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"); 232