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/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 23 static const int beta = 3 << V_PARAM_SHIFT; 24 25 /* Veno variables */ 26 struct 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 */ 44 static 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 54 static 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 62 static 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. */ 72 static void tcp_veno_rtt_calc(struct sock *sk, u32 usrtt) 73 { 74 struct veno *veno = inet_csk_ca(sk); 75 u32 vrtt = usrtt + 1; /* Never allow zero rtt or basertt */ 76 77 /* Filter to find propagation delay: */ 78 if (vrtt < veno->basertt) 79 veno->basertt = vrtt; 80 81 /* Find the min rtt during the last rtt to find 82 * the current prop. delay + queuing delay: 83 */ 84 veno->minrtt = min(veno->minrtt, vrtt); 85 veno->cntrtt++; 86 } 87 88 static void tcp_veno_state(struct sock *sk, u8 ca_state) 89 { 90 if (ca_state == TCP_CA_Open) 91 veno_enable(sk); 92 else 93 veno_disable(sk); 94 } 95 96 /* 97 * If the connection is idle and we are restarting, 98 * then we don't want to do any Veno calculations 99 * until we get fresh rtt samples. So when we 100 * restart, we reset our Veno state to a clean 101 * state. After we get acks for this flight of 102 * packets, _then_ we can make Veno calculations 103 * again. 104 */ 105 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event) 106 { 107 if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START) 108 tcp_veno_init(sk); 109 } 110 111 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, 112 u32 seq_rtt, u32 in_flight, int flag) 113 { 114 struct tcp_sock *tp = tcp_sk(sk); 115 struct veno *veno = inet_csk_ca(sk); 116 117 if (!veno->doing_veno_now) 118 return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag); 119 120 /* limited by applications */ 121 if (!tcp_is_cwnd_limited(sk, in_flight)) 122 return; 123 124 /* We do the Veno calculations only if we got enough rtt samples */ 125 if (veno->cntrtt <= 2) { 126 /* We don't have enough rtt samples to do the Veno 127 * calculation, so we'll behave like Reno. 128 */ 129 tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag); 130 } else { 131 u32 rtt, target_cwnd; 132 133 /* We have enough rtt samples, so, using the Veno 134 * algorithm, we determine the state of the network. 135 */ 136 137 rtt = veno->minrtt; 138 139 target_cwnd = ((tp->snd_cwnd * veno->basertt) 140 << V_PARAM_SHIFT) / rtt; 141 142 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd; 143 144 if (tp->snd_cwnd <= tp->snd_ssthresh) { 145 /* Slow start. */ 146 tcp_slow_start(tp); 147 } else { 148 /* Congestion avoidance. */ 149 if (veno->diff < beta) { 150 /* In the "non-congestive state", increase cwnd 151 * every rtt. 152 */ 153 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 154 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 155 tp->snd_cwnd++; 156 tp->snd_cwnd_cnt = 0; 157 } else 158 tp->snd_cwnd_cnt++; 159 } else { 160 /* In the "congestive state", increase cwnd 161 * every other rtt. 162 */ 163 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 164 if (veno->inc 165 && tp->snd_cwnd < 166 tp->snd_cwnd_clamp) { 167 tp->snd_cwnd++; 168 veno->inc = 0; 169 } else 170 veno->inc = 1; 171 tp->snd_cwnd_cnt = 0; 172 } else 173 tp->snd_cwnd_cnt++; 174 } 175 176 } 177 if (tp->snd_cwnd < 2) 178 tp->snd_cwnd = 2; 179 else if (tp->snd_cwnd > tp->snd_cwnd_clamp) 180 tp->snd_cwnd = tp->snd_cwnd_clamp; 181 } 182 /* Wipe the slate clean for the next rtt. */ 183 /* veno->cntrtt = 0; */ 184 veno->minrtt = 0x7fffffff; 185 } 186 187 /* Veno MD phase */ 188 static u32 tcp_veno_ssthresh(struct sock *sk) 189 { 190 const struct tcp_sock *tp = tcp_sk(sk); 191 struct veno *veno = inet_csk_ca(sk); 192 193 if (veno->diff < beta) 194 /* in "non-congestive state", cut cwnd by 1/5 */ 195 return max(tp->snd_cwnd * 4 / 5, 2U); 196 else 197 /* in "congestive state", cut cwnd by 1/2 */ 198 return max(tp->snd_cwnd >> 1U, 2U); 199 } 200 201 static struct tcp_congestion_ops tcp_veno = { 202 .init = tcp_veno_init, 203 .ssthresh = tcp_veno_ssthresh, 204 .cong_avoid = tcp_veno_cong_avoid, 205 .rtt_sample = tcp_veno_rtt_calc, 206 .set_state = tcp_veno_state, 207 .cwnd_event = tcp_veno_cwnd_event, 208 209 .owner = THIS_MODULE, 210 .name = "veno", 211 }; 212 213 static int __init tcp_veno_register(void) 214 { 215 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE); 216 tcp_register_congestion_control(&tcp_veno); 217 return 0; 218 } 219 220 static void __exit tcp_veno_unregister(void) 221 { 222 tcp_unregister_congestion_control(&tcp_veno); 223 } 224 225 module_init(tcp_veno_register); 226 module_exit(tcp_veno_unregister); 227 228 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu"); 229 MODULE_LICENSE("GPL"); 230 MODULE_DESCRIPTION("TCP Veno"); 231