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 rtt,
  19                                     u32 in_flight, int flag)
  20 {
  21         struct tcp_sock *tp = tcp_sk(sk);
  22
  23         if (!tcp_is_cwnd_limited(sk, in_flight))
  24                 return;
  25
  26         if (tp->snd_cwnd <= tp->snd_ssthresh)
  27                 tcp_slow_start(tp);
  28         else {
  29                 tp->snd_cwnd_cnt++;
  30                 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
  31                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
  32                                 tp->snd_cwnd++;
  33                         tp->snd_cwnd_cnt = 0;
  34                 }
  35         }
  36 }
  37
  38 static u32 tcp_scalable_ssthresh(struct sock *sk)
  39 {
  40         const struct tcp_sock *tp = tcp_sk(sk);
  41         return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
  42 }
  43
  44
  45 static struct tcp_congestion_ops tcp_scalable = {
  46         .ssthresh       = tcp_scalable_ssthresh,
  47         .cong_avoid     = tcp_scalable_cong_avoid,
  48         .min_cwnd       = tcp_reno_min_cwnd,
  49
  50         .owner          = THIS_MODULE,
  51         .name           = "scalable",
  52 };
  53
  54 static int __init tcp_scalable_register(void)
  55 {
  56         return tcp_register_congestion_control(&tcp_scalable);
  57 }
  58
  59 static void __exit tcp_scalable_unregister(void)
  60 {
  61         tcp_unregister_congestion_control(&tcp_scalable);
  62 }
  63
  64 module_init(tcp_scalable_register);
  65 module_exit(tcp_scalable_unregister);
  66
  67 MODULE_AUTHOR("John Heffner");
  68 MODULE_LICENSE("GPL");
  69 MODULE_DESCRIPTION("Scalable TCP");