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 7/8.
  14  */
  15 #define TCP_SCALABLE_AI_CNT     100U
  16 #define TCP_SCALABLE_MD_SCALE   3
  17
  18 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)
  19 {
  20         struct tcp_sock *tp = tcp_sk(sk);
  21
  22         if (!tcp_is_cwnd_limited(sk))
  23                 return;
  24
  25         if (tcp_in_slow_start(tp)) {
  26                 acked = tcp_slow_start(tp, acked);
  27                 if (!acked)
  28                         return;
  29         }
  30         tcp_cong_avoid_ai(tp, min(tcp_snd_cwnd(tp), TCP_SCALABLE_AI_CNT),
  31                           acked);
  32 }
  33
  34 static u32 tcp_scalable_ssthresh(struct sock *sk)
  35 {
  36         const struct tcp_sock *tp = tcp_sk(sk);
  37
  38         return max(tcp_snd_cwnd(tp) - (tcp_snd_cwnd(tp)>>TCP_SCALABLE_MD_SCALE), 2U);
  39 }
  40
  41 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
  42         .ssthresh       = tcp_scalable_ssthresh,
  43         .undo_cwnd      = tcp_reno_undo_cwnd,
  44         .cong_avoid     = tcp_scalable_cong_avoid,
  45
  46         .owner          = THIS_MODULE,
  47         .name           = "scalable",
  48 };
  49
  50 static int __init tcp_scalable_register(void)
  51 {
  52         return tcp_register_congestion_control(&tcp_scalable);
  53 }
  54
  55 static void __exit tcp_scalable_unregister(void)
  56 {
  57         tcp_unregister_congestion_control(&tcp_scalable);
  58 }
  59
  60 module_init(tcp_scalable_register);
  61 module_exit(tcp_scalable_unregister);
  62
  63 MODULE_AUTHOR("John Heffner");
  64 MODULE_LICENSE("GPL");
  65 MODULE_DESCRIPTION("Scalable TCP");