net/ipv4/tcp_scalable.c

   1 /* Tom Kelly's Scalable TCP
   2  *
   3  * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/
   4  *
   5  * John Heffner <jheffner@sc.edu>
   6  */
   7
   8 #include <linux/module.h>
   9 #include <net/tcp.h>
  10
  11 /* These factors derived from the recommended values in the aer:
  12  * .01 and and 7/8. We use 50 instead of 100 to account for
  13  * delayed ack.
  14  */
  15 #define TCP_SCALABLE_AI_CNT     50U
  16 #define TCP_SCALABLE_MD_SCALE   3
  17
  18 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
  19 {
  20         struct tcp_sock *tp = tcp_sk(sk);
  21
  22         if (!tcp_is_cwnd_limited(sk, in_flight))
  23                 return;
  24
  25         if (tp->snd_cwnd <= tp->snd_ssthresh)
  26                 tcp_slow_start(tp);
  27         else {
  28                 tp->snd_cwnd_cnt++;
  29                 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
  30                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
  31                                 tp->snd_cwnd++;
  32                         tp->snd_cwnd_cnt = 0;
  33                 }
  34         }
  35 }
  36
  37 static u32 tcp_scalable_ssthresh(struct sock *sk)
  38 {
  39         const struct tcp_sock *tp = tcp_sk(sk);
  40         return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
  41 }
  42
  43
  44 static struct tcp_congestion_ops tcp_scalable = {
  45         .ssthresh       = tcp_scalable_ssthresh,
  46         .cong_avoid     = tcp_scalable_cong_avoid,
  47         .min_cwnd       = tcp_reno_min_cwnd,
  48
  49         .owner          = THIS_MODULE,
  50         .name           = "scalable",
  51 };
  52
  53 static int __init tcp_scalable_register(void)
  54 {
  55         return tcp_register_congestion_control(&tcp_scalable);
  56 }
  57
  58 static void __exit tcp_scalable_unregister(void)
  59 {
  60         tcp_unregister_congestion_control(&tcp_scalable);
  61 }
  62
  63 module_init(tcp_scalable_register);
  64 module_exit(tcp_scalable_unregister);
  65
  66 MODULE_AUTHOR("John Heffner");
  67 MODULE_LICENSE("GPL");
  68 MODULE_DESCRIPTION("Scalable TCP");