// SPDX-License-Identifier: GPL-2.0-only

  /* Tom Kelly's Scalable TCP
   *

   * See http://www.deneholme.net/tom/scalable/

   *
   * John Heffner <jheffner@sc.edu>
   */

  #include <linux/module.h>
  #include <net/tcp.h>
  
  /* These factors derived from the recommended values in the aer:

   * .01 and 7/8.

   */

  #define TCP_SCALABLE_AI_CNT	100U

  #define TCP_SCALABLE_MD_SCALE	3

  static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)

  {

  	struct tcp_sock *tp = tcp_sk(sk);

  	if (!tcp_is_cwnd_limited(sk))

  		return;

  	if (tcp_in_slow_start(tp)) {
  		acked = tcp_slow_start(tp, acked);
  		if (!acked)
  			return;
  	}
  	tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
  			  acked);

  }

  static u32 tcp_scalable_ssthresh(struct sock *sk)

  {

  	const struct tcp_sock *tp = tcp_sk(sk);

  	return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
  }

  static struct tcp_congestion_ops tcp_scalable __read_mostly = {

  	.ssthresh	= tcp_scalable_ssthresh,

  	.undo_cwnd	= tcp_reno_undo_cwnd,

  	.cong_avoid	= tcp_scalable_cong_avoid,

  
  	.owner		= THIS_MODULE,
  	.name		= "scalable",
  };
  
  static int __init tcp_scalable_register(void)
  {
  	return tcp_register_congestion_control(&tcp_scalable);
  }
  
  static void __exit tcp_scalable_unregister(void)
  {
  	tcp_unregister_congestion_control(&tcp_scalable);
  }
  
  module_init(tcp_scalable_register);
  module_exit(tcp_scalable_unregister);
  
  MODULE_AUTHOR("John Heffner");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Scalable TCP");