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/mm.h>
  16 #include <linux/module.h>
  17 #include <net/tcp.h>
  18
  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
  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     loss_cwnd;      /* congestion window at last loss */
  54         u32     last_cwnd;      /* the last snd_cwnd */
  55         u32     last_time;      /* time when updated last_cwnd */
  56         u32     epoch_start;    /* beginning of an epoch */
  57 #define ACK_RATIO_SHIFT 4
  58         u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
  59 };
  60
  61 static inline void bictcp_reset(struct bictcp *ca)
  62 {
  63         ca->cnt = 0;
  64         ca->last_max_cwnd = 0;
  65         ca->loss_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         bictcp_reset(inet_csk_ca(sk));
  75         if (initial_ssthresh)
  76                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
  77 }
  78
  79 /*
  80  * Compute congestion window to use.
  81  */
  82 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
  83 {
  84         if (ca->last_cwnd == cwnd &&
  85             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
  86                 return;
  87
  88         ca->last_cwnd = cwnd;
  89         ca->last_time = tcp_time_stamp;
  90
  91         if (ca->epoch_start == 0) /* record the beginning of an epoch */
  92                 ca->epoch_start = tcp_time_stamp;
  93
  94         /* start off normal */
  95         if (cwnd <= low_window) {
  96                 ca->cnt = cwnd;
  97                 return;
  98         }
  99
 100         /* binary increase */
 101         if (cwnd < ca->last_max_cwnd) {
 102                 __u32   dist = (ca->last_max_cwnd - cwnd)
 103                         / BICTCP_B;
 104
 105                 if (dist > max_increment)
 106                         /* linear increase */
 107                         ca->cnt = cwnd / max_increment;
 108                 else if (dist <= 1U)
 109                         /* binary search increase */
 110                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 111                 else
 112                         /* binary search increase */
 113                         ca->cnt = cwnd / dist;
 114         } else {
 115                 /* slow start AMD linear increase */
 116                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
 117                         /* slow start */
 118                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
 119                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
 120                         /* slow start */
 121                         ca->cnt = (cwnd * (BICTCP_B-1))
 122                                 / (cwnd - ca->last_max_cwnd);
 123                 else
 124                         /* linear increase */
 125                         ca->cnt = cwnd / max_increment;
 126         }
 127
 128         /* if in slow start or link utilization is very low */
 129         if (ca->loss_cwnd == 0) {
 130                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
 131                         ca->cnt = 20;
 132         }
 133
 134         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
 135         if (ca->cnt == 0)                       /* cannot be zero */
 136                 ca->cnt = 1;
 137 }
 138
 139 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 140 {
 141         struct tcp_sock *tp = tcp_sk(sk);
 142         struct bictcp *ca = inet_csk_ca(sk);
 143
 144         if (!tcp_is_cwnd_limited(sk, in_flight))
 145                 return;
 146
 147         if (tp->snd_cwnd <= tp->snd_ssthresh)
 148                 tcp_slow_start(tp);
 149         else {
 150                 bictcp_update(ca, tp->snd_cwnd);
 151
 152                 /* In dangerous area, increase slowly.
 153                  * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 154                  */
 155                 if (tp->snd_cwnd_cnt >= ca->cnt) {
 156                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 157                                 tp->snd_cwnd++;
 158                         tp->snd_cwnd_cnt = 0;
 159                 } else
 160                         tp->snd_cwnd_cnt++;
 161         }
 162
 163 }
 164
 165 /*
 166  *      behave like Reno until low_window is reached,
 167  *      then increase congestion window slowly
 168  */
 169 static u32 bictcp_recalc_ssthresh(struct sock *sk)
 170 {
 171         const struct tcp_sock *tp = tcp_sk(sk);
 172         struct bictcp *ca = inet_csk_ca(sk);
 173
 174         ca->epoch_start = 0;    /* end of epoch */
 175
 176         /* Wmax and fast convergence */
 177         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
 178                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
 179                         / (2 * BICTCP_BETA_SCALE);
 180         else
 181                 ca->last_max_cwnd = tp->snd_cwnd;
 182
 183         ca->loss_cwnd = tp->snd_cwnd;
 184
 185
 186         if (tp->snd_cwnd <= low_window)
 187                 return max(tp->snd_cwnd >> 1U, 2U);
 188         else
 189                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 190 }
 191
 192 static u32 bictcp_undo_cwnd(struct sock *sk)
 193 {
 194         const struct tcp_sock *tp = tcp_sk(sk);
 195         const struct bictcp *ca = inet_csk_ca(sk);
 196         return max(tp->snd_cwnd, ca->last_max_cwnd);
 197 }
 198
 199 static void bictcp_state(struct sock *sk, u8 new_state)
 200 {
 201         if (new_state == TCP_CA_Loss)
 202                 bictcp_reset(inet_csk_ca(sk));
 203 }
 204
 205 /* Track delayed acknowledgment ratio using sliding window
 206  * ratio = (15*ratio + sample) / 16
 207  */
 208 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
 209 {
 210         const struct inet_connection_sock *icsk = inet_csk(sk);
 211
 212         if (icsk->icsk_ca_state == TCP_CA_Open) {
 213                 struct bictcp *ca = inet_csk_ca(sk);
 214                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
 215                 ca->delayed_ack += cnt;
 216         }
 217 }
 218
 219
 220 static struct tcp_congestion_ops bictcp = {
 221         .init           = bictcp_init,
 222         .ssthresh       = bictcp_recalc_ssthresh,
 223         .cong_avoid     = bictcp_cong_avoid,
 224         .set_state      = bictcp_state,
 225         .undo_cwnd      = bictcp_undo_cwnd,
 226         .pkts_acked     = bictcp_acked,
 227         .owner          = THIS_MODULE,
 228         .name           = "bic",
 229 };
 230
 231 static int __init bictcp_register(void)
 232 {
 233         BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 234         return tcp_register_congestion_control(&bictcp);
 235 }
 236
 237 static void __exit bictcp_unregister(void)
 238 {
 239         tcp_unregister_congestion_control(&bictcp);
 240 }
 241
 242 module_init(bictcp_register);
 243 module_exit(bictcp_unregister);
 244
 245 MODULE_AUTHOR("Stephen Hemminger");
 246 MODULE_LICENSE("GPL");
 247 MODULE_DESCRIPTION("BIC TCP");