1 /* 2 * TCP Westwood+: end-to-end bandwidth estimation for TCP 3 * 4 * Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4 5 * 6 * Support at http://c3lab.poliba.it/index.php/Westwood 7 * Main references in literature: 8 * 9 * - Mascolo S, Casetti, M. Gerla et al. 10 * "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001 11 * 12 * - A. Grieco, s. Mascolo 13 * "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer 14 * Comm. Review, 2004 15 * 16 * - A. Dell'Aera, L. Grieco, S. Mascolo. 17 * "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving : 18 * A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004 19 * 20 * Westwood+ employs end-to-end bandwidth measurement to set cwnd and 21 * ssthresh after packet loss. The probing phase is as the original Reno. 22 */ 23 24 #include <linux/mm.h> 25 #include <linux/module.h> 26 #include <linux/skbuff.h> 27 #include <linux/inet_diag.h> 28 #include <net/tcp.h> 29 30 /* TCP Westwood structure */ 31 struct westwood { 32 u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */ 33 u32 bw_est; /* bandwidth estimate */ 34 u32 rtt_win_sx; /* here starts a new evaluation... */ 35 u32 bk; 36 u32 snd_una; /* used for evaluating the number of acked bytes */ 37 u32 cumul_ack; 38 u32 accounted; 39 u32 rtt; 40 u32 rtt_min; /* minimum observed RTT */ 41 u8 first_ack; /* flag which infers that this is the first ack */ 42 u8 reset_rtt_min; /* Reset RTT min to next RTT sample*/ 43 }; 44 45 46 /* TCP Westwood functions and constants */ 47 #define TCP_WESTWOOD_RTT_MIN (HZ/20) /* 50ms */ 48 #define TCP_WESTWOOD_INIT_RTT (20*HZ) /* maybe too conservative?! */ 49 50 /* 51 * @tcp_westwood_create 52 * This function initializes fields used in TCP Westwood+, 53 * it is called after the initial SYN, so the sequence numbers 54 * are correct but new passive connections we have no 55 * information about RTTmin at this time so we simply set it to 56 * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative 57 * since in this way we're sure it will be updated in a consistent 58 * way as soon as possible. It will reasonably happen within the first 59 * RTT period of the connection lifetime. 60 */ 61 static void tcp_westwood_init(struct sock *sk) 62 { 63 struct westwood *w = inet_csk_ca(sk); 64 65 w->bk = 0; 66 w->bw_ns_est = 0; 67 w->bw_est = 0; 68 w->accounted = 0; 69 w->cumul_ack = 0; 70 w->reset_rtt_min = 1; 71 w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT; 72 w->rtt_win_sx = tcp_time_stamp; 73 w->snd_una = tcp_sk(sk)->snd_una; 74 w->first_ack = 1; 75 } 76 77 /* 78 * @westwood_do_filter 79 * Low-pass filter. Implemented using constant coefficients. 80 */ 81 static inline u32 westwood_do_filter(u32 a, u32 b) 82 { 83 return (((7 * a) + b) >> 3); 84 } 85 86 static void westwood_filter(struct westwood *w, u32 delta) 87 { 88 /* If the filter is empty fill it with the first sample of bandwidth */ 89 if (w->bw_ns_est == 0 && w->bw_est == 0) { 90 w->bw_ns_est = w->bk / delta; 91 w->bw_est = w->bw_ns_est; 92 } else { 93 w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta); 94 w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est); 95 } 96 } 97 98 /* 99 * @westwood_pkts_acked 100 * Called after processing group of packets. 101 * but all westwood needs is the last sample of srtt. 102 */ 103 static void tcp_westwood_pkts_acked(struct sock *sk, u32 cnt) 104 { 105 struct westwood *w = inet_csk_ca(sk); 106 if (cnt > 0) 107 w->rtt = tcp_sk(sk)->srtt >> 3; 108 } 109 110 /* 111 * @westwood_update_window 112 * It updates RTT evaluation window if it is the right moment to do 113 * it. If so it calls filter for evaluating bandwidth. 114 */ 115 static void westwood_update_window(struct sock *sk) 116 { 117 struct westwood *w = inet_csk_ca(sk); 118 s32 delta = tcp_time_stamp - w->rtt_win_sx; 119 120 /* Initialize w->snd_una with the first acked sequence number in order 121 * to fix mismatch between tp->snd_una and w->snd_una for the first 122 * bandwidth sample 123 */ 124 if (w->first_ack) { 125 w->snd_una = tcp_sk(sk)->snd_una; 126 w->first_ack = 0; 127 } 128 129 /* 130 * See if a RTT-window has passed. 131 * Be careful since if RTT is less than 132 * 50ms we don't filter but we continue 'building the sample'. 133 * This minimum limit was chosen since an estimation on small 134 * time intervals is better to avoid... 