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, u32 cnt, s32 rtt_us) 73 { 74 struct veno *veno = inet_csk_ca(sk); 75 u32 vrtt; 76 77 if (rtt_us < 0) 78 return; 79 80 /* Never allow zero rtt or baseRTT */ 81 vrtt = rtt_us + 1; 82 83 /* Filter to find propagation delay: */ 84 if (vrtt < veno->basertt) 85 veno->basertt = vrtt; 86 87 /* Find the min rtt during the last rtt to find 88 * the current prop. delay + queuing delay: 89 */ 90 veno->minrtt = min(veno->minrtt, vrtt); 91 veno->cntrtt++; 92 } 93 94 static void tcp_veno_state(struct sock *sk, u8 ca_state) 95 { 96 if (ca_state == TCP_CA_Open) 97 veno_enable(sk); 98 else 99 veno_disable(sk); 100 } 101 102 /* 103 * If the connection is idle and we are restarting, 104 * then we don't want to do any Veno calculations 105 * until we get fresh rtt samples. So when we 106 * restart, we reset our Veno state to a clean 107 * state. After we get acks for this flight of 108 * packets, _then_ we can make Veno calculations 109 * again. 110 */ 111 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event) 112 { 113 if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START) 114 tcp_veno_init(sk); 115 } 116 117 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked) 118 { 119 struct tcp_sock *tp = tcp_sk(sk); 120 struct veno *veno = inet_csk_ca(sk); 121 122 if (!veno->doing_veno_now) { 123 tcp_reno_cong_avoid(sk, ack, acked); 124 return; 125 } 126 127 /* limited by applications */ 128 if (!tcp_is_cwnd_limited(sk)) 129 return; 130 131 /* We do the Veno calculations only if we got enough rtt samples */ 132 if (veno->cntrtt <= 2) { 133 /* We don't have enough rtt samples to do the Veno 134 * calculation, so we'll behave like Reno. 135 */ 136 tcp_reno_cong_avoid(sk, ack, acked); 137 } else { 138 u64 target_cwnd; 139 u32 rtt; 140 141 /* We have enough rtt samples, so, using the Veno 142 * algorithm, we determine the state of the network. 143 */ 144 145 rtt = veno->minrtt; 146 147 target_cwnd = (u64)tp->snd_cwnd * veno->basertt; 148 target_cwnd <<= V_PARAM_SHIFT; 149 do_div(target_cwnd, rtt); 150 151 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd; 152 153 if (tcp_in_slow_start(tp)) { 154 /* Slow start. */ 155 tcp_slow_start(tp, acked); 156 } else { 157 /* Congestion avoidance. */ 158 if (veno->diff < beta) { 159 /* In the "non-congestive state", increase cwnd 160 * every rtt. 161 */ 162 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 163 } else { 164 /* In the "congestive state", increase cwnd 165 * every other rtt. 166 */ 167 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 168 if (veno->inc && 169 tp->snd_cwnd < tp->snd_cwnd_clamp) { 170 tp->snd_cwnd++; 171 veno->inc = 0; 172 } else 173 veno->inc = 1; 174 tp->snd_cwnd_cnt = 0; 175 } else 176 tp->snd_cwnd_cnt++; 177 } 178 } 179 if (tp->snd_cwnd < 2) 180 tp->snd_cwnd = 2; 181 else if (tp->snd_cwnd > tp->snd_cwnd_clamp) 182 tp->snd_cwnd = tp->snd_cwnd_clamp; 183 } 184 /* Wipe the slate clean for the next rtt. */ 185 /* veno->cntrtt = 0; */ 186 veno->minrtt = 0x7fffffff; 187 } 188 189 /* Veno MD phase */ 190 static u32 tcp_veno_ssthresh(struct sock *sk) 191 { 192 const struct tcp_sock *tp = tcp_sk(sk); 193 struct veno *veno = inet_csk_ca(sk); 194 195 if (veno->diff < beta) 196 /* in "non-congestive state", cut cwnd by 1/5 */ 197 return max(tp->snd_cwnd * 4 / 5, 2U); 198 else 199 /* in "congestive state", cut cwnd by 1/2 */ 200 return max(tp->snd_cwnd >> 1U, 2U); 201 } 202 203 static struct tcp_congestion_ops tcp_veno __read_mostly = { 204 .init = tcp_veno_init, 205 .ssthresh = tcp_veno_ssthresh, 206 .cong_avoid = tcp_veno_cong_avoid, 207 .pkts_acked = tcp_veno_pkts_acked, 208 .set_state = tcp_veno_state, 209 .cwnd_event = tcp_veno_cwnd_event, 210 211 .owner = THIS_MODULE, 212 .name = "veno", 213 }; 214 215 static int __init tcp_veno_register(void) 216 { 217 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE); 218 tcp_register_congestion_control(&tcp_veno); 219 return 0; 220 } 221 222 static void __exit tcp_veno_unregister(void) 223 { 224 tcp_unregister_congestion_control(&tcp_veno); 225 } 226 227 module_init(tcp_veno_register); 228 module_exit(tcp_veno_unregister); 229 230 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu"); 231 MODULE_LICENSE("GPL"); 232 MODULE_DESCRIPTION("TCP Veno"); 233