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