1 /* 2 * 3 * YeAH TCP 4 * 5 * For further details look at: 6 * https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf 7 * 8 */ 9 #include <linux/mm.h> 10 #include <linux/module.h> 11 #include <linux/skbuff.h> 12 #include <linux/inet_diag.h> 13 14 #include <net/tcp.h> 15 16 #include "tcp_vegas.h" 17 18 #define TCP_YEAH_ALPHA 80 /* number of packets queued at the bottleneck */ 19 #define TCP_YEAH_GAMMA 1 /* fraction of queue to be removed per rtt */ 20 #define TCP_YEAH_DELTA 3 /* log minimum fraction of cwnd to be removed on loss */ 21 #define TCP_YEAH_EPSILON 1 /* log maximum fraction to be removed on early decongestion */ 22 #define TCP_YEAH_PHY 8 /* maximum delta from base */ 23 #define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */ 24 #define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */ 25 26 #define TCP_SCALABLE_AI_CNT 100U 27 28 /* YeAH variables */ 29 struct yeah { 30 struct vegas vegas; /* must be first */ 31 32 /* YeAH */ 33 u32 lastQ; 34 u32 doing_reno_now; 35 36 u32 reno_count; 37 u32 fast_count; 38 39 u32 pkts_acked; 40 u32 loss_cwnd; 41 }; 42 43 static void tcp_yeah_init(struct sock *sk) 44 { 45 struct tcp_sock *tp = tcp_sk(sk); 46 struct yeah *yeah = inet_csk_ca(sk); 47 48 tcp_vegas_init(sk); 49 50 yeah->doing_reno_now = 0; 51 yeah->lastQ = 0; 52 53 yeah->reno_count = 2; 54 55 /* Ensure the MD arithmetic works. This is somewhat pedantic, 56 * since I don't think we will see a cwnd this large. :) */ 57 tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); 58 } 59 60 static void tcp_yeah_pkts_acked(struct sock *sk, 61 const struct ack_sample *sample) 62 { 63 const struct inet_connection_sock *icsk = inet_csk(sk); 64 struct yeah *yeah = inet_csk_ca(sk); 65 66 if (icsk->icsk_ca_state == TCP_CA_Open) 67 yeah->pkts_acked = sample->pkts_acked; 68 69 tcp_vegas_pkts_acked(sk, sample); 70 } 71 72 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked) 73 { 74 struct tcp_sock *tp = tcp_sk(sk); 75 struct yeah *yeah = inet_csk_ca(sk); 76 77 if (!tcp_is_cwnd_limited(sk)) 78 return; 79 80 if (tcp_in_slow_start(tp)) 81 tcp_slow_start(tp, acked); 82 83 else if (!yeah->doing_reno_now) { 84 /* Scalable */ 85 86 tp->snd_cwnd_cnt += yeah->pkts_acked; 87 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) { 88 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 89 tp->snd_cwnd++; 90 tp->snd_cwnd_cnt = 0; 91 } 92 93 yeah->pkts_acked = 1; 94 95 } else { 96 /* Reno */ 97 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 98 } 99 100 /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. 101 * 102 * These are so named because they represent the approximate values 103 * of snd_una and snd_nxt at the beginning of the current RTT. More 104 * precisely, they represent the amount of data sent during the RTT. 105 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, 106 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding 107 * bytes of data have been ACKed during the course of the RTT, giving 108 * an "actual" rate of: 109 * 110 * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) 111 * 112 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, 113 * because delayed ACKs can cover more than one segment, so they 114 * don't line up yeahly with the boundaries of RTTs. 115 * 116 * Another unfortunate fact of life is that delayed ACKs delay the 117 * advance of the left edge of our send window, so that the number 118 * of bytes we send in an RTT is often less than our cwnd will allow. 