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
  60
  61 static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us)
  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 = pkts_acked;
  68
  69         tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us);
  70 }
  71
  72 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked,
  73                                 u32 in_flight)
  74 {
  75         struct tcp_sock *tp = tcp_sk(sk);
  76         struct yeah *yeah = inet_csk_ca(sk);
  77
  78         if (!tcp_is_cwnd_limited(sk, in_flight))
  79                 return;
  80
  81         if (tp->snd_cwnd <= tp->snd_ssthresh)
  82                 tcp_slow_start(tp, acked);
  83
  84         else if (!yeah->doing_reno_now) {
  85                 /* Scalable */
  86
  87                 tp->snd_cwnd_cnt += yeah->pkts_acked;
  88                 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
  89                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
  90                                 tp->snd_cwnd++;
  91                         tp->snd_cwnd_cnt = 0;
  92                 }
  93
  94                 yeah->pkts_acked = 1;
  95
  96         } else {
  97                 /* Reno */
  98                 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
  99         }
 100
 101         /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
 102          *
 103          * These are so named because they represent the approximate values
 104          * of snd_una and snd_nxt at the beginning of the current RTT. More
 105          * precisely, they represent the amount of data sent during the RTT.
 106          * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
 107          * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
 108          * bytes of data have been ACKed during the course of the RTT, giving
 109          * an "actual" rate of:
 110          *
 111          *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
 112          *
 113          * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
 114          * because delayed ACKs can cover more than one segment, so they
 115          * don't line up yeahly with the boundaries of RTTs.
 116          *
 117          * Another unfortunate fact of life is that delayed ACKs delay the
 118          * advance of the left edge of our send window, so that the number
 119          * of bytes we send in an RTT is often less than our cwnd will allow.
 120          * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
 121          */
 122
 123         if (after(ack, yeah->vegas.beg_snd_nxt)) {
 124
 125                 /* We do the Vegas calculations only if we got enough RTT
 126                  * samples that we can be reasonably sure that we got
 127                  * at least one RTT sample that wasn't from a delayed ACK.
 128                  * If we only had 2 samples total,
 129                  * then that means we're getting only 1 ACK per RTT, which
 130                  * means they're almost certainly delayed ACKs.
 131                  * If  we have 3 samples, we should be OK.
 132                  */
 133
 134                 if (yeah->vegas.cntRTT > 2) {
 135                         u32 rtt, queue;
 136                         u64 bw;
 137
 138                         /* We have enough RTT samples, so, using the Vegas
 139                          * algorithm, we determine if we should increase or
 140                          * decrease cwnd, and by how much.
 141                          */
 142
 143                         /* Pluck out the RTT we are using for the Vegas
 144                          * calculations. This is the min RTT seen during the
 145                          * last RTT. Taking the min filters out the effects
 146                          * of delayed ACKs, at the cost of noticing congestion
 147                          * a bit later.
 148                          */
 149                         rtt = yeah->vegas.minRTT;
 150
 151                         /* Compute excess number of packets above bandwidth
 152                          * Avoid doing full 64 bit divide.
 153                          */
 154                         bw = tp->snd_cwnd;
 155                         bw *= rtt - yeah->vegas.baseRTT;
 156                         do_div(bw, rtt);
 157                         queue = bw;
 158
 159                         if (queue > TCP_YEAH_ALPHA ||
 160                             rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
 161                                 if (queue > TCP_YEAH_ALPHA &&
 162                                     tp->snd_cwnd > yeah->reno_count) {
 163                                         u32 reduction = min(queue / TCP_YEAH_GAMMA ,
 164                                                             tp->snd_cwnd >> TCP_YEAH_EPSILON);
 165
 166                                         tp->snd_cwnd -= reduction;
 167
 168                                         tp->snd_cwnd = max(tp->snd_cwnd,
 169                                                            yeah->reno_count);
 170
 171                                         tp->snd_ssthresh = tp->snd_cwnd;
 172                                 }
 173
 174                                 if (yeah->reno_count <= 2)
 175                                         yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
 176                                 else
 177                                         yeah->reno_count++;
 178
 179                                 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
 180                                                            0xffffffU);
 181                         } else {
 182                                 yeah->fast_count++;
 183
 184                                 if (yeah->fast_count > TCP_YEAH_ZETA) {
 185                                         yeah->reno_count = 2;
 186                                         yeah->fast_count = 0;
 187                                 }
 188
 189                                 yeah->doing_reno_now = 0;
 190                         }
 191
 192                         yeah->lastQ = queue;
 193
 194                 }
 195
 196                 /* Save the extent of the current window so we can use this
 197                  * at the end of the next RTT.
 198                  */
 199                 yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
 200                 yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
 201                 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
 202
 203                 /* Wipe the slate clean for the next RTT. */
 204                 yeah->vegas.cntRTT = 0;
 205                 yeah->vegas.minRTT = 0x7fffffff;
 206         }
 207 }
 208
 209 static u32 tcp_yeah_ssthresh(struct sock *sk) {
 210         const struct tcp_sock *tp = tcp_sk(sk);
 211         struct yeah *yeah = inet_csk_ca(sk);
 212         u32 reduction;
 213
 214         if (yeah->doing_reno_now < TCP_YEAH_RHO) {
 215                 reduction = yeah->lastQ;
 216
 217                 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
 218
 219                 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
 220         } else
 221                 reduction = max(tp->snd_cwnd>>1, 2U);
 222
 223         yeah->fast_count = 0;
 224         yeah->reno_count = max(yeah->reno_count>>1, 2U);
 225
 226         return tp->snd_cwnd - reduction;
 227 }
 228
 229 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
 230         .flags          = TCP_CONG_RTT_STAMP,
 231         .init           = tcp_yeah_init,
 232         .ssthresh       = tcp_yeah_ssthresh,
 233         .cong_avoid     = tcp_yeah_cong_avoid,
 234         .min_cwnd       = tcp_reno_min_cwnd,
 235         .set_state      = tcp_vegas_state,
 236         .cwnd_event     = tcp_vegas_cwnd_event,
 237         .get_info       = tcp_vegas_get_info,
 238         .pkts_acked     = tcp_yeah_pkts_acked,
 239
 240         .owner          = THIS_MODULE,
 241         .name           = "yeah",
 242 };
 243
 244 static int __init tcp_yeah_register(void)
 245 {
 246         BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
 247         tcp_register_congestion_control(&tcp_yeah);
 248         return 0;
 249 }
 250
 251 static void __exit tcp_yeah_unregister(void)
 252 {
 253         tcp_unregister_congestion_control(&tcp_yeah);
 254 }
 255
 256 module_init(tcp_yeah_register);
 257 module_exit(tcp_yeah_unregister);
 258
 259 MODULE_AUTHOR("Angelo P. Castellani");
 260 MODULE_LICENSE("GPL");
 261 MODULE_DESCRIPTION("YeAH TCP");