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