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   1 /*
   2  *
   3  *   YeAH TCP
   4  *
   5  * For further details look at:
   6  *    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
   7  *
   8  */
   9
  10 #include "tcp_yeah.h"
  11
  12 /* Default values of the Vegas variables, in fixed-point representation
  13  * with V_PARAM_SHIFT bits to the right of the binary point.
  14  */
  15 #define V_PARAM_SHIFT 1
  16
  17 #define TCP_YEAH_ALPHA       80 //lin number of packets queued at the bottleneck
  18 #define TCP_YEAH_GAMMA        1 //lin fraction of queue to be removed per rtt
  19 #define TCP_YEAH_DELTA        3 //log minimum fraction of cwnd to be removed on loss
  20 #define TCP_YEAH_EPSILON      1 //log maximum fraction to be removed on early decongestion
  21 #define TCP_YEAH_PHY          8 //lin maximum delta from base
  22 #define TCP_YEAH_RHO         16 //lin minumum number of consecutive rtt to consider competition on loss
  23 #define TCP_YEAH_ZETA        50 //lin minimum number of state switchs to reset reno_count
  24
  25 #define TCP_SCALABLE_AI_CNT      100U
  26
  27 /* YeAH variables */
  28 struct yeah {
  29         /* Vegas */
  30         u32     beg_snd_nxt;    /* right edge during last RTT */
  31         u32     beg_snd_una;    /* left edge  during last RTT */
  32         u32     beg_snd_cwnd;   /* saves the size of the cwnd */
  33         u8      doing_vegas_now;/* if true, do vegas for this RTT */
  34         u16     cntRTT;         /* # of RTTs measured within last RTT */
  35         u32     minRTT;         /* min of RTTs measured within last RTT (in usec) */
  36         u32     baseRTT;        /* the min of all Vegas RTT measurements seen (in usec) */
  37
  38         /* YeAH */
  39         u32 lastQ;
  40         u32 doing_reno_now;
  41
  42         u32 reno_count;
  43         u32 fast_count;
  44
  45         u32 pkts_acked;
  46 };
  47
  48 static void tcp_yeah_init(struct sock *sk)
  49 {
  50         struct tcp_sock *tp = tcp_sk(sk);
  51         struct yeah *yeah = inet_csk_ca(sk);
  52
  53         tcp_vegas_init(sk);
  54
  55         yeah->doing_reno_now = 0;
  56         yeah->lastQ = 0;
  57
  58         yeah->reno_count = 2;
  59
  60         /* Ensure the MD arithmetic works.  This is somewhat pedantic,
  61          * since I don't think we will see a cwnd this large. :) */
  62         tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
  63
  64 }
  65
  66
  67 static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked)
  68 {
  69         const struct inet_connection_sock *icsk = inet_csk(sk);
  70         struct yeah *yeah = inet_csk_ca(sk);
  71
  72         if (icsk->icsk_ca_state == TCP_CA_Open)
  73                 yeah->pkts_acked = pkts_acked;
  74 }
  75
  76 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack,
  77                                  u32 seq_rtt, u32 in_flight, int flag)
  78 {
  79         struct tcp_sock *tp = tcp_sk(sk);
  80         struct yeah *yeah = inet_csk_ca(sk);
  81
  82         if (!tcp_is_cwnd_limited(sk, in_flight))
  83                 return;
  84
  85         if (tp->snd_cwnd <= tp->snd_ssthresh) {
  86                 tcp_slow_start(tp);
  87         } else if (!yeah->doing_reno_now) {
  88                 /* Scalable */
  89
  90                 tp->snd_cwnd_cnt+=yeah->pkts_acked;
  91                 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
  92                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
  93                                 tp->snd_cwnd++;
  94                         tp->snd_cwnd_cnt = 0;
  95                 }
  96
  97                 yeah->pkts_acked = 1;
  98
  99         } else {
 100                 /* Reno */
 101
 102                 if (tp->snd_cwnd_cnt < tp->snd_cwnd)
 103                         tp->snd_cwnd_cnt++;
 104
 105                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 106                         tp->snd_cwnd++;
 107                         tp->snd_cwnd_cnt = 0;
 108                 }
 109         }
 110
 111         /* The key players are v_beg_snd_una and v_beg_snd_nxt.
 112          *
 113          * These are so named because they represent the approximate values
 114          * of snd_una and snd_nxt at the beginning of the current RTT. More
 115          * precisely, they represent the amount of data sent during the RTT.
 116          * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
 117          * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
 118          * bytes of data have been ACKed during the course of the RTT, giving
 119          * an "actual" rate of:
 120          *
 121          *     (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
 122          *
 123          * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
 124          * because delayed ACKs can cover more than one segment, so they
 125          * don't line up yeahly with the boundaries of RTTs.
 126          *
 127          * Another unfortunate fact of life is that delayed ACKs delay the
 128          * advance of the left edge of our send window, so that the number
 129          * of bytes we send in an RTT is often less than our cwnd will allow.
 130          * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
 131          */
 132
 133         if (after(ack, yeah->beg_snd_nxt)) {
 134
 135                 /* We do the Vegas calculations only if we got enough RTT
 136                  * samples that we can be reasonably sure that we got
 137                  * at least one RTT sample that wasn't from a delayed ACK.
