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         u32 loss_cwnd;
  41 };
  42
  43 static void tcp_yeah_init(struct sock *sk)
  44 {
  45         struct tcp_sock *tp = tcp_sk(sk);
  46         struct yeah *yeah = inet_csk_ca(sk);
  47
  48         tcp_vegas_init(sk);
  49
  50         yeah->doing_reno_now = 0;
  51         yeah->lastQ = 0;
  52
  53         yeah->reno_count = 2;
  54
  55         /* Ensure the MD arithmetic works.  This is somewhat pedantic,
  56          * since I don't think we will see a cwnd this large. :) */
  57         tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
  58 }
  59
  60 static void tcp_yeah_pkts_acked(struct sock *sk,
  61                                 const struct ack_sample *sample)
  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 = sample->pkts_acked;
  68
  69         tcp_vegas_pkts_acked(sk, sample);
  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 (tcp_in_slow_start(tp))
  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, 1);
  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                 /* We do the Vegas calculations only if we got enough RTT
 124                  * samples that we can be reasonably sure that we got
 125                  * at least one RTT sample that wasn't from a delayed ACK.
 126                  * If we only had 2 samples total,
 127                  * then that means we're getting only 1 ACK per RTT, which
 128                  * means they're almost certainly delayed ACKs.
 129                  * If  we have 3 samples, we should be OK.
 130                  */
 131
 132                 if (yeah->vegas.cntRTT > 2) {
 133                         u32 rtt, queue;
 134                         u64 bw;
 135
 136                         /* We have enough RTT samples, so, using the Vegas
 137                          * algorithm, we determine if we should increase or
 138                          * decrease cwnd, and by how much.
 139                          */
 140
 141                         /* Pluck out the RTT we are using for the Vegas
 142                          * calculations. This is the min RTT seen during the
 143                          * last RTT. Taking the min filters out the effects
 144                          * of delayed ACKs, at the cost of noticing congestion
 145                          * a bit later.
 146                          */
 147                         rtt = yeah->vegas.minRTT;
 148
 149                         /* Compute excess number of packets above bandwidth
 150                          * Avoid doing full 64 bit divide.
 151                          */
 152                         bw = tp->snd_cwnd;
 153                         bw *= rtt - yeah->vegas.baseRTT;
 154                         do_div(bw, rtt);
 155                         queue = bw;
 156
 157                         if (queue > TCP_YEAH_ALPHA ||
 158                             rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
 159                                 if (queue > TCP_YEAH_ALPHA &&
 160                                     tp->snd_cwnd > yeah->reno_count) {
 161                                         u32 reduction = min(queue / TCP_YEAH_GAMMA ,
 162                                                             tp->snd_cwnd >> TCP_YEAH_EPSILON);
 163
 164                                         tp->snd_cwnd -= reduction;
 165
 166                                         tp->snd_cwnd = max(tp->snd_cwnd,
 167                                                            yeah->reno_count);
 168
 169                                         tp->snd_ssthresh = tp->snd_cwnd;
 170                                 }
 171
 172                                 if (yeah->reno_count <= 2)
 173                                         yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
 174                                 else
 175                                         yeah->reno_count++;
 176
 177                                 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
 178                                                            0xffffffU);
 179                         } else {
 180                                 yeah->fast_count++;
 181
 182                                 if (yeah->fast_count > TCP_YEAH_ZETA) {
 183                                         yeah->reno_count = 2;
 184                                         yeah->fast_count = 0;
 185                                 }
 186
 187                                 yeah->doing_reno_now = 0;
 188                         }
 189
 190                         yeah->lastQ = queue;
 191                 }
 192
 193                 /* Save the extent of the current window so we can use this
 194                  * at the end of the next RTT.
 195                  */
 196                 yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
 197                 yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
 198                 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
 199
 200                 /* Wipe the slate clean for the next RTT. */
 201                 yeah->vegas.cntRTT = 0;
 202                 yeah->vegas.minRTT = 0x7fffffff;
 203         }
 204 }
 205
 206 static u32 tcp_yeah_ssthresh(struct sock *sk)
 207 {
 208         const struct tcp_sock *tp = tcp_sk(sk);
 209         struct yeah *yeah = inet_csk_ca(sk);
 210         u32 reduction;
 211
 212         if (yeah->doing_reno_now < TCP_YEAH_RHO) {
 213                 reduction = yeah->lastQ;
 214
 215                 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
 216
 217                 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
 218         } else
 219                 reduction = max(tp->snd_cwnd>>1, 2U);
 220
 221         yeah->fast_count = 0;
 222         yeah->reno_count = max(yeah->reno_count>>1, 2U);
 223         yeah->loss_cwnd = tp->snd_cwnd;
 224
 225         return max_t(int, tp->snd_cwnd - reduction, 2);
 226 }
 227
 228 static u32 tcp_yeah_cwnd_undo(struct sock *sk)
 229 {
 230         const struct yeah *yeah = inet_csk_ca(sk);
 231
 232         return max(tcp_sk(sk)->snd_cwnd, yeah->loss_cwnd);
 233 }
 234
 235 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
 236         .init           = tcp_yeah_init,
 237         .ssthresh       = tcp_yeah_ssthresh,
 238         .undo_cwnd      = tcp_yeah_cwnd_undo,
 239         .cong_avoid     = tcp_yeah_cong_avoid,
 240         .set_state      = tcp_vegas_state,
 241         .cwnd_event     = tcp_vegas_cwnd_event,
 242         .get_info       = tcp_vegas_get_info,
 243         .pkts_acked     = tcp_yeah_pkts_acked,
 244
 245         .owner          = THIS_MODULE,
 246         .name           = "yeah",
 247 };
 248
 249 static int __init tcp_yeah_register(void)
 250 {
 251         BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
 252         tcp_register_congestion_control(&tcp_yeah);
 253         return 0;
 254 }
 255
 256 static void __exit tcp_yeah_unregister(void)
 257 {
 258         tcp_unregister_congestion_control(&tcp_yeah);
 259 }
 260
 261 module_init(tcp_yeah_register);
 262 module_exit(tcp_yeah_unregister);
 263
 264 MODULE_AUTHOR("Angelo P. Castellani");
 265 MODULE_LICENSE("GPL");
 266 MODULE_DESCRIPTION("YeAH TCP");