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, 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");