1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * TCP Westwood+: end-to-end bandwidth estimation for TCP 4 * 5 * Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4 6 * 7 * Support at http://c3lab.poliba.it/index.php/Westwood 8 * Main references in literature: 9 * 10 * - Mascolo S, Casetti, M. Gerla et al. 11 * "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001 12 * 13 * - A. Grieco, s. Mascolo 14 * "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer 15 * Comm. Review, 2004 16 * 17 * - A. Dell'Aera, L. Grieco, S. Mascolo. 18 * "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving : 19 * A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004 20 * 21 * Westwood+ employs end-to-end bandwidth measurement to set cwnd and 22 * ssthresh after packet loss. The probing phase is as the original Reno. 23 */ 24 25 #include <linux/mm.h> 26 #include <linux/module.h> 27 #include <linux/skbuff.h> 28 #include <linux/inet_diag.h> 29 #include <net/tcp.h> 30 31 /* TCP Westwood structure */ 32 struct westwood { 33 u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */ 34 u32 bw_est; /* bandwidth estimate */ 35 u32 rtt_win_sx; /* here starts a new evaluation... */ 36 u32 bk; 37 u32 snd_una; /* used for evaluating the number of acked bytes */ 38 u32 cumul_ack; 39 u32 accounted; 40 u32 rtt; 41 u32 rtt_min; /* minimum observed RTT */ 42 u8 first_ack; /* flag which infers that this is the first ack */ 43 u8 reset_rtt_min; /* Reset RTT min to next RTT sample*/ 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_jiffies32; 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, 104 const struct ack_sample *sample) 105 { 106 struct westwood *w = inet_csk_ca(sk); 107 108 if (sample->rtt_us > 0) 109 w->rtt = usecs_to_jiffies(sample->rtt_us); 110 } 111 112 /* 113 * @westwood_update_window 114 * It updates RTT evaluation window if it is the right moment to do 115 * it. If so it calls filter for evaluating bandwidth. 116 */ 117 static void westwood_update_window(struct sock *sk) 118 { 119 struct westwood *w = inet_csk_ca(sk); 120 s32 delta = tcp_jiffies32 - w->rtt_win_sx; 121 122 /* Initialize w->snd_una with the first acked sequence number in order 123 * to fix mismatch between tp->snd_una and w->snd_una for the first 124 * bandwidth sample 125 */ 126 if (w->first_ack) { 127 w->snd_una = tcp_sk(sk)->snd_una; 128 w->first_ack = 0; 129 } 130 131 /* 132 * See if a RTT-window has passed. 133 * Be careful since if RTT is less than 134 * 50ms we don't filter but we continue 'building the sample'. 135 * This minimum limit was chosen since an estimation on small 136 * time intervals is better to avoid... 137 * Obviously on a LAN we reasonably will always have 138 * right_bound = left_bound + WESTWOOD_RTT_MIN 139 */ 140 if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) { 141 westwood_filter(w, delta); 142 143 w->bk = 0; 144 w->rtt_win_sx = tcp_jiffies32; 145 } 146 } 147 148 static inline void update_rtt_min(struct westwood *w) 149 { 150 if (w->reset_rtt_min) { 151 w->rtt_min = w->rtt; 152 w->reset_rtt_min = 0; 153 } else 154 w->rtt_min = min(w->rtt, w->rtt_min); 155 } 156 157 /* 158 * @westwood_fast_bw 159 * It is called when we are in fast path. In particular it is called when 160 * header prediction is successful. In such case in fact update is 161 * straight forward and doesn't need any particular care. 162 */ 163 static inline void westwood_fast_bw(struct sock *sk) 164 { 165 const struct tcp_sock *tp = tcp_sk(sk); 166 struct westwood *w = inet_csk_ca(sk); 