net/ipv4/tcp_htcp.c

   1 /*
   2  * H-TCP congestion control. The algorithm is detailed in:
   3  * R.N.Shorten, D.J.Leith:
   4  *   "H-TCP: TCP for high-speed and long-distance networks"
   5  *   Proc. PFLDnet, Argonne, 2004.
   6  * http://www.hamilton.ie/net/htcp3.pdf
   7  */
   8
   9 #include <linux/config.h>
  10 #include <linux/mm.h>
  11 #include <linux/module.h>
  12 #include <net/tcp.h>
  13
  14 #define ALPHA_BASE      (1<<7)  /* 1.0 with shift << 7 */
  15 #define BETA_MIN        (1<<6)  /* 0.5 with shift << 7 */
  16 #define BETA_MAX        102     /* 0.8 with shift << 7 */
  17
  18 static int use_rtt_scaling = 1;
  19 module_param(use_rtt_scaling, int, 0644);
  20 MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
  21
  22 static int use_bandwidth_switch = 1;
  23 module_param(use_bandwidth_switch, int, 0644);
  24 MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
  25
  26 struct htcp {
  27         u16     alpha;          /* Fixed point arith, << 7 */
  28         u8      beta;           /* Fixed point arith, << 7 */
  29         u8      modeswitch;     /* Delay modeswitch until we had at least one congestion event */
  30         u8      ccount;         /* Number of RTTs since last congestion event */
  31         u8      undo_ccount;
  32         u16     packetcount;
  33         u32     minRTT;
  34         u32     maxRTT;
  35         u32     snd_cwnd_cnt2;
  36
  37         u32     undo_maxRTT;
  38         u32     undo_old_maxB;
  39
  40         /* Bandwidth estimation */
  41         u32     minB;
  42         u32     maxB;
  43         u32     old_maxB;
  44         u32     Bi;
  45         u32     lasttime;
  46 };
  47
  48 static inline void htcp_reset(struct htcp *ca)
  49 {
  50         ca->undo_ccount = ca->ccount;
  51         ca->undo_maxRTT = ca->maxRTT;
  52         ca->undo_old_maxB = ca->old_maxB;
  53
  54         ca->ccount = 0;
  55         ca->snd_cwnd_cnt2 = 0;
  56 }
  57
  58 static u32 htcp_cwnd_undo(struct sock *sk)
  59 {
  60         const struct tcp_sock *tp = tcp_sk(sk);
  61         struct htcp *ca = inet_csk_ca(sk);
  62         ca->ccount = ca->undo_ccount;
  63         ca->maxRTT = ca->undo_maxRTT;
  64         ca->old_maxB = ca->undo_old_maxB;
  65         return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
  66 }
  67
  68 static inline void measure_rtt(struct sock *sk)
  69 {
  70         const struct inet_connection_sock *icsk = inet_csk(sk);
  71         const struct tcp_sock *tp = tcp_sk(sk);
  72         struct htcp *ca = inet_csk_ca(sk);
  73         u32 srtt = tp->srtt>>3;
  74
  75         /* keep track of minimum RTT seen so far, minRTT is zero at first */
  76         if (ca->minRTT > srtt || !ca->minRTT)
  77                 ca->minRTT = srtt;
  78
  79         /* max RTT */
  80         if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) {
  81                 if (ca->maxRTT < ca->minRTT)
  82                         ca->maxRTT = ca->minRTT;
  83                 if (ca->maxRTT < srtt && srtt <= ca->maxRTT+HZ/50)
  84                         ca->maxRTT = srtt;
  85         }
  86 }
  87
  88 static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
  89 {
  90         const struct inet_connection_sock *icsk = inet_csk(sk);
  91         const struct tcp_sock *tp = tcp_sk(sk);
  92         struct htcp *ca = inet_csk_ca(sk);
  93         u32 now = tcp_time_stamp;
  94
  95         /* achieved throughput calculations */
  96         if (icsk->icsk_ca_state != TCP_CA_Open &&
  97             icsk->icsk_ca_state != TCP_CA_Disorder) {
  98                 ca->packetcount = 0;
  99                 ca->lasttime = now;
 100                 return;
 101         }
 102
 103         ca->packetcount += pkts_acked;
 104
 105         if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)
 106                         && now - ca->lasttime >= ca->minRTT
 107                         && ca->minRTT > 0) {
 108                 __u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
 109                 if (ca->ccount <= 3) {
 110                         /* just after backoff */
 111                         ca->minB = ca->maxB = ca->Bi = cur_Bi;
 112                 } else {
 113                         ca->Bi = (3*ca->Bi + cur_Bi)/4;
 114                         if (ca->Bi > ca->maxB)
 115                                 ca->maxB = ca->Bi;
 116                         if (ca->minB > ca->maxB)
 117                                 ca->minB = ca->maxB;
 118                 }
 119                 ca->packetcount = 0;
 120                 ca->lasttime = now;
 121         }
 122 }
 123
 124 static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
 125 {
 126         if (use_bandwidth_switch) {
 127                 u32 maxB = ca->maxB;
 128                 u32 old_maxB = ca->old_maxB;
 129                 ca->old_maxB = ca->maxB;
 130
 131                 if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) {
 132                         ca->beta = BETA_MIN;
 133                         ca->modeswitch = 0;
 134                         return;
 135                 }
 136         }
 137
 138         if (ca->modeswitch && minRTT > max(HZ/100, 1) && maxRTT) {
 139                 ca->beta = (minRTT<<7)/maxRTT;
 140                 if (ca->beta < BETA_MIN)
 141                         ca->beta = BETA_MIN;
 142                 else if (ca->beta > BETA_MAX)
 143                         ca->beta = BETA_MAX;
 144         } else {
 145                 ca->beta = BETA_MIN;
 146                 ca->modeswitch = 1;
 147         }
 148 }
 149
 150 static inline void htcp_alpha_update(struct htcp *ca)
 151 {
 152         u32 minRTT = ca->minRTT;
 153         u32 factor = 1;
 154         u32 diff = ca->ccount * minRTT; /* time since last backoff */
 155
 156         if (diff > HZ) {
 157                 diff -= HZ;
 158                 factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ;
 159         }
 160
 161         if (use_rtt_scaling && minRTT) {
 162                 u32 scale = (HZ<<3)/(10*minRTT);
 163                 scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */
 164                 factor = (factor<<3)/scale;
 165                 if (!factor)
 166                         factor = 1;
 167         }
 168
 169         ca->alpha = 2*factor*((1<<7)-ca->beta);
 170         if (!ca->alpha)
 171                 ca->alpha = ALPHA_BASE;
 172 }
 173
 174 /* After we have the rtt data to calculate beta, we'd still prefer to wait one
 175  * rtt before we adjust our beta to ensure we are working from a consistent
 176  * data.
