net/ipv4/tcp_scalable.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Tom Kelly's Scalable TCP
   3  *
   4  * See http://www.deneholme.net/tom/scalable/
   5  *
   6  * John Heffner <jheffner@sc.edu>
   7  */
   8
   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 acked)
  20 {
  21         struct tcp_sock *tp = tcp_sk(sk);
  22
  23         if (!tcp_is_cwnd_limited(sk))
  24                 return;
  25
  26         if (tcp_in_slow_start(tp))
  27                 tcp_slow_start(tp, acked);
  28         else
  29                 tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
  30                                   1);
  31 }
  32
  33 static u32 tcp_scalable_ssthresh(struct sock *sk)
  34 {
  35         const struct tcp_sock *tp = tcp_sk(sk);
  36
  37         return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
  38 }
  39
  40 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
  41         .ssthresh       = tcp_scalable_ssthresh,
  42         .undo_cwnd      = tcp_reno_undo_cwnd,
  43         .cong_avoid     = tcp_scalable_cong_avoid,
  44
  45         .owner          = THIS_MODULE,
  46         .name           = "scalable",
  47 };
  48
  49 static int __init tcp_scalable_register(void)
  50 {
  51         return tcp_register_congestion_control(&tcp_scalable);
  52 }
  53
  54 static void __exit tcp_scalable_unregister(void)
  55 {
  56         tcp_unregister_congestion_control(&tcp_scalable);
  57 }
  58
  59 module_init(tcp_scalable_register);
  60 module_exit(tcp_scalable_unregister);
  61
  62 MODULE_AUTHOR("John Heffner");
  63 MODULE_LICENSE("GPL");
  64 MODULE_DESCRIPTION("Scalable TCP");