)
  93                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
  94 }
  95
  96 /*
  97  * Compute congestion window to use.
  98  */
  99 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 100 {
 101         if (ca->last_cwnd == cwnd &&
 102             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
 103                 return;
 104
 105         ca->last_cwnd = cwnd;
 106         ca->last_time = tcp_time_stamp;
 107
 108         if (ca->epoch_start == 0) /* record the beginning of an epoch */
 109                 ca->epoch_start = tcp_time_stamp;
 110
 111         /* start off normal */
 112         if (cwnd <= low_window) {
 113                 ca->cnt = cwnd;
 114                 return;
 115         }
 116
 117         /* binary increase */
 118         if (cwnd < ca->last_max_cwnd) {
 119                 __u32   dist = (ca->last_max_cwnd - cwnd)
 120                         / BICTCP_B;
 121
 122                 if (dist > max_increment)
 123                         /* linear increase */
 124                         ca->cnt = cwnd / max_increment;
 125                 else if (dist <= 1U)
 126                         /* binary search increase */
 127                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 128                 else
 129                         /* binary search increase */
 130                         ca->cnt = cwnd / dist;
 131         } else {
 132                 /* slow start AMD linear increase */
 133                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
 134                         /* slow start */
 135                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 136                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 137                         /* slow start */
 138                         ca->cnt = (cwnd * (BICTCP_B-1))
 139                                 / cwnd-ca->last_max_cwnd;
 140                 else
 141                         /* linear increase */
 142                         ca->cnt = cwnd / max_increment;
 143         }
 144
 145         /* if in slow start or link utilization is very low */
 146         if ( ca->loss_cwnd == 0 ||
 147              (cwnd > ca->loss_cwnd && ca->low_utilization)) {
 148                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 149                         ca->cnt = 20;
 150         }
 151
 152         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 153         if (ca->cnt == 0)                       /* cannot be zero */
 154                 ca->cnt = 1;
 155 }
 156
 157
 158 /* Detect low utilization in congestion avoidance */
 159 static inline void bictcp_low_utilization(struct sock *sk, int flag)
 160 {
 161         const struct tcp_sock *tp = tcp_sk(sk);
 162         struct bictcp *ca = inet_csk_ca(sk);
 163         u32 dist, delay;
 164
 165         /* No time stamp */
 166         if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
 167              /* Discard delay samples right after fast recovery */
 168              tcp_time_stamp < ca->epoch_start + HZ ||
 169              /* this delay samples may not be accurate */
 170              flag == 0) {
 171                 ca->last_delay = 0;
 172                 goto notlow;
 173         }
 174
 175         delay = ca->last_delay<<3;      /* use the same scale as tp->srtt*/
 176         ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
 177         if (delay == 0)                 /* no previous delay sample */
 178                 goto notlow;
 179
 180         /* first time call or link delay decreases */
 181         if (ca->delay_min == 0 || ca->delay_min > delay) {
 182                 ca->delay_min = ca->delay_max = delay;
 183                 goto notlow;
 184         }
 185
 186         if (ca->delay_max < delay)
 187                 ca->delay_max = delay;
 188
 189         /* utilization is low, if avg delay < dist*threshold
 190            for checking_period time */
 191         dist = ca->delay_max - ca->delay_min;
 192         if (dist <= ca->delay_min>>6 ||
 193             tp->srtt - ca->delay_min >=  (dist*low_utilization_threshold)>>10)
 194                 goto notlow;
 195
 196         if (ca->low_utilization_start == 0) {
 197                 ca->low_utilization = 0;
 198                 ca->low_utilization_start = tcp_time_stamp;
 199         } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
 200                         > low_utilization_period*HZ) {
 201                 ca->low_utilization = 1;
 202         }
 203
 204         return;
 205
 206  notlow:
 207         ca->low_utilization = 0;
 208         ca->low_utilization_start = 0;
 209
 210 }
 211
 212 static void bictcp_cong_avoid(struct sock *sk, u32 ack,
 213                               u32 seq_rtt, u32 in_flight, int data_acked)
 214 {
 215         struct tcp_sock *tp = tcp_sk(sk);
 216         struct bictcp *ca = inet_csk_ca(sk);
 217
 218         bictcp_low_utilization(sk, data_acked);
 219
 220         if (in_flight < tp->snd_cwnd)
 221                 return;
 222
 223         if (tp->snd_cwnd <= tp->snd_ssthresh) {
 224                 /* In "safe" area, increase. */
 225                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 226                         tp->snd_cwnd++;
 227         } else {
 228                 bictcp_update(ca, tp->snd_cwnd);
 229
 230                 /* In dangerous area, increase slowly.