 138                  * If we only had 2 samples total,
 139                  * then that means we're getting only 1 ACK per RTT, which
 140                  * means they're almost certainly delayed ACKs.
 141                  * If  we have 3 samples, we should be OK.
 142                  */
 143
 144                 if (yeah->cntRTT > 2) {
 145                         u32 rtt;
 146                         u32 queue, maxqueue;
 147
 148                         /* We have enough RTT samples, so, using the Vegas
 149                          * algorithm, we determine if we should increase or
 150                          * decrease cwnd, and by how much.
 151                          */
 152
 153                         /* Pluck out the RTT we are using for the Vegas
 154                          * calculations. This is the min RTT seen during the
 155                          * last RTT. Taking the min filters out the effects
 156                          * of delayed ACKs, at the cost of noticing congestion
 157                          * a bit later.
 158                          */
 159                         rtt = yeah->minRTT;
 160
 161                         queue = (u32)div64_64((u64)tp->snd_cwnd * (rtt - yeah->baseRTT), rtt);
 162
 163                         maxqueue = TCP_YEAH_ALPHA;
 164
 165                         if (queue > maxqueue ||
 166                                     rtt - yeah->baseRTT > (yeah->baseRTT / TCP_YEAH_PHY)) {
 167
 168                                 if (queue > maxqueue && tp->snd_cwnd > yeah->reno_count) {
 169                                         u32 reduction = min( queue / TCP_YEAH_GAMMA ,
 170                                                          tp->snd_cwnd >> TCP_YEAH_EPSILON );
 171
 172                                         tp->snd_cwnd -= reduction;
 173
 174                                         tp->snd_cwnd = max( tp->snd_cwnd, yeah->reno_count);
 175
 176                                         tp->snd_ssthresh = tp->snd_cwnd;
 177                         }
 178
 179                                 if (yeah->reno_count <= 2)
 180                                         yeah->reno_count = max( tp->snd_cwnd>>1, 2U);
 181                                 else
 182                                         yeah->reno_count++;
 183
 184                                 yeah->doing_reno_now =
 185                                                    min_t( u32, yeah->doing_reno_now + 1 , 0xffffff);
 186
 187                         } else {
 188                                 yeah->fast_count++;
 189
 190                                 if (yeah->fast_count > TCP_YEAH_ZETA) {
 191                                         yeah->reno_count = 2;
 192                                         yeah->fast_count = 0;
 193                                 }
 194
 195                                 yeah->doing_reno_now = 0;
 196                         }
 197
 198                         yeah->lastQ = queue;
 199
 200                 }
 201
 202                 /* Save the extent of the current window so we can use this
 203                  * at the end of the next RTT.
 204                  */
 205                 yeah->beg_snd_una  = yeah->beg_snd_nxt;
 206                 yeah->beg_snd_nxt  = tp->snd_nxt;
 207                 yeah->beg_snd_cwnd = tp->snd_cwnd;
 208
 209                 /* Wipe the slate clean for the next RTT. */
 210                 yeah->cntRTT = 0;
 211                 yeah->minRTT = 0x7fffffff;
 212         }
 213 }
 214
 215 static u32 tcp_yeah_ssthresh(struct sock *sk) {
 216         const struct tcp_sock *tp = tcp_sk(sk);
 217         struct yeah *yeah = inet_csk_ca(sk);
 218         u32 reduction;
 219
 220         if (yeah->doing_reno_now < TCP_YEAH_RHO) {
 221                 reduction = yeah->lastQ;
 222
 223                 reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );
 224
 225                 reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
 226         } else
 227                 reduction = max(tp->snd_cwnd>>1,2U);
 228
 229         yeah->fast_count = 0;
 230         yeah->reno_count = max(yeah->reno_count>>1, 2U);
 231
 232         return tp->snd_cwnd - reduction;
 233 }
 234
 235 static struct tcp_congestion_ops tcp_yeah = {
 236         .init           = tcp_yeah_init,
 237         .ssthresh       = tcp_yeah_ssthresh,
 238         .cong_avoid     = tcp_yeah_cong_avoid,
 239         .min_cwnd       = tcp_reno_min_cwnd,
 240         .rtt_sample     = tcp_vegas_rtt_calc,
 241         .set_state      = tcp_vegas_state,
 242         .cwnd_event     = tcp_vegas_cwnd_event,
 243         .get_info       = tcp_vegas_get_info,
 244         .pkts_acked     = tcp_yeah_pkts_acked,
 245
 246         .owner          = THIS_MODULE,
 247         .name           = "yeah",
 248 };
 249
 250 static int __init tcp_yeah_register(void)
 251 {
 252         BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
 253         tcp_register_congestion_control(&tcp_yeah);
 254         return 0;
 255 }
 256
 257 static void __exit tcp_yeah_unregister(void)
 258 {
 259         tcp_unregister_congestion_control(&tcp_yeah);
 260 }
 261
 262 module_init(tcp_yeah_register);
 263 module_exit(tcp_yeah_unregister);
 264
 265 MODULE_AUTHOR("Angelo P. Castellani");
 266 MODULE_LICENSE("GPL");
 267 MODULE_DESCRIPTION("YeAH TCP");