net/ipv4/tcp_yeah.c

   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");