 231                  * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 232                  */
 233                 if (tp->snd_cwnd_cnt >= ca->cnt) {
 234                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 235                                 tp->snd_cwnd++;
 236                         tp->snd_cwnd_cnt = 0;
 237                 } else
 238                         tp->snd_cwnd_cnt++;
 239         }
 240
 241 }
 242
 243 /*
 244  *      behave like Reno until low_window is reached,
 245  *      then increase congestion window slowly
 246  */
 247 static u32 bictcp_recalc_ssthresh(struct sock *sk)
 248 {
 249         const struct tcp_sock *tp = tcp_sk(sk);
 250         struct bictcp *ca = inet_csk_ca(sk);
 251
 252         ca->epoch_start = 0;    /* end of epoch */
 253
 254         /* in case of wrong delay_max*/
 255         if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
 256                 ca->delay_max = ca->delay_min
 257                         + ((ca->delay_max - ca->delay_min)* 90) / 100;
 258
 259         /* Wmax and fast convergence */
 260         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 261                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 262                         / (2 * BICTCP_BETA_SCALE);
 263         else
 264                 ca->last_max_cwnd = tp->snd_cwnd;
 265
 266         ca->loss_cwnd = tp->snd_cwnd;
 267
 268
 269         if (tp->snd_cwnd <= low_window)
 270                 return max(tp->snd_cwnd >> 1U, 2U);
 271         else
 272                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 273 }
 274
 275 static u32 bictcp_undo_cwnd(struct sock *sk)
 276 {
 277         const struct tcp_sock *tp = tcp_sk(sk);
 278         const struct bictcp *ca = inet_csk_ca(sk);
 279         return max(tp->snd_cwnd, ca->last_max_cwnd);
 280 }
 281
 282 static u32 bictcp_min_cwnd(struct sock *sk)
 283 {
 284         const struct tcp_sock *tp = tcp_sk(sk);
 285         return tp->snd_ssthresh;
 286 }
 287
 288 static void bictcp_state(struct sock *sk, u8 new_state)
 289 {
 290         if (new_state == TCP_CA_Loss)
 291                 bictcp_reset(inet_csk_ca(sk));
 292 }
 293
 294 /* Track delayed acknowledgement ratio using sliding window
 295  * ratio = (15*ratio + sample) / 16
 296  */
 297 static void bictcp_acked(struct sock *sk, u32 cnt)
 298 {
 299         const struct inet_connection_sock *icsk = inet_csk(sk);
 300
 301         if (cnt > 0 &&  icsk->icsk_ca_state == TCP_CA_Open) {
 302                 struct bictcp *ca = inet_csk_ca(sk);
 303                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 304                 ca->delayed_ack += cnt;
 305         }
 306 }
 307
 308
 309 static struct tcp_congestion_ops bictcp = {
 310         .init           = bictcp_init,
 311         .ssthresh       = bictcp_recalc_ssthresh,
 312         .cong_avoid     = bictcp_cong_avoid,
 313         .set_state      = bictcp_state,
 314         .undo_cwnd      = bictcp_undo_cwnd,
 315         .min_cwnd       = bictcp_min_cwnd,
 316         .pkts_acked     = bictcp_acked,
 317         .owner          = THIS_MODULE,
 318         .name           = "bic",
 319 };
 320
 321 static int __init bictcp_register(void)
 322 {
 323         BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 324         return tcp_register_congestion_control(&bictcp);
 325 }
 326
 327 static void __exit bictcp_unregister(void)
 328 {
 329         tcp_unregister_congestion_control(&bictcp);
 330 }
 331
 332 module_init(bictcp_register);
 333 module_exit(bictcp_unregister);
 334
 335 MODULE_AUTHOR("Stephen Hemminger");
 336 MODULE_LICENSE("GPL");
 337 MODULE_DESCRIPTION("BIC TCP");