linux/net/ipv4/tcp_veno.c
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   1/*
   2 * TCP Veno congestion control
   3 *
   4 * This is based on the congestion detection/avoidance scheme described in
   5 *    C. P. Fu, S. C. Liew.
   6 *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
   7 *    IEEE Journal on Selected Areas in Communication,
   8 *    Feb. 2003.
   9 *      See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
  10 */
  11
  12#include <linux/mm.h>
  13#include <linux/module.h>
  14#include <linux/skbuff.h>
  15#include <linux/inet_diag.h>
  16
  17#include <net/tcp.h>
  18
  19/* Default values of the Veno variables, in fixed-point representation
  20 * with V_PARAM_SHIFT bits to the right of the binary point.
  21 */
  22#define V_PARAM_SHIFT 1
  23static const int beta = 3 << V_PARAM_SHIFT;
  24
  25/* Veno variables */
  26struct veno {
  27        u8 doing_veno_now;      /* if true, do veno for this rtt */
  28        u16 cntrtt;             /* # of rtts measured within last rtt */
  29        u32 minrtt;             /* min of rtts measured within last rtt (in usec) */
  30        u32 basertt;            /* the min of all Veno rtt measurements seen (in usec) */
  31        u32 inc;                /* decide whether to increase cwnd */
  32        u32 diff;               /* calculate the diff rate */
  33};
  34
  35/* There are several situations when we must "re-start" Veno:
  36 *
  37 *  o when a connection is established
  38 *  o after an RTO
  39 *  o after fast recovery
  40 *  o when we send a packet and there is no outstanding
  41 *    unacknowledged data (restarting an idle connection)
  42 *
  43 */
  44static inline void veno_enable(struct sock *sk)
  45{
  46        struct veno *veno = inet_csk_ca(sk);
  47
  48        /* turn on Veno */
  49        veno->doing_veno_now = 1;
  50
  51        veno->minrtt = 0x7fffffff;
  52}
  53
  54static inline void veno_disable(struct sock *sk)
  55{
  56        struct veno *veno = inet_csk_ca(sk);
  57
  58        /* turn off Veno */
  59        veno->doing_veno_now = 0;
  60}
  61
  62static void tcp_veno_init(struct sock *sk)
  63{
  64        struct veno *veno = inet_csk_ca(sk);
  65
  66        veno->basertt = 0x7fffffff;
  67        veno->inc = 1;
  68        veno_enable(sk);
  69}
  70
  71/* Do rtt sampling needed for Veno. */
  72static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
  73{
  74        struct veno *veno = inet_csk_ca(sk);
  75        u32 vrtt;
  76
  77        if (rtt_us < 0)
  78                return;
  79
  80        /* Never allow zero rtt or baseRTT */
  81        vrtt = rtt_us + 1;
  82
  83        /* Filter to find propagation delay: */
  84        if (vrtt < veno->basertt)
  85                veno->basertt = vrtt;
  86
  87        /* Find the min rtt during the last rtt to find
  88         * the current prop. delay + queuing delay:
  89         */
  90        veno->minrtt = min(veno->minrtt, vrtt);
  91        veno->cntrtt++;
  92}
  93
  94static void tcp_veno_state(struct sock *sk, u8 ca_state)
  95{
  96        if (ca_state == TCP_CA_Open)
  97                veno_enable(sk);
  98        else
  99                veno_disable(sk);
 100}
 101
 102/*
 103 * If the connection is idle and we are restarting,
 104 * then we don't want to do any Veno calculations
 105 * until we get fresh rtt samples.  So when we
 106 * restart, we reset our Veno state to a clean
 107 * state. After we get acks for this flight of
 108 * packets, _then_ we can make Veno calculations
 109 * again.
