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 }; 41 42 static void tcp_yeah_init(struct sock *sk) 43 { 44 struct tcp_sock *tp = tcp_sk(sk); 45 struct yeah *yeah = inet_csk_ca(sk); 46 47 tcp_vegas_init(sk); 48 49 yeah->doing_reno_now = 0; 50 yeah->lastQ = 0; 51 52 yeah->reno_count = 2; 53 54 /* Ensure the MD arithmetic works. This is somewhat pedantic, 55 * since I don't think we will see a cwnd this large. :) */ 56 tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); 57 58 } 59 60 61 static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us) 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 = pkts_acked; 68 69 tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us); 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 (tp->snd_cwnd <= tp->snd_ssthresh) 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); 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)) { 123 124 /* We do the Vegas calculations only if we got enough RTT 125 * samples that we can be reasonably sure that we got 126 * at least one RTT sample that wasn't from a delayed ACK. 127 * If we only had 2 samples total, 128 * then that means we're getting only 1 ACK per RTT, which 129 * means they're almost certainly delayed ACKs. 130 * If we have 3 samples, we should be OK. 131 */ 132 133 if (yeah->vegas.cntRTT > 2) { 134 u32 rtt, queue; 135 u64 bw; 136 137 /* We have enough RTT samples, so, using the Vegas 138 * algorithm, we determine if we should increase or 139 * decrease cwnd, and by how much. 140 */ 141 142 /* Pluck out the RTT we are using for the Vegas 143 * calculations. This is the min RTT seen during the 144 * last RTT. Taking the min filters out the effects 145 * of delayed ACKs, at the cost of noticing congestion 146 * a bit later. 147 */ 148 rtt = yeah->vegas.minRTT; 149 150 /* Compute excess number of packets above bandwidth 151 * Avoid doing full 64 bit divide. 152 */ 153 bw = tp->snd_cwnd; 154 bw *= rtt - yeah->vegas.baseRTT; 155 do_div(bw, rtt); 156 queue = bw; 157 158 if (queue > TCP_YEAH_ALPHA || 159 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { 160 if (queue > TCP_YEAH_ALPHA && 161 tp->snd_cwnd > yeah->reno_count) { 162 u32 reduction = min(queue / TCP_YEAH_GAMMA , 163 tp->snd_cwnd >> TCP_YEAH_EPSILON); 164 165 tp->snd_cwnd -= reduction; 166 167 tp->snd_cwnd = max(tp->snd_cwnd, 168 yeah->reno_count); 169 170 tp->snd_ssthresh = tp->snd_cwnd; 171 } 172 173 if (yeah->reno_count <= 2) 174 yeah->reno_count = max(tp->snd_cwnd>>1, 2U); 175 else 176 yeah->reno_count++; 177 178 yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 179 0xffffffU); 180 } else { 181 yeah->fast_count++; 182 183 if (yeah->fast_count > TCP_YEAH_ZETA) { 184 yeah->reno_count = 2; 185 yeah->fast_count = 0; 186 } 187 188 yeah->doing_reno_now = 0; 189 } 190 191 yeah->lastQ = queue; 192 193 } 194 195 /* Save the extent of the current window so we can use this 196 * at the end of the next RTT. 197 */ 198 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; 199 yeah->vegas.beg_snd_nxt = tp->snd_nxt; 200 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; 201 202 /* Wipe the slate clean for the next RTT. */ 203 yeah->vegas.cntRTT = 0; 204 yeah->vegas.minRTT = 0x7fffffff; 205 } 206 } 207 208 static u32 tcp_yeah_ssthresh(struct sock *sk) { 209 const struct tcp_sock *tp = tcp_sk(sk); 210 struct yeah *yeah = inet_csk_ca(sk); 211 u32 reduction; 212 213 if (yeah->doing_reno_now < TCP_YEAH_RHO) { 214 reduction = yeah->lastQ; 215 216 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); 217 218 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); 219 } else 220 reduction = max(tp->snd_cwnd>>1, 2U); 221 222 yeah->fast_count = 0; 223 yeah->reno_count = max(yeah->reno_count>>1, 2U); 224 225 return tp->snd_cwnd - reduction; 226 } 227 228 static struct tcp_congestion_ops tcp_yeah __read_mostly = { 229 .init = tcp_yeah_init, 230 .ssthresh = tcp_yeah_ssthresh, 231 .cong_avoid = tcp_yeah_cong_avoid, 232 .set_state = tcp_vegas_state, 233 .cwnd_event = tcp_vegas_cwnd_event, 234 .get_info = tcp_vegas_get_info, 235 .pkts_acked = tcp_yeah_pkts_acked, 236 237 .owner = THIS_MODULE, 238 .name = "yeah", 239 }; 240 241 static int __init tcp_yeah_register(void) 242 { 243 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); 244 tcp_register_congestion_control(&tcp_yeah); 245 return 0; 246 } 247 248 static void __exit tcp_yeah_unregister(void) 249 { 250 tcp_unregister_congestion_control(&tcp_yeah); 251 } 252 253 module_init(tcp_yeah_register); 254 module_exit(tcp_yeah_unregister); 255 256 MODULE_AUTHOR("Angelo P. Castellani"); 257 MODULE_LICENSE("GPL"); 258 MODULE_DESCRIPTION("YeAH TCP"); 259