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 tcp_sock *tp)
  90 {
  91         bictcp_reset(tcp_ca(tp));
  92         if (initial_ssthresh)
  93                 tp->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 tcp_sock *tp, int flag)
 160 {
 161         struct bictcp *ca = tcp_ca(tp);
 162         u32 dist, delay;
 163
 164         /* No time stamp */
 165         if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
 166              /* Discard delay samples right after fast recovery */
 167              tcp_time_stamp < ca->epoch_start + HZ ||
 168              /* this delay samples may not be accurate */
 169              flag == 0) {
 170                 ca->last_delay = 0;
 171                 goto notlow;
 172         }
 173
 174         delay = ca->last_delay<<3;      /* use the same scale as tp->srtt*/
 175         ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
 176         if (delay == 0)                 /* no previous delay sample */
 177                 goto notlow;
 178
 179         /* first time call or link delay decreases */
 180         if (ca->delay_min == 0 || ca->delay_min > delay) {
 181                 ca->delay_min = ca->delay_max = delay;
 182                 goto notlow;
 183         }
 184
 185         if (ca->delay_max < delay)
 186                 ca->delay_max = delay;
 187
 188         /* utilization is low, if avg delay < dist*threshold
 189            for checking_period time */
 190         dist = ca->delay_max - ca->delay_min;
 191         if (dist <= ca->delay_min>>6 ||
 192             tp->srtt - ca->delay_min >=  (dist*low_utilization_threshold)>>10)
 193                 goto notlow;
 194
 195         if (ca->low_utilization_start == 0) {
 196                 ca->low_utilization = 0;
 197                 ca->low_utilization_start = tcp_time_stamp;
 198         } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
 199                         > low_utilization_period*HZ) {
 200                 ca->low_utilization = 1;
 201         }
 202
 203         return;
 204
 205  notlow:
 206         ca->low_utilization = 0;
 207         ca->low_utilization_start = 0;
 208
 209 }
 210
 211 static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
 212                               u32 seq_rtt, u32 in_flight, int data_acked)
 213 {
 214         struct bictcp *ca = tcp_ca(tp);
 215
 216         bictcp_low_utilization(tp, data_acked);
 217
 218         if (in_flight < tp->snd_cwnd)
 219                 return;
 220
 221         if (tp->snd_cwnd <= tp->snd_ssthresh) {
 222                 /* In "safe" area, increase. */
 223                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 224                         tp->snd_cwnd++;
 225         } else {
 226                 bictcp_update(ca, tp->snd_cwnd);
 227
 228                 /* In dangerous area, increase slowly.
 229                  * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 230                  */
 231                 if (tp->snd_cwnd_cnt >= ca->cnt) {
 232                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 233                                 tp->snd_cwnd++;
 234                         tp->snd_cwnd_cnt = 0;
 235                 } else
 236                         tp->snd_cwnd_cnt++;
 237         }
 238
 239 }
 240
 241 /*
 242  *      behave like Reno until low_window is reached,
 243  *      then increase congestion window slowly
 244  */
 245 static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
 246 {
 247         struct bictcp *ca = tcp_ca(tp);
 248
 249         ca->epoch_start = 0;    /* end of epoch */
 250
 251         /* in case of wrong delay_max*/
 252         if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
 253                 ca->delay_max = ca->delay_min
 254                         + ((ca->delay_max - ca->delay_min)* 90) / 100;
 255
 256         /* Wmax and fast convergence */
 257         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 258                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 259                         / (2 * BICTCP_BETA_SCALE);
 260         else
 261                 ca->last_max_cwnd = tp->snd_cwnd;
 262
 263         ca->loss_cwnd = tp->snd_cwnd;
 264
 265
 266         if (tp->snd_cwnd <= low_window)
 267                 return max(tp->snd_cwnd >> 1U, 2U);
 268         else
 269                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 270 }
 271
 272 static u32 bictcp_undo_cwnd(struct tcp_sock *tp)
 273 {
 274         struct bictcp *ca = tcp_ca(tp);
 275
 276         return max(tp->snd_cwnd, ca->last_max_cwnd);
 277 }
 278
 279 static u32 bictcp_min_cwnd(struct tcp_sock *tp)
 280 {
 281         return tp->snd_ssthresh;
 282 }
 283
 284 static void bictcp_state(struct tcp_sock *tp, u8 new_state)
 285 {
 286         if (new_state == TCP_CA_Loss)
 287                 bictcp_reset(tcp_ca(tp));
 288 }
 289
 290 /* Track delayed acknowledgement ratio using sliding window
 291  * ratio = (15*ratio + sample) / 16
 292  */
 293 static void bictcp_acked(struct tcp_sock *tp, u32 cnt)
 294 {
 295         if (cnt > 0 &&  tp->ca_state == TCP_CA_Open) {
 296                 struct bictcp *ca = tcp_ca(tp);
 297                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 298                 ca->delayed_ack += cnt;
 299         }
 300 }
 301
 302
 303 static struct tcp_congestion_ops bictcp = {
 304         .init           = bictcp_init,
 305         .ssthresh       = bictcp_recalc_ssthresh,
 306         .cong_avoid     = bictcp_cong_avoid,
 307         .set_state      = bictcp_state,
 308         .undo_cwnd      = bictcp_undo_cwnd,
 309         .min_cwnd       = bictcp_min_cwnd,
 310         .pkts_acked     = bictcp_acked,
 311         .owner          = THIS_MODULE,
 312         .name           = "bic",
 313 };
 314
 315 static int __init bictcp_register(void)
 316 {
 317         BUG_ON(sizeof(struct bictcp) > TCP_CA_PRIV_SIZE);
 318         return tcp_register_congestion_control(&bictcp);
 319 }
 320
 321 static void __exit bictcp_unregister(void)
 322 {
 323         tcp_unregister_congestion_control(&bictcp);
 324 }
 325
 326 module_init(bictcp_register);
 327 module_exit(bictcp_unregister);
 328
 329 MODULE_AUTHOR("Stephen Hemminger");
 330 MODULE_LICENSE("GPL");
 331 MODULE_DESCRIPTION("BIC TCP");