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, u32 pkts_acked, s32 rtt_us) 60 { 61 const struct inet_connection_sock *icsk = inet_csk(sk); 62 struct yeah *yeah = inet_csk_ca(sk); 63 64 if (icsk->icsk_ca_state == TCP_CA_Open) 65 yeah->pkts_acked = pkts_acked; 66 67 tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us); 68 } 69 70 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked) 71 { 72 struct tcp_sock *tp = tcp_sk(sk); 73 struct yeah *yeah = inet_csk_ca(sk); 74 75 if (!tcp_is_cwnd_limited(sk)) 76 return; 77 78 if (tp->snd_cwnd <= tp->snd_ssthresh) 79 tcp_slow_start(tp, acked); 80 81 else if (!yeah->doing_reno_now) { 82 /* Scalable */ 83 84 tp->snd_cwnd_cnt += yeah->pkts_acked; 85 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) { 86 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 87 tp->snd_cwnd++; 88 tp->snd_cwnd_cnt = 0; 89 } 90 91 yeah->pkts_acked = 1; 92 93 } else { 94 /* Reno */ 95 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); 96 } 97 98 /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. 99 * 100 * These are so named because they represent the approximate values 101 * of snd_una and snd_nxt at the beginning of the current RTT. More 102 * precisely, they represent the amount of data sent during the RTT. 103 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, 104 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding 105 * bytes of data have been ACKed during the course of the RTT, giving 106 * an "actual" rate of: 107 * 108 * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) 109 * 110 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, 111 * because delayed ACKs can cover more than one segment, so they 112 * don't line up yeahly with the boundaries of RTTs. 113 * 114 * Another unfortunate fact of life is that delayed ACKs delay the 115 * advance of the left edge of our send window, so that the number 116 * of bytes we send in an RTT is often less than our cwnd will allow. 117 * So we keep track of our cwnd separately, in v_beg_snd_cwnd. 118 */ 119 120 if (after(ack, yeah->vegas.beg_snd_nxt)) { 121 /* We do the Vegas calculations only if we got enough RTT 122 * samples that we can be reasonably sure that we got 123 * at least one RTT sample that wasn't from a delayed ACK. 124 * If we only had 2 samples total, 125 * then that means we're getting only 1 ACK per RTT, which 126 * means they're almost certainly delayed ACKs. 127 * If we have 3 samples, we should be OK. 128 */ 129 130 if (yeah->vegas.cntRTT > 2) { 131 u32 rtt, queue; 132 u64 bw; 133 134 /* We have enough RTT samples, so, using the Vegas 135 * algorithm, we determine if we should increase or 136 * decrease cwnd, and by how much. 137 */ 138 139 /* Pluck out the RTT we are using for the Vegas 140 * calculations. This is the min RTT seen during the 141 * last RTT. Taking the min filters out the effects 142 * of delayed ACKs, at the cost of noticing congestion 143 * a bit later. 144 */ 145 rtt = yeah->vegas.minRTT; 146 147 /* Compute excess number of packets above bandwidth 148 * Avoid doing full 64 bit divide. 149 */ 150 bw = tp->snd_cwnd; 151 bw *= rtt - yeah->vegas.baseRTT; 152 do_div(bw, rtt); 153 queue = bw; 154 155 if (queue > TCP_YEAH_ALPHA || 156 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { 157 if (queue > TCP_YEAH_ALPHA && 158 tp->snd_cwnd > yeah->reno_count) { 159 u32 reduction = min(queue / TCP_YEAH_GAMMA , 160 tp->snd_cwnd >> TCP_YEAH_EPSILON); 161 162 tp->snd_cwnd -= reduction; 163 164 tp->snd_cwnd = max(tp->snd_cwnd, 165 yeah->reno_count); 166 167 tp->snd_ssthresh = tp->snd_cwnd; 168 } 169 170 if (yeah->reno_count <= 2) 171 yeah->reno_count = max(tp->snd_cwnd>>1, 2U); 172 else 173 yeah->reno_count++; 174 175 yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 176 0xffffffU); 177 } else { 178 yeah->fast_count++; 179 180 if (yeah->fast_count > TCP_YEAH_ZETA) { 181 yeah->reno_count = 2; 182 yeah->fast_count = 0; 183 } 184 185 yeah->doing_reno_now = 0; 186 } 187 188 yeah->lastQ = queue; 189 } 190 191 /* Save the extent of the current window so we can use this 192 * at the end of the next RTT. 193 */ 194 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; 195 yeah->vegas.beg_snd_nxt = tp->snd_nxt; 196 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; 197 198 /* Wipe the slate clean for the next RTT. */ 199 yeah->vegas.cntRTT = 0; 200 yeah->vegas.minRTT = 0x7fffffff; 201 } 202 } 203 204 static u32 tcp_yeah_ssthresh(struct sock *sk) 205 { 206 const struct tcp_sock *tp = tcp_sk(sk); 207 struct yeah *yeah = inet_csk_ca(sk); 208 u32 reduction; 209 210 if (yeah->doing_reno_now < TCP_YEAH_RHO) { 211 reduction = yeah->lastQ; 212 213 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); 214 215 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); 216 } else 217 reduction = max(tp->snd_cwnd>>1, 2U); 218 219 yeah->fast_count = 0; 220 yeah->reno_count = max(yeah->reno_count>>1, 2U); 221 222 return max_t(int, tp->snd_cwnd - reduction, 2); 223 } 224 225 static struct tcp_congestion_ops tcp_yeah __read_mostly = { 226 .init = tcp_yeah_init, 227 .ssthresh = tcp_yeah_ssthresh, 228 .cong_avoid = tcp_yeah_cong_avoid, 229 .set_state = tcp_vegas_state, 230 .cwnd_event = tcp_vegas_cwnd_event, 231 .get_info = tcp_vegas_get_info, 232 .pkts_acked = tcp_yeah_pkts_acked, 233 234 .owner = THIS_MODULE, 235 .name = "yeah", 236 }; 237 238 static int __init tcp_yeah_register(void) 239 { 240 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); 241 tcp_register_congestion_control(&tcp_yeah); 242 return 0; 243 } 244 245 static void __exit tcp_yeah_unregister(void) 246 { 247 tcp_unregister_congestion_control(&tcp_yeah); 248 } 249 250 module_init(tcp_yeah_register); 251 module_exit(tcp_yeah_unregister); 252 253 MODULE_AUTHOR("Angelo P. Castellani"); 254 MODULE_LICENSE("GPL"); 255 MODULE_DESCRIPTION("YeAH TCP"); 256