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 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 u32 loss_cwnd; /* cwnd when loss occured */ 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 tcp_slow_start(tp, acked); 158 } else { 159 /* Congestion avoidance. */ 160 if (veno->diff < beta) { 161 /* In the "non-congestive state", increase cwnd 162 * every rtt. 163 */ 164 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 165 } else { 166 /* In the "congestive state", increase cwnd 167 * every other rtt. 168 */ 169 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 170 if (veno->inc && 171 tp->snd_cwnd < tp->snd_cwnd_clamp) { 172 tp->snd_cwnd++; 173 veno->inc = 0; 174 } else 175 veno->inc = 1; 176 tp->snd_cwnd_cnt = 0; 177 } else 178 tp->snd_cwnd_cnt++; 179 } 180 } 181 if (tp->snd_cwnd < 2) 182 tp->snd_cwnd = 2; 183 else if (tp->snd_cwnd > tp->snd_cwnd_clamp) 184 tp->snd_cwnd = tp->snd_cwnd_clamp; 185 } 186 /* Wipe the slate clean for the next rtt. */ 187 /* veno->cntrtt = 0; */ 188 veno->minrtt = 0x7fffffff; 189 } 190 191 /* Veno MD phase */ 192 static u32 tcp_veno_ssthresh(struct sock *sk) 193 { 194 const struct tcp_sock *tp = tcp_sk(sk); 195 struct veno *veno = inet_csk_ca(sk); 196 197 veno->loss_cwnd = tp->snd_cwnd; 198 if (veno->diff < beta) 199 /* in "non-congestive state", cut cwnd by 1/5 */ 200 return max(tp->snd_cwnd * 4 / 5, 2U); 201 else 202 /* in "congestive state", cut cwnd by 1/2 */ 203 return max(tp->snd_cwnd >> 1U, 2U); 204 } 205 206 static u32 tcp_veno_cwnd_undo(struct sock *sk) 207 { 208 const struct veno *veno = inet_csk_ca(sk); 209 210 return max(tcp_sk(sk)->snd_cwnd, veno->loss_cwnd); 211 } 212 213 static struct tcp_congestion_ops tcp_veno __read_mostly = { 214 .init = tcp_veno_init, 215 .ssthresh = tcp_veno_ssthresh, 216 .undo_cwnd = tcp_veno_cwnd_undo, 217 .cong_avoid = tcp_veno_cong_avoid, 218 .pkts_acked = tcp_veno_pkts_acked, 219 .set_state = tcp_veno_state, 220 .cwnd_event = tcp_veno_cwnd_event, 221 222 .owner = THIS_MODULE, 223 .name = "veno", 224 }; 225 226 static int __init tcp_veno_register(void) 227 { 228 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE); 229 tcp_register_congestion_control(&tcp_veno); 230 return 0; 231 } 232 233 static void __exit tcp_veno_unregister(void) 234 { 235 tcp_unregister_congestion_control(&tcp_veno); 236 } 237 238 module_init(tcp_veno_register); 239 module_exit(tcp_veno_unregister); 240 241 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu"); 242 MODULE_LICENSE("GPL"); 243 MODULE_DESCRIPTION("TCP Veno"); 244