net/ipv4/tcp_yeah.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *
   4  *   YeAH TCP
   5  *
   6  * For further details look at:
   7  *   https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
   8  *
   9  */
  10 #include <linux/mm.h>
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/inet_diag.h>
  14
  15 #include <net/tcp.h>
  16
  17 #include "tcp_vegas.h"
  18
  19 #define TCP_YEAH_ALPHA       80 /* number of packets queued at the bottleneck */
  20 #define TCP_YEAH_GAMMA        1 /* fraction of queue to be removed per rtt */
  21 #define TCP_YEAH_DELTA        3 /* log minimum fraction of cwnd to be removed on loss */
  22 #define TCP_YEAH_EPSILON      1 /* log maximum fraction to be removed on early decongestion */
  23 #define TCP_YEAH_PHY          8 /* maximum delta from base */
  24 #define TCP_YEAH_RHO         16 /* minimum number of consecutive rtt to consider competition on loss */
  25 #define TCP_YEAH_ZETA        50 /* minimum number of state switches to reset reno_count */
  26
  27 #define TCP_SCALABLE_AI_CNT      100U
  28
  29 /* YeAH variables */
  30 struct yeah {
  31         struct vegas vegas;     /* must be first */
  32
  33         /* YeAH */
  34         u32 lastQ;
  35         u32 doing_reno_now;
  36
  37         u32 reno_count;
  38         u32 fast_count;
  39 };
  40
  41 static void tcp_yeah_init(struct sock *sk)
  42 {
  43         struct tcp_sock *tp = tcp_sk(sk);
  44         struct yeah *yeah = inet_csk_ca(sk);
  45
  46         tcp_vegas_init(sk);
  47
  48         yeah->doing_reno_now = 0;
  49         yeah->lastQ = 0;
  50
  51         yeah->reno_count = 2;
  52
  53         /* Ensure the MD arithmetic works.  This is somewhat pedantic,
  54          * since I don't think we will see a cwnd this large. :) */
  55         tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
  56 }
  57
  58 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked)
  59 {
  60         struct tcp_sock *tp = tcp_sk(sk);
  61         struct yeah *yeah = inet_csk_ca(sk);
  62
  63         if (!tcp_is_cwnd_limited(sk))
  64                 return;
  65
  66         if (tcp_in_slow_start(tp)) {
  67                 acked = tcp_slow_start(tp, acked);
  68                 if (!acked)
  69                         goto do_vegas;
  70         }
  71
  72         if (!yeah->doing_reno_now) {
  73                 /* Scalable */
  74                 tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
  75                                   acked);
  76         } else {
  77                 /* Reno */
  78                 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
  79         }
  80
  81         /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
  82          *
  83          * These are so named because they represent the approximate values
  84          * of snd_una and snd_nxt at the beginning of the current RTT. More
  85          * precisely, they represent the amount of data sent during the RTT.
  86          * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
  87          * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
  88          * bytes of data have been ACKed during the course of the RTT, giving
  89          * an "actual" rate of:
  90          *
  91          *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
  92          *
  93          * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
  94          * because delayed ACKs can cover more than one segment, so they
  95          * don't line up yeahly with the boundaries of RTTs.
  96          *
  97          * Another unfortunate fact of life is that delayed ACKs delay the
  98          * advance of the left edge of our send window, so that the number
  99          * of bytes we send in an RTT is often less than our cwnd will allow.
 100          * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
 101          */
 102 do_vegas:
 103         if (after(ack, yeah->vegas.beg_snd_nxt)) {
 104                 /* We do the Vegas calculations only if we got enough RTT
 105                  * samples that we can be reasonably sure that we got
 106                  * at least one RTT sample that wasn't from a delayed ACK.
 107                  * If we only had 2 samples total,
 108                  * then that means we're getting only 1 ACK per RTT, which
 109                  * means they're almost certainly delayed ACKs.
 110                  * If  we have 3 samples, we should be OK.
 111                  */
 112
 113                 if (yeah->vegas.cntRTT > 2) {
 114                         u32 rtt, queue;
 115                         u64 bw;
 116
 117                         /* We have enough RTT samples, so, using the Vegas
 118                          * algorithm, we determine if we should increase or
 119                          * decrease cwnd, and by how much.