167 168 westwood_update_window(sk); 169 170 w->bk += tp->snd_una - w->snd_una; 171 w->snd_una = tp->snd_una; 172 update_rtt_min(w); 173 } 174 175 /* 176 * @westwood_acked_count 177 * This function evaluates cumul_ack for evaluating bk in case of 178 * delayed or partial acks. 179 */ 180 static inline u32 westwood_acked_count(struct sock *sk) 181 { 182 const struct tcp_sock *tp = tcp_sk(sk); 183 struct westwood *w = inet_csk_ca(sk); 184 185 w->cumul_ack = tp->snd_una - w->snd_una; 186 187 /* If cumul_ack is 0 this is a dupack since it's not moving 188 * tp->snd_una. 189 */ 190 if (!w->cumul_ack) { 191 w->accounted += tp->mss_cache; 192 w->cumul_ack = tp->mss_cache; 193 } 194 195 if (w->cumul_ack > tp->mss_cache) { 196 /* Partial or delayed ack */ 197 if (w->accounted >= w->cumul_ack) { 198 w->accounted -= w->cumul_ack; 199 w->cumul_ack = tp->mss_cache; 200 } else { 201 w->cumul_ack -= w->accounted; 202 w->accounted = 0; 203 } 204 } 205 206 w->snd_una = tp->snd_una; 207 208 return w->cumul_ack; 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); 221 222 return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2); 223 } 224 225 static void tcp_westwood_ack(struct sock *sk, u32 ack_flags) 226 { 227 if (ack_flags & CA_ACK_SLOWPATH) { 228 struct westwood *w = inet_csk_ca(sk); 229 230 westwood_update_window(sk); 231 w->bk += westwood_acked_count(sk); 232 233 update_rtt_min(w); 234 return; 235 } 236 237 westwood_fast_bw(sk); 238 } 239 240 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event) 241 { 242 struct tcp_sock *tp = tcp_sk(sk); 243 struct westwood *w = inet_csk_ca(sk); 244 245 switch (event) { 246 case CA_EVENT_COMPLETE_CWR: 247 tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); 248 break; 249 case CA_EVENT_LOSS: 250 tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); 251 /* Update RTT_min when next ack arrives */ 252 w->reset_rtt_min = 1; 253 break; 254 default: 255 /* don't care */ 256 break; 257 } 258 } 259 260 /* Extract info for Tcp socket info provided via netlink. */ 261 static size_t tcp_westwood_info(struct sock *sk, u32 ext, int *attr, 262 union tcp_cc_info *info) 263 { 264 const struct westwood *ca = inet_csk_ca(sk); 265 266 if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 267 info->vegas.tcpv_enabled = 1; 268 info->vegas.tcpv_rttcnt = 0; 269 info->vegas.tcpv_rtt = jiffies_to_usecs(ca->rtt); 270 info->vegas.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min); 271 272 *attr = INET_DIAG_VEGASINFO; 273 return sizeof(struct tcpvegas_info); 274 } 275 return 0; 276 } 277 278 static struct tcp_congestion_ops tcp_westwood __read_mostly = { 279 .init = tcp_westwood_init, 280 .ssthresh = tcp_reno_ssthresh, 281 .cong_avoid = tcp_reno_cong_avoid, 282 .undo_cwnd = tcp_reno_undo_cwnd, 283 .cwnd_event = tcp_westwood_event, 284 .in_ack_event = tcp_westwood_ack, 285 .get_info = tcp_westwood_info, 286 .pkts_acked = tcp_westwood_pkts_acked, 287 288 .owner = THIS_MODULE, 289 .name = "westwood" 290 }; 291 292 static int __init tcp_westwood_register(void) 293 { 294 BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE); 295 return tcp_register_congestion_control(&tcp_westwood); 296 } 297 298 static void __exit tcp_westwood_unregister(void) 299 { 300 tcp_unregister_congestion_control(&tcp_westwood); 301 } 302 303 module_init(tcp_westwood_register); 304 module_exit(tcp_westwood_unregister); 305 306 MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera"); 307 MODULE_LICENSE("GPL"); 308 MODULE_DESCRIPTION("TCP Westwood+"); 309