net/ipv4/tcp_veno.c

   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.ntu.edu.sg/home5/ZHOU0022/papers/CPFu03a.pdf
  10  */
  11
  12 #include <linux/config.h>
  13 #include <linux/mm.h>
  14 #include <linux/module.h>
  15 #include <linux/skbuff.h>
  16 #include <linux/inet_diag.h>
  17
  18 #include <net/tcp.h>
  19
  20 /* Default values of the Veno variables, in fixed-point representation
  21  * with V_PARAM_SHIFT bits to the right of the binary point.
  22  */
  23 #define V_PARAM_SHIFT 1
  24 static const int beta = 3 << V_PARAM_SHIFT;
  25
  26 /* Veno variables */
  27 struct veno {
  28         u8 doing_veno_now;      /* if true, do veno for this rtt */
  29         u16 cntrtt;             /* # of rtts measured within last rtt */
  30         u32 minrtt;             /* min of rtts measured within last rtt (in usec) */
  31         u32 basertt;            /* the min of all Veno rtt measurements seen (in usec) */
  32         u32 inc;                /* decide whether to increase cwnd */
  33         u32 diff;               /* calculate the diff rate */
  34 };
  35
  36 /* There are several situations when we must "re-start" Veno:
  37  *
  38  *  o when a connection is established
  39  *  o after an RTO
  40  *  o after fast recovery
  41  *  o when we send a packet and there is no outstanding
  42  *    unacknowledged data (restarting an idle connection)
  43  *
  44  */
  45 static inline void veno_enable(struct sock *sk)
  46 {
  47         struct veno *veno = inet_csk_ca(sk);
  48
  49         /* turn on Veno */
  50         veno->doing_veno_now = 1;
  51
  52         veno->minrtt = 0x7fffffff;
  53 }
  54
  55 static inline void veno_disable(struct sock *sk)
  56 {
  57         struct veno *veno = inet_csk_ca(sk);
  58
  59         /* turn off Veno */
  60         veno->doing_veno_now = 0;
  61 }
  62
  63 static void tcp_veno_init(struct sock *sk)
  64 {
  65         struct veno *veno = inet_csk_ca(sk);
  66
  67         veno->basertt = 0x7fffffff;
  68         veno->inc = 1;
  69         veno_enable(sk);
  70 }
  71
  72 /* Do rtt sampling needed for Veno. */
  73 static void tcp_veno_rtt_calc(struct sock *sk, u32 usrtt)
  74 {
  75         struct veno *veno = inet_csk_ca(sk);
  76         u32 vrtt = usrtt + 1;   /* Never allow zero rtt or basertt */
  77
  78         /* Filter to find propagation delay: */
  79         if (vrtt < veno->basertt)
  80                 veno->basertt = vrtt;
  81
  82         /* Find the min rtt during the last rtt to find
  83          * the current prop. delay + queuing delay:
  84          */
  85         veno->minrtt = min(veno->minrtt, vrtt);
  86         veno->cntrtt++;
  87 }
  88
  89 static void tcp_veno_state(struct sock *sk, u8 ca_state)
  90 {
  91         if (ca_state == TCP_CA_Open)
  92                 veno_enable(sk);
  93         else
  94                 veno_disable(sk);
  95 }
  96
  97 /*
  98  * If the connection is idle and we are restarting,
  99  * then we don't want to do any Veno calculations
 100  * until we get fresh rtt samples.  So when we
 101  * restart, we reset our Veno state to a clean
 102  * state. After we get acks for this flight of
 103  * packets, _then_ we can make Veno calculations
 104  * again.
 105  */
 106 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
 107 {
 108         if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
 109                 tcp_veno_init(sk);
 110 }
 111
 112 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack,
 113                                 u32 seq_rtt, u32 in_flight, int flag)
 114 {
 115         struct tcp_sock *tp = tcp_sk(sk);
 116         struct veno *veno = inet_csk_ca(sk);
 117
 118         if (!veno->doing_veno_now)
 119                 return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
 120
 121         /* limited by applications */
 122         if (!tcp_is_cwnd_limited(sk, in_flight))
 123                 return;
 124
 125         /* We do the Veno calculations only if we got enough rtt samples */
 126         if (veno->cntrtt <= 2) {
 127                 /* We don't have enough rtt samples to do the Veno
 128                  * calculation, so we'll behave like Reno.