 120                          */
 121
 122                         /* Pluck out the RTT we are using for the Vegas
 123                          * calculations. This is the min RTT seen during the
 124                          * last RTT. Taking the min filters out the effects
 125                          * of delayed ACKs, at the cost of noticing congestion
 126                          * a bit later.
 127                          */
 128                         rtt = yeah->vegas.minRTT;
 129
 130                         /* Compute excess number of packets above bandwidth
 131                          * Avoid doing full 64 bit divide.
 132                          */
 133                         bw = tp->snd_cwnd;
 134                         bw *= rtt - yeah->vegas.baseRTT;
 135                         do_div(bw, rtt);
 136                         queue = bw;
 137
 138                         if (queue > TCP_YEAH_ALPHA ||
 139                             rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
 140                                 if (queue > TCP_YEAH_ALPHA &&
 141                                     tp->snd_cwnd > yeah->reno_count) {
 142                                         u32 reduction = min(queue / TCP_YEAH_GAMMA ,
 143                                                             tp->snd_cwnd >> TCP_YEAH_EPSILON);
 144
 145                                         tp->snd_cwnd -= reduction;
 146
 147                                         tp->snd_cwnd = max(tp->snd_cwnd,
 148                                                            yeah->reno_count);
 149
 150                                         tp->snd_ssthresh = tp->snd_cwnd;
 151                                 }
 152
 153                                 if (yeah->reno_count <= 2)
 154                                         yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
 155                                 else
 156                                         yeah->reno_count++;
 157
 158                                 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
 159                                                            0xffffffU);
 160                         } else {
 161                                 yeah->fast_count++;
 162
 163                                 if (yeah->fast_count > TCP_YEAH_ZETA) {
 164                                         yeah->reno_count = 2;
 165                                         yeah->fast_count = 0;
 166                                 }
 167
 168                                 yeah->doing_reno_now = 0;
 169                         }
 170
 171                         yeah->lastQ = queue;
 172                 }
 173
 174                 /* Save the extent of the current window so we can use this
 175                  * at the end of the next RTT.
 176                  */
 177                 yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
 178                 yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
 179                 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
 180
 181                 /* Wipe the slate clean for the next RTT. */
 182                 yeah->vegas.cntRTT = 0;
 183                 yeah->vegas.minRTT = 0x7fffffff;
 184         }
 185 }
 186
 187 static u32 tcp_yeah_ssthresh(struct sock *sk)
 188 {
 189         const struct tcp_sock *tp = tcp_sk(sk);
 190         struct yeah *yeah = inet_csk_ca(sk);
 191         u32 reduction;
 192
 193         if (yeah->doing_reno_now < TCP_YEAH_RHO) {
 194                 reduction = yeah->lastQ;
 195
 196                 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
 197
 198                 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
 199         } else
 200                 reduction = max(tp->snd_cwnd>>1, 2U);
 201
 202         yeah->fast_count = 0;
 203         yeah->reno_count = max(yeah->reno_count>>1, 2U);
 204
 205         return max_t(int, tp->snd_cwnd - reduction, 2);
 206 }
 207
 208 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
 209         .init           = tcp_yeah_init,
 210         .ssthresh       = tcp_yeah_ssthresh,
 211         .undo_cwnd      = tcp_reno_undo_cwnd,
 212         .cong_avoid     = tcp_yeah_cong_avoid,
 213         .set_state      = tcp_vegas_state,
 214         .cwnd_event     = tcp_vegas_cwnd_event,
 215         .get_info       = tcp_vegas_get_info,
 216         .pkts_acked     = tcp_vegas_pkts_acked,
 217
 218         .owner          = THIS_MODULE,
 219         .name           = "yeah",
 220 };
 221
 222 static int __init tcp_yeah_register(void)
 223 {
 224         BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
 225         tcp_register_congestion_control(&tcp_yeah);
 226         return 0;
 227 }
 228
 229 static void __exit tcp_yeah_unregister(void)
 230 {
 231         tcp_unregister_congestion_control(&tcp_yeah);
 232 }
 233
 234 module_init(tcp_yeah_register);
 235 module_exit(tcp_yeah_unregister);
 236
 237 MODULE_AUTHOR("Angelo P. Castellani");
 238 MODULE_LICENSE("GPL");
 239 MODULE_DESCRIPTION("YeAH TCP");