119 * So we keep track of our cwnd separately, in v_beg_snd_cwnd. 120 */ 121 122 if (after(ack, yeah->vegas.beg_snd_nxt)) { 123 /* We do the Vegas calculations only if we got enough RTT 124 * samples that we can be reasonably sure that we got 125 * at least one RTT sample that wasn't from a delayed ACK. 126 * If we only had 2 samples total, 127 * then that means we're getting only 1 ACK per RTT, which 128 * means they're almost certainly delayed ACKs. 129 * If we have 3 samples, we should be OK. 130 */ 131 132 if (yeah->vegas.cntRTT > 2) { 133 u32 rtt, queue; 134 u64 bw; 135 136 /* We have enough RTT samples, so, using the Vegas 137 * algorithm, we determine if we should increase or 138 * decrease cwnd, and by how much. 139 */ 140 141 /* Pluck out the RTT we are using for the Vegas 142 * calculations. This is the min RTT seen during the 143 * last RTT. Taking the min filters out the effects 144 * of delayed ACKs, at the cost of noticing congestion 145 * a bit later. 146 */ 147 rtt = yeah->vegas.minRTT; 148 149 /* Compute excess number of packets above bandwidth 150 * Avoid doing full 64 bit divide. 151 */ 152 bw = tp->snd_cwnd; 153 bw *= rtt - yeah->vegas.baseRTT; 154 do_div(bw, rtt); 155 queue = bw; 156 157 if (queue > TCP_YEAH_ALPHA || 158 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { 159 if (queue > TCP_YEAH_ALPHA && 160 tp->snd_cwnd > yeah->reno_count) { 161 u32 reduction = min(queue / TCP_YEAH_GAMMA , 162 tp->snd_cwnd >> TCP_YEAH_EPSILON); 163 164 tp->snd_cwnd -= reduction; 165 166 tp->snd_cwnd = max(tp->snd_cwnd, 167 yeah->reno_count); 168 169 tp->snd_ssthresh = tp->snd_cwnd; 170 } 171 172 if (yeah->reno_count <= 2) 173 yeah->reno_count = max(tp->snd_cwnd>>1, 2U); 174 else 175 yeah->reno_count++; 176 177 yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 178 0xffffffU); 179 } else { 180 yeah->fast_count++; 181 182 if (yeah->fast_count > TCP_YEAH_ZETA) { 183 yeah->reno_count = 2; 184 yeah->fast_count = 0; 185 } 186 187 yeah->doing_reno_now = 0; 188 } 189 190 yeah->lastQ = queue; 191 } 192 193 /* Save the extent of the current window so we can use this 194 * at the end of the next RTT. 195 */ 196 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; 197 yeah->vegas.beg_snd_nxt = tp->snd_nxt; 198 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; 199 200 /* Wipe the slate clean for the next RTT. */ 201 yeah->vegas.cntRTT = 0; 202 yeah->vegas.minRTT = 0x7fffffff; 203 } 204 } 205 206 static u32 tcp_yeah_ssthresh(struct sock *sk) 207 { 208 const struct tcp_sock *tp = tcp_sk(sk); 209 struct yeah *yeah = inet_csk_ca(sk); 210 u32 reduction; 211 212 if (yeah->doing_reno_now < TCP_YEAH_RHO) { 213 reduction = yeah->lastQ; 214 215 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); 216 217 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); 218 } else 219 reduction = max(tp->snd_cwnd>>1, 2U); 220 221 yeah->fast_count = 0; 222 yeah->reno_count = max(yeah->reno_count>>1, 2U); 223 yeah->loss_cwnd = tp->snd_cwnd; 224 225 return max_t(int, tp->snd_cwnd - reduction, 2); 226 } 227 228 static u32 tcp_yeah_cwnd_undo(struct sock *sk) 229 { 230 const struct yeah *yeah = inet_csk_ca(sk); 231 232 return max(tcp_sk(sk)->snd_cwnd, yeah->loss_cwnd); 233 } 234 235 static struct tcp_congestion_ops tcp_yeah __read_mostly = { 236 .init = tcp_yeah_init, 237 .ssthresh = tcp_yeah_ssthresh, 238 .undo_cwnd = tcp_yeah_cwnd_undo, 239 .cong_avoid = tcp_yeah_cong_avoid, 240 .set_state = tcp_vegas_state, 241 .cwnd_event = tcp_vegas_cwnd_event, 242 .get_info = tcp_vegas_get_info, 243 .pkts_acked = tcp_yeah_pkts_acked, 244 245 .owner = THIS_MODULE, 246 .name = "yeah", 247 }; 248 249 static int __init tcp_yeah_register(void) 250 { 251 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); 252 tcp_register_congestion_control(&tcp_yeah); 253 return 0; 254 } 255 256 static void __exit tcp_yeah_unregister(void) 257 { 258 tcp_unregister_congestion_control(&tcp_yeah); 259 } 260 261 module_init(tcp_yeah_register); 262 module_exit(tcp_yeah_unregister); 263 264 MODULE_AUTHOR("Angelo P. Castellani"); 265 MODULE_LICENSE("GPL"); 266 MODULE_DESCRIPTION("YeAH TCP"); 267