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 }; 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_pkts_acked(struct sock *sk, 73 const struct ack_sample *sample) 74 { 75 struct veno *veno = inet_csk_ca(sk); 76 u32 vrtt; 77 78 if (sample->rtt_us < 0) 79 return; 80 81 /* Never allow zero rtt or baseRTT */ 82 vrtt = sample->rtt_us + 1; 83 84 /* Filter to find propagation delay: */ 85 if (vrtt < veno->basertt) 86 veno->basertt = vrtt; 87 88 /* Find the min rtt during the last rtt to find 89 * the current prop. delay + queuing delay: 90 */ 91 veno->minrtt = min(veno->minrtt, vrtt); 92 veno->cntrtt++; 93 } 94 95 static void tcp_veno_state(struct sock *sk, u8 ca_state) 96 { 97 if (ca_state == TCP_CA_Open) 98 veno_enable(sk); 99 else 100 veno_disable(sk); 101 } 102 103 /* 104 * If the connection is idle and we are restarting, 105 * then we don't want to do any Veno calculations 106 * until we get fresh rtt samples. So when we 107 * restart, we reset our Veno state to a clean 108 * state. After we get acks for this flight of 109 * packets, _then_ we can make Veno calculations 110 * again. 111 */ 112 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event) 113 { 114 if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START) 115 tcp_veno_init(sk); 116 } 117 118 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked) 119 { 120 struct tcp_sock *tp = tcp_sk(sk); 121 struct veno *veno = inet_csk_ca(sk); 122 123 if (!veno->doing_veno_now) { 124 tcp_reno_cong_avoid(sk, ack, acked); 125 return; 126 } 127 128 /* limited by applications */ 129 if (!tcp_is_cwnd_limited(sk)) 130 return; 131 132 /* We do the Veno calculations only if we got enough rtt samples */ 133 if (veno->cntrtt <= 2) { 134 /* We don't have enough rtt samples to do the Veno 135 * calculation, so we'll behave like Reno. 136 */ 137 tcp_reno_cong_avoid(sk, ack, acked); 138 } else { 139 u64 target_cwnd; 140 u32 rtt; 141 142 /* We have enough rtt samples, so, using the Veno 143 * algorithm, we determine the state of the network. 144 */ 145 146 rtt = veno->minrtt; 147 148 target_cwnd = (u64)tp->snd_cwnd * veno->basertt; 149 target_cwnd <<= V_PARAM_SHIFT; 150 do_div(target_cwnd, rtt); 151 152 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd; 153 154 if (tcp_in_slow_start(tp)) { 155 /* Slow start. */ 156 tcp_slow_start(tp, acked); 157 } else { 158 /* Congestion avoidance. */ 159 if (veno->diff < beta) { 160 /* In the "non-congestive state", increase cwnd 161 * every rtt. 162 */ 163 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 164 } else { 165 /* In the "congestive state", increase cwnd 166 * every other rtt. 167 */ 168 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 169 if (veno->inc && 170 tp->snd_cwnd < tp->snd_cwnd_clamp) { 171 tp->snd_cwnd++; 172 veno->inc = 0; 173 } else 174 veno->inc = 1; 175 tp->snd_cwnd_cnt = 0; 176 } else 177 tp->snd_cwnd_cnt++; 178 } 179 } 180 if (tp->snd_cwnd < 2) 181 tp->snd_cwnd = 2; 182 else if (tp->snd_cwnd > tp->snd_cwnd_clamp) 183 tp->snd_cwnd = tp->snd_cwnd_clamp; 184 } 185 /* Wipe the slate clean for the next rtt. */ 186 /* veno->cntrtt = 0; */ 187 veno->minrtt = 0x7fffffff; 188 } 189 190 /* Veno MD phase */ 191 static u32 tcp_veno_ssthresh(struct sock *sk) 192 { 193 const struct tcp_sock *tp = tcp_sk(sk); 194 struct veno *veno = inet_csk_ca(sk); 195 196 if (veno->diff < beta) 197 /* in "non-congestive state", cut cwnd by 1/5 */ 198 return max(tp->snd_cwnd * 4 / 5, 2U); 199 else 200 /* in "congestive state", cut cwnd by 1/2 */ 201 return max(tp->snd_cwnd >> 1U, 2U); 202 } 203 204 static struct tcp_congestion_ops tcp_veno __read_mostly = { 205 .init = tcp_veno_init, 206 .ssthresh = tcp_veno_ssthresh, 207 .undo_cwnd = tcp_reno_undo_cwnd, 208 .cong_avoid = tcp_veno_cong_avoid, 209 .pkts_acked = tcp_veno_pkts_acked, 210 .set_state = tcp_veno_state, 211 .cwnd_event = tcp_veno_cwnd_event, 212 213 .owner = THIS_MODULE, 214 .name = "veno", 215 }; 216 217 static int __init tcp_veno_register(void) 218 { 219 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE); 220 tcp_register_congestion_control(&tcp_veno); 221 return 0; 222 } 223 224 static void __exit tcp_veno_unregister(void) 225 { 226 tcp_unregister_congestion_control(&tcp_veno); 227 } 228 229 module_init(tcp_veno_register); 230 module_exit(tcp_veno_unregister); 231 232 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu"); 233 MODULE_LICENSE("GPL"); 234 MODULE_DESCRIPTION("TCP Veno"); 235