135 * Obviously on a LAN we reasonably will always have 136 * right_bound = left_bound + WESTWOOD_RTT_MIN 137 */ 138 if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) { 139 westwood_filter(w, delta); 140 141 w->bk = 0; 142 w->rtt_win_sx = tcp_time_stamp; 143 } 144 } 145 146 static inline void update_rtt_min(struct westwood *w) 147 { 148 if (w->reset_rtt_min) { 149 w->rtt_min = w->rtt; 150 w->reset_rtt_min = 0; 151 } else 152 w->rtt_min = min(w->rtt, w->rtt_min); 153 } 154 155 156 /* 157 * @westwood_fast_bw 158 * It is called when we are in fast path. In particular it is called when 159 * header prediction is successful. In such case in fact update is 160 * straight forward and doesn't need any particular care. 161 */ 162 static inline void westwood_fast_bw(struct sock *sk) 163 { 164 const struct tcp_sock *tp = tcp_sk(sk); 165 struct westwood *w = inet_csk_ca(sk); 166 167 westwood_update_window(sk); 168 169 w->bk += tp->snd_una - w->snd_una; 170 w->snd_una = tp->snd_una; 171 update_rtt_min(w); 172 } 173 174 /* 175 * @westwood_acked_count 176 * This function evaluates cumul_ack for evaluating bk in case of 177 * delayed or partial acks. 178 */ 179 static inline u32 westwood_acked_count(struct sock *sk) 180 { 181 const struct tcp_sock *tp = tcp_sk(sk); 182 struct westwood *w = inet_csk_ca(sk); 183 184 w->cumul_ack = tp->snd_una - w->snd_una; 185 186 /* If cumul_ack is 0 this is a dupack since it's not moving 187 * tp->snd_una. 188 */ 189 if (!w->cumul_ack) { 190 w->accounted += tp->mss_cache; 191 w->cumul_ack = tp->mss_cache; 192 } 193 194 if (w->cumul_ack > tp->mss_cache) { 195 /* Partial or delayed ack */ 196 if (w->accounted >= w->cumul_ack) { 197 w->accounted -= w->cumul_ack; 198 w->cumul_ack = tp->mss_cache; 199 } else { 200 w->cumul_ack -= w->accounted; 201 w->accounted = 0; 202 } 203 } 204 205 w->snd_una = tp->snd_una; 206 207 return w->cumul_ack; 208 } 209 210 211 /* 212 * TCP Westwood 213 * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it 214 * in packets we use mss_cache). Rttmin is guaranteed to be >= 2 215 * so avoids ever returning 0. 216 */ 217 static u32 tcp_westwood_bw_rttmin(const struct sock *sk) 218 { 219 const struct tcp_sock *tp = tcp_sk(sk); 220 const struct westwood *w = inet_csk_ca(sk); 221 return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2); 222 } 223 224 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event) 225 { 226 struct tcp_sock *tp = tcp_sk(sk); 227 struct westwood *w = inet_csk_ca(sk); 228 229 switch(event) { 230 case CA_EVENT_FAST_ACK: 231 westwood_fast_bw(sk); 232 break; 233 234 case CA_EVENT_COMPLETE_CWR: 235 tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); 236 break; 237 238 case CA_EVENT_FRTO: 239 tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); 240 /* Update RTT_min when next ack arrives */ 241 w->reset_rtt_min = 1; 242 break; 243 244 case CA_EVENT_SLOW_ACK: 245 westwood_update_window(sk); 246 w->bk += westwood_acked_count(sk); 247 update_rtt_min(w); 248 break; 249 250 default: 251 /* don't care */ 252 break; 253 } 254 } 255 256 257 /* Extract info for Tcp socket info provided via netlink. */ 258 static void tcp_westwood_info(struct sock *sk, u32 ext, 259 struct sk_buff *skb) 260 { 261 const struct westwood *ca = inet_csk_ca(sk); 262 if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 263 struct rtattr *rta; 264 struct tcpvegas_info *info; 265 266 rta = __RTA_PUT(skb, INET_DIAG_VEGASINFO, sizeof(*info)); 267 info = RTA_DATA(rta); 268 info->tcpv_enabled = 1; 269 info->tcpv_rttcnt = 0; 270 info->tcpv_rtt = jiffies_to_usecs(ca->rtt); 271 info->tcpv_minrtt = jiffies_to_usecs(ca->rtt_min); 272 rtattr_failure: ; 273 } 274 } 275 276 277 static struct tcp_congestion_ops tcp_westwood = { 278 .init = tcp_westwood_init, 279 .ssthresh = tcp_reno_ssthresh, 280 .cong_avoid = tcp_reno_cong_avoid, 281 .min_cwnd = tcp_westwood_bw_rttmin, 282 .cwnd_event = tcp_westwood_event, 283 .get_info = tcp_westwood_info, 284 .pkts_acked = tcp_westwood_pkts_acked, 285 286 .owner = THIS_MODULE, 287 .name = "westwood" 288 }; 289 290 static int __init tcp_westwood_register(void) 291 { 292 BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE); 293 return tcp_register_congestion_control(&tcp_westwood); 294 } 295 296 static void __exit tcp_westwood_unregister(void) 297 { 298 tcp_unregister_congestion_control(&tcp_westwood); 299 } 300 301 module_init(tcp_westwood_register); 302 module_exit(tcp_westwood_unregister); 303 304 MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera"); 305 MODULE_LICENSE("GPL"); 306 MODULE_DESCRIPTION("TCP Westwood+"); 307