 110 */
 111static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
 112{
 113        if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
 114                tcp_veno_init(sk);
 115}
 116
 117static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 118{
 119        struct tcp_sock *tp = tcp_sk(sk);
 120        struct veno *veno = inet_csk_ca(sk);
 121
 122        if (!veno->doing_veno_now) {
 123                tcp_reno_cong_avoid(sk, ack, in_flight);
 124                return;
 125        }
 126
 127        /* limited by applications */
 128        if (!tcp_is_cwnd_limited(sk, in_flight))
 129                return;
 130
 131        /* We do the Veno calculations only if we got enough rtt samples */
 132        if (veno->cntrtt <= 2) {
 133                /* We don't have enough rtt samples to do the Veno
 134                 * calculation, so we'll behave like Reno.
 135                 */
 136                tcp_reno_cong_avoid(sk, ack, in_flight);
 137        } else {
 138                u64 target_cwnd;
 139                u32 rtt;
 140
 141                /* We have enough rtt samples, so, using the Veno
 142                 * algorithm, we determine the state of the network.
 143                 */
 144
 145                rtt = veno->minrtt;
 146
 147                target_cwnd = (tp->snd_cwnd * veno->basertt);
 148                target_cwnd <<= V_PARAM_SHIFT;
 149                do_div(target_cwnd, rtt);
 150
 151                veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
 152
 153                if (tp->snd_cwnd <= tp->snd_ssthresh) {
 154                        /* Slow start.  */
 155                        tcp_slow_start(tp);
 156                } else {
 157                        /* Congestion avoidance. */
 158                        if (veno->diff < beta) {
 159                                /* In the "non-congestive state", increase cwnd
 160                                 *  every rtt.
 161                                 */
 162                                tcp_cong_avoid_ai(tp, tp->snd_cwnd);
 163                        } else {
 164                                /* In the "congestive state", increase cwnd
 165                                 * every other rtt.
 166                                 */
 167                                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 168                                        if (veno->inc &&
 169                                            tp->snd_cwnd < tp->snd_cwnd_clamp) {
 170                                                tp->snd_cwnd++;
 171                                                veno->inc = 0;
 172                                        } else
 173                                                veno->inc = 1;
 174                                        tp->snd_cwnd_cnt = 0;
 175                                } else
 176                                        tp->snd_cwnd_cnt++;
 177                        }
 178
 179                }
 180                if (tp->snd_cwnd < 2)
 181                        tp->snd_cwnd = 2;
 182                else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
 183                        tp->snd_cwnd = tp->snd_cwnd_clamp;
 184        }
 185        /* Wipe the slate clean for the next rtt. */
 186        /* veno->cntrtt = 0; */
 187        veno->minrtt = 0x7fffffff;
 188}
 189
 190/* Veno MD phase */
 191static u32 tcp_veno_ssthresh(struct sock *sk)
 192{
 193        const struct tcp_sock *tp = tcp_sk(sk);
 194        struct veno *veno = inet_csk_ca(sk);
 195
 196        if (veno->diff < beta)
 197                /* in "non-congestive state", cut cwnd by 1/5 */
 198                return max(tp->snd_cwnd * 4 / 5, 2U);
 199        else
 200                /* in "congestive state", cut cwnd by 1/2 */
 201                return max(tp->snd_cwnd >> 1U, 2U);
 202}
 203
 204static struct tcp_congestion_ops tcp_veno __read_mostly = {
 205        .flags          = TCP_CONG_RTT_STAMP,
 206        .init           = tcp_veno_init,
 207        .ssthresh       = tcp_veno_ssthresh,
 208        .cong_avoid     = tcp_veno_cong_avoid,
 209        .pkts_acked     = tcp_veno_pkts_acked,
 210        .set_state      = tcp_veno_state,
 211        .cwnd_event     = tcp_veno_cwnd_event,
 212
 213        .owner          = THIS_MODULE,
 214        .name           = "veno",
 215};
 216
 217static int __init tcp_veno_register(void)
 218{
 219        BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
 220        tcp_register_congestion_control(&tcp_veno);
 221        return 0;
 222}
 223
 224static void __exit tcp_veno_unregister(void)
 225{
 226        tcp_unregister_congestion_control(&tcp_veno);
 227}
 228
 229module_init(tcp_veno_register);
 230module_exit(tcp_veno_unregister);
 231
 232MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
 233MODULE_LICENSE("GPL");
 234MODULE_DESCRIPTION("TCP Veno");
 235
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