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// SPDX-License-Identifier: GPL-2.0-only
/*
*
* YeAH TCP
*
* For further details look at:
* https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
*
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>
#include <net/tcp.h>
#include "tcp_vegas.h"
#define TCP_YEAH_ALPHA 80 /* number of packets queued at the bottleneck */
#define TCP_YEAH_GAMMA 1 /* fraction of queue to be removed per rtt */
#define TCP_YEAH_DELTA 3 /* log minimum fraction of cwnd to be removed on loss */
#define TCP_YEAH_EPSILON 1 /* log maximum fraction to be removed on early decongestion */
#define TCP_YEAH_PHY 8 /* maximum delta from base */
#define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */
#define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */
#define TCP_SCALABLE_AI_CNT 100U
/* YeAH variables */
struct yeah {
struct vegas vegas; /* must be first */
/* YeAH */
u32 lastQ;
u32 doing_reno_now;
u32 reno_count;
u32 fast_count;
};
static void tcp_yeah_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct yeah *yeah = inet_csk_ca(sk);
tcp_vegas_init(sk);
yeah->doing_reno_now = 0;
yeah->lastQ = 0;
yeah->reno_count = 2;
/* Ensure the MD arithmetic works. This is somewhat pedantic,
* since I don't think we will see a cwnd this large. :) */
tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
}
static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct yeah *yeah = inet_csk_ca(sk);
if (!tcp_is_cwnd_limited(sk))
return;
if (tcp_in_slow_start(tp)) {
acked = tcp_slow_start(tp, acked);
if (!acked)
goto do_vegas;
}
if (!yeah->doing_reno_now) {
/* Scalable */
tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
acked);
} else {
/* Reno */
tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
}
/* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
*
* These are so named because they represent the approximate values
* of snd_una and snd_nxt at the beginning of the current RTT. More
* precisely, they represent the amount of data sent during the RTT.
* At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
* we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
* bytes of data have been ACKed during the course of the RTT, giving
* an "actual" rate of:
*
* (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
*
* Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
* because delayed ACKs can cover more than one segment, so they
* don't line up yeahly with the boundaries of RTTs.
*
* Another unfortunate fact of life is that delayed ACKs delay the
* advance of the left edge of our send window, so that the number
* of bytes we send in an RTT is often less than our cwnd will allow.
* So we keep track of our cwnd separately, in v_beg_snd_cwnd.
*/
do_vegas:
if (after(ack, yeah->vegas.beg_snd_nxt)) {
/* We do the Vegas calculations only if we got enough RTT
* samples that we can be reasonably sure that we got
* at least one RTT sample that wasn't from a delayed ACK.
* If we only had 2 samples total,
* then that means we're getting only 1 ACK per RTT, which
* means they're almost certainly delayed ACKs.
* If we have 3 samples, we should be OK.
*/
if (yeah->vegas.cntRTT > 2) {
u32 rtt, queue;
u64 bw;
/* We have enough RTT samples, so, using the Vegas
* algorithm, we determine if we should increase or
* decrease cwnd, and by how much.
*/
/* Pluck out the RTT we are using for the Vegas
* calculations. This is the min RTT seen during the
* last RTT. Taking the min filters out the effects
* of delayed ACKs, at the cost of noticing congestion
* a bit later.
*/
rtt = yeah->vegas.minRTT;
/* Compute excess number of packets above bandwidth
* Avoid doing full 64 bit divide.
*/
bw = tp->snd_cwnd;
bw *= rtt - yeah->vegas.baseRTT;
do_div(bw, rtt);
queue = bw;
if (queue > TCP_YEAH_ALPHA ||
rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
if (queue > TCP_YEAH_ALPHA &&
tp->snd_cwnd > yeah->reno_count) {
u32 reduction = min(queue / TCP_YEAH_GAMMA ,
tp->snd_cwnd >> TCP_YEAH_EPSILON);
tp->snd_cwnd -= reduction;
tp->snd_cwnd = max(tp->snd_cwnd,
yeah->reno_count);
tp->snd_ssthresh = tp->snd_cwnd;
}
if (yeah->reno_count <= 2)
yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
else
yeah->reno_count++;
yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
0xffffffU);
} else {
yeah->fast_count++;
if (yeah->fast_count > TCP_YEAH_ZETA) {
yeah->reno_count = 2;
yeah->fast_count = 0;
}
yeah->doing_reno_now = 0;
}
yeah->lastQ = queue;
}
/* Save the extent of the current window so we can use this
* at the end of the next RTT.
*/
yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt;
yeah->vegas.beg_snd_nxt = tp->snd_nxt;
yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
/* Wipe the slate clean for the next RTT. */
yeah->vegas.cntRTT = 0;
yeah->vegas.minRTT = 0x7fffffff;
}
}
static u32 tcp_yeah_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct yeah *yeah = inet_csk_ca(sk);
u32 reduction;
if (yeah->doing_reno_now < TCP_YEAH_RHO) {
reduction = yeah->lastQ;
reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
} else
reduction = max(tp->snd_cwnd>>1, 2U);
yeah->fast_count = 0;
yeah->reno_count = max(yeah->reno_count>>1, 2U);
return max_t(int, tp->snd_cwnd - reduction, 2);
}
static struct tcp_congestion_ops tcp_yeah __read_mostly = {
.init = tcp_yeah_init,
.ssthresh = tcp_yeah_ssthresh,
.undo_cwnd = tcp_reno_undo_cwnd,
.cong_avoid = tcp_yeah_cong_avoid,
.set_state = tcp_vegas_state,
.cwnd_event = tcp_vegas_cwnd_event,
.get_info = tcp_vegas_get_info,
.pkts_acked = tcp_vegas_pkts_acked,
.owner = THIS_MODULE,
.name = "yeah",
};
static int __init tcp_yeah_register(void)
{
BUILD_BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
tcp_register_congestion_control(&tcp_yeah);
return 0;
}
static void __exit tcp_yeah_unregister(void)
{
tcp_unregister_congestion_control(&tcp_yeah);
}
module_init(tcp_yeah_register);
module_exit(tcp_yeah_unregister);
MODULE_AUTHOR("Angelo P. Castellani");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("YeAH TCP");
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