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 static void tcp_yeah_pkts_acked(struct sock *sk, 60 const struct ack_sample *sample) 61 { 62 const struct inet_connection_sock *icsk = inet_csk(sk); 63 struct yeah *yeah = inet_csk_ca(sk); 64 65 if (icsk->icsk_ca_state == TCP_CA_Open) 66 yeah->pkts_acked = sample->pkts_acked; 67 68 tcp_vegas_pkts_acked(sk, sample); 69 } 70 71 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked) 72 { 73 struct tcp_sock *tp = tcp_sk(sk); 74 struct yeah *yeah = inet_csk_ca(sk); 75 76 if (!tcp_is_cwnd_limited(sk)) 77 return; 78 79 if (tcp_in_slow_start(tp)) 80 tcp_slow_start(tp, acked); 81 82 else if (!yeah->doing_reno_now) { 83 /* Scalable */ 84 85 tp->snd_cwnd_cnt += yeah->pkts_acked; 86 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) { 87 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 88 tp->snd_cwnd++; 89 tp->snd_cwnd_cnt = 0; 90 } 91 92 yeah->pkts_acked = 1; 93 94 } else { 95 /* Reno */ 96 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 97 } 98 99 /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. 100 * 101 * These are so named because they represent the approximate values 102 * of snd_una and snd_nxt at the beginning of the current RTT. More 103 * precisely, they represent the amount of data sent during the RTT. 104 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, 105 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding 106 * bytes of data have been ACKed during the course of the RTT, giving 107 * an "actual" rate of: 108 * 109 * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) 110 * 111 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, 112 * because delayed ACKs can cover more than one segment, so they 113 * don't line up yeahly with the boundaries of RTTs. 114 * 115 * Another unfortunate fact of life is that delayed ACKs delay the 116 * advance of the left edge of our send window, so that the number 117 * of bytes we send in an RTT is often less than our cwnd will allow. 118 * So we keep track of our cwnd separately, in v_beg_snd_cwnd. 119 */ 120 121 if (after(ack, yeah->vegas.beg_snd_nxt)) { 122 /* We do the Vegas calculations only if we got enough RTT 123 * samples that we can be reasonably sure that we got 124 * at least one RTT sample that wasn't from a delayed ACK. 125 * If we only had 2 samples total, 126 * then that means we're getting only 1 ACK per RTT, which 127 * means they're almost certainly delayed ACKs. 128 * If we have 3 samples, we should be OK. 129 */ 130 131 if (yeah->vegas.cntRTT > 2) { 132 u32 rtt, queue; 133 u64 bw; 134 135 /* We have enough RTT samples, so, using the Vegas 136 * algorithm, we determine if we should increase or 137 * decrease cwnd, and by how much. 138 */ 139 140 /* Pluck out the RTT we are using for the Vegas 141 * calculations. This is the min RTT seen during the 142 * last RTT. Taking the min filters out the effects 143 * of delayed ACKs, at the cost of noticing congestion 144 * a bit later. 145 */ 146 rtt = yeah->vegas.minRTT; 147 148 /* Compute excess number of packets above bandwidth 149 * Avoid doing full 64 bit divide. 150 */ 151 bw = tp->snd_cwnd; 152 bw *= rtt - yeah->vegas.baseRTT; 153 do_div(bw, rtt); 154 queue = bw; 155 156 if (queue > TCP_YEAH_ALPHA || 157 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { 158 if (queue > TCP_YEAH_ALPHA && 159 tp->snd_cwnd > yeah->reno_count) { 160 u32 reduction = min(queue / TCP_YEAH_GAMMA , 161 tp->snd_cwnd >> TCP_YEAH_EPSILON); 162 163 tp->snd_cwnd -= reduction; 164 165 tp->snd_cwnd = max(tp->snd_cwnd, 166 yeah->reno_count); 167 168 tp->snd_ssthresh = tp->snd_cwnd; 169 } 170 171 if (yeah->reno_count <= 2) 172 yeah->reno_count = max(tp->snd_cwnd>>1, 2U); 173 else 174 yeah->reno_count++; 175 176 yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 177 0xffffffU); 178 } else { 179 yeah->fast_count++; 180 181 if (yeah->fast_count > TCP_YEAH_ZETA) { 182 yeah->reno_count = 2; 183 yeah->fast_count = 0; 184 } 185 186 yeah->doing_reno_now = 0; 187 } 188 189 yeah->lastQ = queue; 190 } 191 192 /* Save the extent of the current window so we can use this 193 * at the end of the next RTT. 194 */ 195 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; 196 yeah->vegas.beg_snd_nxt = tp->snd_nxt; 197 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; 198 199 /* Wipe the slate clean for the next RTT. */ 200 yeah->vegas.cntRTT = 0; 201 yeah->vegas.minRTT = 0x7fffffff; 202 } 203 } 204 205 static u32 tcp_yeah_ssthresh(struct sock *sk) 206 { 207 const struct tcp_sock *tp = tcp_sk(sk); 208 struct yeah *yeah = inet_csk_ca(sk); 209 u32 reduction; 210 211 if (yeah->doing_reno_now < TCP_YEAH_RHO) { 212 reduction = yeah->lastQ; 213 214 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); 215 216 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); 217 } else 218 reduction = max(tp->snd_cwnd>>1, 2U); 219 220 yeah->fast_count = 0; 221 yeah->reno_count = max(yeah->reno_count>>1, 2U); 222 223 return max_t(int, tp->snd_cwnd - reduction, 2); 224 } 225 226 static struct tcp_congestion_ops tcp_yeah __read_mostly = { 227 .init = tcp_yeah_init, 228 .ssthresh = tcp_yeah_ssthresh, 229 .cong_avoid = tcp_yeah_cong_avoid, 230 .set_state = tcp_vegas_state, 231 .cwnd_event = tcp_vegas_cwnd_event, 232 .get_info = tcp_vegas_get_info, 233 .pkts_acked = tcp_yeah_pkts_acked, 234 235 .owner = THIS_MODULE, 236 .name = "yeah", 237 }; 238 239 static int __init tcp_yeah_register(void) 240 { 241 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); 242 tcp_register_congestion_control(&tcp_yeah); 243 return 0; 244 } 245 246 static void __exit tcp_yeah_unregister(void) 247 { 248 tcp_unregister_congestion_control(&tcp_yeah); 249 } 250 251 module_init(tcp_yeah_register); 252 module_exit(tcp_yeah_unregister); 253 254 MODULE_AUTHOR("Angelo P. Castellani"); 255 MODULE_LICENSE("GPL"); 256 MODULE_DESCRIPTION("YeAH TCP"); 257