net/ipv4/tcp_veno.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * TCP Veno congestion control
   4  *
   5  * This is based on the congestion detection/avoidance scheme described in
   6  *    C. P. Fu, S. C. Liew.
   7  *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
   8  *    IEEE Journal on Selected Areas in Communication,
   9  *    Feb. 2003.
  10  *      See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
  11  */
  12
  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_pkts_acked(struct sock *sk,
  74                                 const struct ack_sample *sample)
  75 {
  76         struct veno *veno = inet_csk_ca(sk);
  77         u32 vrtt;
  78
  79         if (sample->rtt_us < 0)
  80                 return;
  81
  82         /* Never allow zero rtt or baseRTT */
  83         vrtt = sample->rtt_us + 1;
  84
  85         /* Filter to find propagation delay: */
  86         if (vrtt < veno->basertt)
  87                 veno->basertt = vrtt;
  88
  89         /* Find the min rtt during the last rtt to find
  90          * the current prop. delay + queuing delay:
  91          */
  92         veno->minrtt = min(veno->minrtt, vrtt);
  93         veno->cntrtt++;
  94 }
  95
  96 static void tcp_veno_state(struct sock *sk, u8 ca_state)
  97 {
  98         if (ca_state == TCP_CA_Open)
  99                 veno_enable(sk);
 100         else
 101                 veno_disable(sk);
 102 }
 103
 104 /*
 105  * If the connection is idle and we are restarting,
 106  * then we don't want to do any Veno calculations
 107  * until we get fresh rtt samples.  So when we
 108  * restart, we reset our Veno state to a clean
 109  * state. After we get acks for this flight of
 110  * packets, _then_ we can make Veno calculations
 111  * again.
 112  */
 113 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
 114 {
 115         if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
 116                 tcp_veno_init(sk);
 117 }
 118
 119 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 120 {
 121         struct tcp_sock *tp = tcp_sk(sk);
 122         struct veno *veno = inet_csk_ca(sk);
 123
 124         if (!veno->doing_veno_now) {
 125                 tcp_reno_cong_avoid(sk, ack, acked);
 126                 return;
 127         }
 128
 129         /* limited by applications */
 130         if (!tcp_is_cwnd_limited(sk))
 131                 return;
 132
 133         /* We do the Veno calculations only if we got enough rtt samples */
 134         if (veno->cntrtt <= 2) {
 135                 /* We don't have enough rtt samples to do the Veno
 136                  * calculation, so we'll behave like Reno.
 137                  */
 138                 tcp_reno_cong_avoid(sk, ack, acked);
 139         } else {
 140                 u64 target_cwnd;
 141                 u32 rtt;
 142
 143                 /* We have enough rtt samples, so, using the Veno
 144                  * algorithm, we determine the state of the network.
 145                  */
 146
 147                 rtt = veno->minrtt;
 148
 149                 target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
 150                 target_cwnd <<= V_PARAM_SHIFT;
 151                 do_div(target_cwnd, rtt);
 152
 153                 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
 154
 155                 if (tcp_in_slow_start(tp)) {
 156                         /* Slow start. */
 157                         acked = tcp_slow_start(tp, acked);
 158                         if (!acked)
 159                                 goto done;
 160                 }
 161
 162                 /* Congestion avoidance. */
 163                 if (veno->diff < beta) {
 164                         /* In the "non-congestive state", increase cwnd
 165                          * every rtt.
 166                          */
 167                         tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 168                 } else {
 169                         /* In the "congestive state", increase cwnd
 170                          * every other rtt.
 171                          */
 172                         if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 173                                 if (veno->inc &&
 174                                     tp->snd_cwnd < tp->snd_cwnd_clamp) {
 175                                         tp->snd_cwnd++;
 176                                         veno->inc = 0;
 177                                 } else
 178                                         veno->inc = 1;
 179                                 tp->snd_cwnd_cnt = 0;
 180                         } else
 181                                 tp->snd_cwnd_cnt += acked;
 182                 }
 183 done:
 184                 if (tp->snd_cwnd < 2)
 185                         tp->snd_cwnd = 2;
 186                 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
 187                         tp->snd_cwnd = tp->snd_cwnd_clamp;
 188         }
 189         /* Wipe the slate clean for the next rtt. */
 190         /* veno->cntrtt = 0; */
 191         veno->minrtt = 0x7fffffff;
 192 }
 193
 194 /* Veno MD phase */
 195 static u32 tcp_veno_ssthresh(struct sock *sk)
 196 {
 197         const struct tcp_sock *tp = tcp_sk(sk);
 198         struct veno *veno = inet_csk_ca(sk);
 199
 200         if (veno->diff < beta)
 201                 /* in "non-congestive state", cut cwnd by 1/5 */
 202                 return max(tp->snd_cwnd * 4 / 5, 2U);
 203         else
 204                 /* in "congestive state", cut cwnd by 1/2 */
 205                 return max(tp->snd_cwnd >> 1U, 2U);
 206 }
 207
 208 static struct tcp_congestion_ops tcp_veno __read_mostly = {
 209         .init           = tcp_veno_init,
 210         .ssthresh       = tcp_veno_ssthresh,
 211         .undo_cwnd      = tcp_reno_undo_cwnd,
 212         .cong_avoid     = tcp_veno_cong_avoid,
 213         .pkts_acked     = tcp_veno_pkts_acked,
 214         .set_state      = tcp_veno_state,
 215         .cwnd_event     = tcp_veno_cwnd_event,
 216
 217         .owner          = THIS_MODULE,
 218         .name           = "veno",
 219 };
 220
 221 static int __init tcp_veno_register(void)
 222 {
 223         BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
 224         tcp_register_congestion_control(&tcp_veno);
 225         return 0;
 226 }
 227
 228 static void __exit tcp_veno_unregister(void)
 229 {
 230         tcp_unregister_congestion_control(&tcp_veno);
 231 }
 232
 233 module_init(tcp_veno_register);
 234 module_exit(tcp_veno_unregister);
 235
 236 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
 237 MODULE_LICENSE("GPL");
 238 MODULE_DESCRIPTION("TCP Veno");