net/ipv4/tcp_highspeed.c

   1 /*
   2  * Sally Floyd's High Speed TCP (RFC 3649) congestion control
   3  *
   4  * See http://www.icir.org/floyd/hstcp.html
   5  *
   6  * John Heffner <jheffner@psc.edu>
   7  */
   8
   9 #include <linux/module.h>
  10 #include <net/tcp.h>
  11
  12
  13 /* From AIMD tables from RFC 3649 appendix B,
  14  * with fixed-point MD scaled <<8.
  15  */
  16 static const struct hstcp_aimd_val {
  17         unsigned int cwnd;
  18         unsigned int md;
  19 } hstcp_aimd_vals[] = {
  20  {     38,  128, /*  0.50 */ },
  21  {    118,  112, /*  0.44 */ },
  22  {    221,  104, /*  0.41 */ },
  23  {    347,   98, /*  0.38 */ },
  24  {    495,   93, /*  0.37 */ },
  25  {    663,   89, /*  0.35 */ },
  26  {    851,   86, /*  0.34 */ },
  27  {   1058,   83, /*  0.33 */ },
  28  {   1284,   81, /*  0.32 */ },
  29  {   1529,   78, /*  0.31 */ },
  30  {   1793,   76, /*  0.30 */ },
  31  {   2076,   74, /*  0.29 */ },
  32  {   2378,   72, /*  0.28 */ },
  33  {   2699,   71, /*  0.28 */ },
  34  {   3039,   69, /*  0.27 */ },
  35  {   3399,   68, /*  0.27 */ },
  36  {   3778,   66, /*  0.26 */ },
  37  {   4177,   65, /*  0.26 */ },
  38  {   4596,   64, /*  0.25 */ },
  39  {   5036,   62, /*  0.25 */ },
  40  {   5497,   61, /*  0.24 */ },
  41  {   5979,   60, /*  0.24 */ },
  42  {   6483,   59, /*  0.23 */ },
  43  {   7009,   58, /*  0.23 */ },
  44  {   7558,   57, /*  0.22 */ },
  45  {   8130,   56, /*  0.22 */ },
  46  {   8726,   55, /*  0.22 */ },
  47  {   9346,   54, /*  0.21 */ },
  48  {   9991,   53, /*  0.21 */ },
  49  {  10661,   52, /*  0.21 */ },
  50  {  11358,   52, /*  0.20 */ },
  51  {  12082,   51, /*  0.20 */ },
  52  {  12834,   50, /*  0.20 */ },
  53  {  13614,   49, /*  0.19 */ },
  54  {  14424,   48, /*  0.19 */ },
  55  {  15265,   48, /*  0.19 */ },
  56  {  16137,   47, /*  0.19 */ },
  57  {  17042,   46, /*  0.18 */ },
  58  {  17981,   45, /*  0.18 */ },
  59  {  18955,   45, /*  0.18 */ },
  60  {  19965,   44, /*  0.17 */ },
  61  {  21013,   43, /*  0.17 */ },
  62  {  22101,   43, /*  0.17 */ },
  63  {  23230,   42, /*  0.17 */ },
  64  {  24402,   41, /*  0.16 */ },
  65  {  25618,   41, /*  0.16 */ },
  66  {  26881,   40, /*  0.16 */ },
  67  {  28193,   39, /*  0.16 */ },
  68  {  29557,   39, /*  0.15 */ },
  69  {  30975,   38, /*  0.15 */ },
  70  {  32450,   38, /*  0.15 */ },
  71  {  33986,   37, /*  0.15 */ },
  72  {  35586,   36, /*  0.14 */ },
  73  {  37253,   36, /*  0.14 */ },
  74  {  38992,   35, /*  0.14 */ },
  75  {  40808,   35, /*  0.14 */ },
  76  {  42707,   34, /*  0.13 */ },
  77  {  44694,   33, /*  0.13 */ },
  78  {  46776,   33, /*  0.13 */ },
  79  {  48961,   32, /*  0.13 */ },
  80  {  51258,   32, /*  0.13 */ },
  81  {  53677,   31, /*  0.12 */ },
  82  {  56230,   30, /*  0.12 */ },
  83  {  58932,   30, /*  0.12 */ },
  84  {  61799,   29, /*  0.12 */ },
  85  {  64851,   28, /*  0.11 */ },
  86  {  68113,   28, /*  0.11 */ },
  87  {  71617,   27, /*  0.11 */ },
  88  {  75401,   26, /*  0.10 */ },
  89  {  79517,   26, /*  0.10 */ },
  90  {  84035,   25, /*  0.10 */ },
  91  {  89053,   24, /*  0.10 */ },
  92 };
  93
  94 #define HSTCP_AIMD_MAX  ARRAY_SIZE(hstcp_aimd_vals)
  95
  96 struct hstcp {
  97         u32     ai;
  98 };
  99
 100 static int max_ssthresh = 100;
 101 module_param(max_ssthresh, int, 0644);
 102 MODULE_PARM_DESC(max_ssthresh, "limited slow start threshold (RFC3742)");
 103
 104 static void hstcp_init(struct sock *sk)
 105 {
 106         struct tcp_sock *tp = tcp_sk(sk);
 107         struct hstcp *ca = inet_csk_ca(sk);
 108
 109         ca->ai = 0;
 110
 111         /* Ensure the MD arithmetic works.  This is somewhat pedantic,
 112          * since I don't think we will see a cwnd this large. :) */