 177  *
 178  * This function should be called when we hit a congestion event since only at
 179  * that point do we really have a real sense of maxRTT (the queues en route
 180  * were getting just too full now).
 181  */
 182 static void htcp_param_update(struct sock *sk)
 183 {
 184         struct htcp *ca = inet_csk_ca(sk);
 185         u32 minRTT = ca->minRTT;
 186         u32 maxRTT = ca->maxRTT;
 187
 188         htcp_beta_update(ca, minRTT, maxRTT);
 189         htcp_alpha_update(ca);
 190
 191         /* add slowly fading memory for maxRTT to accommodate routing changes etc */
 192         if (minRTT > 0 && maxRTT > minRTT)
 193                 ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;
 194 }
 195
 196 static u32 htcp_recalc_ssthresh(struct sock *sk)
 197 {
 198         const struct tcp_sock *tp = tcp_sk(sk);
 199         const struct htcp *ca = inet_csk_ca(sk);
 200         htcp_param_update(sk);
 201         return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
 202 }
 203
 204 static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 205                             u32 in_flight, int data_acked)
 206 {
 207         struct tcp_sock *tp = tcp_sk(sk);
 208         struct htcp *ca = inet_csk_ca(sk);
 209
 210         if (in_flight < tp->snd_cwnd)
 211                 return;
 212
 213         if (tp->snd_cwnd <= tp->snd_ssthresh) {
 214                 /* In "safe" area, increase. */
 215                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 216                         tp->snd_cwnd++;
 217         } else {
 218                 measure_rtt(sk);
 219
 220                 /* keep track of number of round-trip times since last backoff event */
 221                 if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) {
 222                         ca->ccount++;
 223                         ca->snd_cwnd_cnt2 = 0;
 224                         htcp_alpha_update(ca);
 225                 }
 226
 227                 /* In dangerous area, increase slowly.
 228                  * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 229                  */
 230                 if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) {
 231                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 232                                 tp->snd_cwnd++;
 233                         tp->snd_cwnd_cnt = 0;
 234                         ca->ccount++;
 235                 }
 236         }
 237 }
 238
 239 /* Lower bound on congestion window. */
 240 static u32 htcp_min_cwnd(struct sock *sk)
 241 {
 242         const struct tcp_sock *tp = tcp_sk(sk);
 243         return tp->snd_ssthresh;
 244 }
 245
 246
 247 static void htcp_init(struct sock *sk)
 248 {
 249         struct htcp *ca = inet_csk_ca(sk);
 250
 251         memset(ca, 0, sizeof(struct htcp));
 252         ca->alpha = ALPHA_BASE;
 253         ca->beta = BETA_MIN;
 254 }
 255
 256 static void htcp_state(struct sock *sk, u8 new_state)
 257 {
 258         switch (new_state) {
 259         case TCP_CA_CWR:
 260         case TCP_CA_Recovery:
 261         case TCP_CA_Loss:
 262                 htcp_reset(inet_csk_ca(sk));
 263                 break;
 264         }
 265 }
 266
 267 static struct tcp_congestion_ops htcp = {
 268         .init           = htcp_init,
 269         .ssthresh       = htcp_recalc_ssthresh,
 270         .min_cwnd       = htcp_min_cwnd,
 271         .cong_avoid     = htcp_cong_avoid,
 272         .set_state      = htcp_state,
 273         .undo_cwnd      = htcp_cwnd_undo,
 274         .pkts_acked     = measure_achieved_throughput,
 275         .owner          = THIS_MODULE,
 276         .name           = "htcp",
 277 };
 278
 279 static int __init htcp_register(void)
 280 {
 281         BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
 282         BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
 283         if (!use_bandwidth_switch)
 284                 htcp.pkts_acked = NULL;
 285         return tcp_register_congestion_control(&htcp);
 286 }
 287
 288 static void __exit htcp_unregister(void)
 289 {
 290         tcp_unregister_congestion_control(&htcp);
 291 }
 292
 293 module_init(htcp_register);
 294 module_exit(htcp_unregister);
 295
 296 MODULE_AUTHOR("Baruch Even");
 297 MODULE_LICENSE("GPL");
 298 MODULE_DESCRIPTION("H-TCP");