// SPDX-License-Identifier: GPL-2.0-only
/*
* TCP Veno congestion control
*
* This is based on the congestion detection/avoidance scheme described in
* C. P. Fu, S. C. Liew.
* "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
* IEEE Journal on Selected Areas in Communication,
* Feb. 2003.
* See https://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>
#include <net/tcp.h>
/* Default values of the Veno variables, in fixed-point representation
* with V_PARAM_SHIFT bits to the right of the binary point.
*/
#define V_PARAM_SHIFT 1
static const int beta = 3 << V_PARAM_SHIFT;
/* Veno variables */
struct veno {
u8 doing_veno_now; /* if true, do veno for this rtt */
u16 cntrtt; /* # of rtts measured within last rtt */
u32 minrtt; /* min of rtts measured within last rtt (in usec) */
u32 basertt; /* the min of all Veno rtt measurements seen (in usec) */
u32 inc; /* decide whether to increase cwnd */
u32 diff; /* calculate the diff rate */
};
/* There are several situations when we must "re-start" Veno:
*
* o when a connection is established
* o after an RTO
* o after fast recovery
* o when we send a packet and there is no outstanding
* unacknowledged data (restarting an idle connection)
*
*/
static inline void veno_enable(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
/* turn on Veno */
veno->doing_veno_now = 1;
veno->minrtt = 0x7fffffff;
}
static inline void veno_disable(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
/* turn off Veno */
veno->doing_veno_now = 0;
}
static void tcp_veno_init(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
veno->basertt = 0x7fffffff;
veno->inc = 1;
veno_enable(sk);
}
/* Do rtt sampling needed for Veno. */
static void tcp_veno_pkts_acked(struct sock *sk,
const struct ack_sample *sample)
{
struct veno *veno = inet_csk_ca(sk);
u32 vrtt;
if (sample->rtt_us < 0)
return;
/* Never allow zero rtt or baseRTT */
vrtt = sample->rtt_us + 1;
/* Filter to find propagation delay: */
if (vrtt < veno->basertt)
veno->basertt = vrtt;
/* Find the min rtt during the last rtt to find
* the current prop. delay + queuing delay:
*/
veno->minrtt = min(veno->minrtt, vrtt);
veno->cntrtt++;
}
static void tcp_veno_state(struct sock *sk, u8 ca_state)
{
if (ca_state == TCP_CA_Open)
veno_enable(sk);
else
veno_disable(sk);
}
/*
* If the connection is idle and we are restarting,
* then we don't want to do any Veno calculations
* until we get fresh rtt samples. So when we
* restart, we reset our Veno state to a clean
* state. After we get acks for this flight of
* packets, _then_ we can make Veno calculations
* again.
*/
static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
tcp_veno_init(sk);
}
static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct veno *veno = inet_csk_ca(sk);
if (!veno->doing_veno_now) {
tcp_reno_cong_avoid(sk, ack, acked);
return;
}
/* limited by applications */
if (!tcp_is_cwnd_limited(sk))
return;
/* We do the Veno calculations only if we got enough rtt samples */
if (veno->cntrtt <= 2) {
/* We don't have enough rtt samples to do the Veno
* calculation, so we'll behave like Reno.
*/
tcp_reno_cong_avoid(sk, ack, acked);
} else {
u64 target_cwnd;
u32 rtt;
/* We have enough rtt samples, so, using the Veno
* algorithm, we determine the state of the network.
*/
rtt = veno->minrtt;
target_cwnd = (u64)tcp_snd_cwnd(tp) * veno->basertt;
target_cwnd <<= V_PARAM_SHIFT;
do_div(target_cwnd, rtt);
veno->diff = (tcp_snd_cwnd(tp) << V_PARAM_SHIFT) - target_cwnd;
if (tcp_in_slow_start(tp)) {
/* Slow start. */
acked = tcp_slow_start(tp, acked);
if (!acked)
goto done;
}
/* Congestion avoidance. */
if (veno->diff < beta) {
/* In the "non-congestive state", increase cwnd
* every rtt.
*/
tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
} else {
/* In the "congestive state", increase cwnd
* every other rtt.
*/
if (tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
if (veno->inc &&
tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp) {
tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
veno->inc = 0;
} else
veno->inc = 1;
tp->snd_cwnd_cnt = 0;
} else
tp->snd_cwnd_cnt += acked;
}
done:
if (tcp_snd_cwnd(tp) < 2)
tcp_snd_cwnd_set(tp, 2);
else if (tcp_snd_cwnd(tp) > tp->snd_cwnd_clamp)
tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
}
/* Wipe the slate clean for the next rtt. */
/* veno->cntrtt = 0; */
veno->minrtt = 0x7fffffff;
}
/* Veno MD phase */
static u32 tcp_veno_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct veno *veno = inet_csk_ca(sk);
if (veno->diff < beta)
/* in "non-congestive state", cut cwnd by 1/5 */
return max(tcp_snd_cwnd(tp) * 4 / 5, 2U);
else
/* in "congestive state", cut cwnd by 1/2 */
return max(tcp_snd_cwnd(tp) >> 1U, 2U);
}
static struct tcp_congestion_ops tcp_veno __read_mostly = {
.init = tcp_veno_init,
.ssthresh = tcp_veno_ssthresh,
.undo_cwnd = tcp_reno_undo_cwnd,
.cong_avoid = tcp_veno_cong_avoid,
.pkts_acked = tcp_veno_pkts_acked,
.set_state = tcp_veno_state,
.cwnd_event = tcp_veno_cwnd_event,
.owner = THIS_MODULE,
.name = "veno",
};
static int __init tcp_veno_register(void)
{
BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
tcp_register_congestion_control(&tcp_veno);
return 0;
}
static void __exit tcp_veno_unregister(void)
{
tcp_unregister_congestion_control(&tcp_veno);
}
module_init(tcp_veno_register);
module_exit(tcp_veno_unregister);
MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Veno");
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