 113         tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
 114 }
 115
 116 static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt,
 117                              u32 in_flight, int data_acked)
 118 {
 119         struct tcp_sock *tp = tcp_sk(sk);
 120         struct hstcp *ca = inet_csk_ca(sk);
 121
 122         if (!tcp_is_cwnd_limited(sk, in_flight))
 123                 return;
 124
 125         if (tp->snd_cwnd <= tp->snd_ssthresh) {
 126                 /* RFC3742: limited slow start
 127                  * the window is increased by 1/K MSS for each arriving ACK,
 128                  * for K = int(cwnd/(0.5 max_ssthresh))
 129                  */
 130                 if (max_ssthresh > 0 && tp->snd_cwnd > max_ssthresh) {
 131                         u32 k = max(tp->snd_cwnd / (max_ssthresh >> 1), 1U);
 132                         if (++tp->snd_cwnd_cnt >= k) {
 133                                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 134                                         tp->snd_cwnd++;
 135                                 tp->snd_cwnd_cnt = 0;
 136                         }
 137                 } else {
 138                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 139                                 tp->snd_cwnd++;
 140                 }
 141         } else {
 142                 /* Update AIMD parameters.
 143                  *
 144                  * We want to guarantee that:
 145                  *     hstcp_aimd_vals[ca->ai-1].cwnd <
 146                  *     snd_cwnd <=
 147                  *     hstcp_aimd_vals[ca->ai].cwnd
 148                  */
 149                 if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
 150                         while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
 151                                ca->ai < HSTCP_AIMD_MAX - 1)
 152                                 ca->ai++;
 153                 } else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
 154                         while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
 155                                 ca->ai--;
 156                 }
 157
 158                 /* Do additive increase */
 159                 if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
 160                         /* cwnd = cwnd + a(w) / cwnd */
 161                         tp->snd_cwnd_cnt += ca->ai + 1;
 162                         if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 163                                 tp->snd_cwnd_cnt -= tp->snd_cwnd;
 164                                 tp->snd_cwnd++;
 165                         }
 166                 }
 167         }
 168 }
 169
 170 static u32 hstcp_ssthresh(struct sock *sk)
 171 {
 172         const struct tcp_sock *tp = tcp_sk(sk);
 173         const struct hstcp *ca = inet_csk_ca(sk);
 174
 175         /* Do multiplicative decrease */
 176         return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
 177 }
 178
 179
 180 static struct tcp_congestion_ops tcp_highspeed = {
 181         .init           = hstcp_init,
 182         .ssthresh       = hstcp_ssthresh,
 183         .cong_avoid     = hstcp_cong_avoid,
 184         .min_cwnd       = tcp_reno_min_cwnd,
 185
 186         .owner          = THIS_MODULE,
 187         .name           = "highspeed"
 188 };
 189
 190 static int __init hstcp_register(void)
 191 {
 192         BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
 193         return tcp_register_congestion_control(&tcp_highspeed);
 194 }
 195
 196 static void __exit hstcp_unregister(void)
 197 {
 198         tcp_unregister_congestion_control(&tcp_highspeed);
 199 }
 200
 201 module_init(hstcp_register);
 202 module_exit(hstcp_unregister);
 203
 204 MODULE_AUTHOR("John Heffner");
 205 MODULE_LICENSE("GPL");
 206 MODULE_DESCRIPTION("High Speed TCP");