 129                  */
 130                 tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
 131         } else {
 132                 u32 rtt, target_cwnd;
 133
 134                 /* We have enough rtt samples, so, using the Veno
 135                  * algorithm, we determine the state of the network.
 136                  */
 137
 138                 rtt = veno->minrtt;
 139
 140                 target_cwnd = ((tp->snd_cwnd * veno->basertt)
 141                                << V_PARAM_SHIFT) / rtt;
 142
 143                 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
 144
 145                 if (tp->snd_cwnd <= tp->snd_ssthresh) {
 146                         /* Slow start.  */
 147                         tcp_slow_start(tp);
 148                 } else {
 149                         /* Congestion avoidance. */
 150                         if (veno->diff < beta) {
 151                                 /* In the "non-congestive state", increase cwnd
 152                                  *  every rtt.
 153                                  */
 154                                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 155                                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 156                                                 tp->snd_cwnd++;
 157                                         tp->snd_cwnd_cnt = 0;
 158                                 } else
 159                                         tp->snd_cwnd_cnt++;
 160                         } else {
 161                                 /* In the "congestive state", increase cwnd
 162                                  * every other rtt.
 163                                  */
 164                                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 165                                         if (veno->inc
 166                                             && tp->snd_cwnd <
 167                                             tp->snd_cwnd_clamp) {
 168                                                 tp->snd_cwnd++;
 169                                                 veno->inc = 0;
 170                                         } else
 171                                                 veno->inc = 1;
 172                                         tp->snd_cwnd_cnt = 0;
 173                                 } else
 174                                         tp->snd_cwnd_cnt++;
 175                         }
 176
 177                 }
 178                 if (tp->snd_cwnd < 2)
 179                         tp->snd_cwnd = 2;
 180                 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
 181                         tp->snd_cwnd = tp->snd_cwnd_clamp;
 182         }
 183         /* Wipe the slate clean for the next rtt. */
 184         /* veno->cntrtt = 0; */
 185         veno->minrtt = 0x7fffffff;
 186 }
 187
 188 /* Veno MD phase */
 189 static u32 tcp_veno_ssthresh(struct sock *sk)
 190 {
 191         const struct tcp_sock *tp = tcp_sk(sk);
 192         struct veno *veno = inet_csk_ca(sk);
 193
 194         if (veno->diff < beta)
 195                 /* in "non-congestive state", cut cwnd by 1/5 */
 196                 return max(tp->snd_cwnd * 4 / 5, 2U);
 197         else
 198                 /* in "congestive state", cut cwnd by 1/2 */
 199                 return max(tp->snd_cwnd >> 1U, 2U);
 200 }
 201
 202 static struct tcp_congestion_ops tcp_veno = {
 203         .init           = tcp_veno_init,
 204         .ssthresh       = tcp_veno_ssthresh,
 205         .cong_avoid     = tcp_veno_cong_avoid,
 206         .rtt_sample     = tcp_veno_rtt_calc,
 207         .set_state      = tcp_veno_state,
 208         .cwnd_event     = tcp_veno_cwnd_event,
 209
 210         .owner          = THIS_MODULE,
 211         .name           = "veno",
 212 };
 213
 214 static int __init tcp_veno_register(void)
 215 {
 216         BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
 217         tcp_register_congestion_control(&tcp_veno);
 218         return 0;
 219 }
 220
 221 static void __exit tcp_veno_unregister(void)
 222 {
 223         tcp_unregister_congestion_control(&tcp_veno);
 224 }
 225
 226 module_init(tcp_veno_register);
 227 module_exit(tcp_veno_unregister);
 228
 229 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
 230 MODULE_LICENSE("GPL");
 231 MODULE_DESCRIPTION("TCP Veno");