1/*
2 *
3 *   YeAH TCP
4 *
5 * For further details look at:
6 *    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
7 *
8 */
9#include <linux/mm.h>
10#include <linux/module.h>
11#include <linux/skbuff.h>
12#include <linux/inet_diag.h>
13
14#include <net/tcp.h>
15
16#include "tcp_vegas.h"
17
18#define TCP_YEAH_ALPHA       80 //lin number of packets queued at the bottleneck
19#define TCP_YEAH_GAMMA        1 //lin fraction of queue to be removed per rtt
20#define TCP_YEAH_DELTA        3 //log minimum fraction of cwnd to be removed on loss
21#define TCP_YEAH_EPSILON      1 //log maximum fraction to be removed on early decongestion
22#define TCP_YEAH_PHY          8 //lin maximum delta from base
23#define TCP_YEAH_RHO         16 //lin minumum number of consecutive rtt to consider competition on loss
24#define TCP_YEAH_ZETA        50 //lin minimum number of state switchs to reset reno_count
25
26#define TCP_SCALABLE_AI_CNT	 100U
27
28/* YeAH variables */
29struct yeah {
30	struct vegas vegas;	/* must be first */
31
32	/* YeAH */
33	u32 lastQ;
34	u32 doing_reno_now;
35
36	u32 reno_count;
37	u32 fast_count;
38
39	u32 pkts_acked;
40};
41
42static void tcp_yeah_init(struct sock *sk)
43{
44	struct tcp_sock *tp = tcp_sk(sk);
45	struct yeah *yeah = inet_csk_ca(sk);
46
47	tcp_vegas_init(sk);
48
49	yeah->doing_reno_now = 0;
50	yeah->lastQ = 0;
51
52	yeah->reno_count = 2;
53
54	/* Ensure the MD arithmetic works.  This is somewhat pedantic,
55	 * since I don't think we will see a cwnd this large. :) */
56	tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
57
58}
59
60
61static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, ktime_t last)
62{
63	const struct inet_connection_sock *icsk = inet_csk(sk);
64	struct yeah *yeah = inet_csk_ca(sk);
65
66	if (icsk->icsk_ca_state == TCP_CA_Open)
67		yeah->pkts_acked = pkts_acked;
68
69	tcp_vegas_pkts_acked(sk, pkts_acked, last);
70}
71
72static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack,
73				u32 seq_rtt, u32 in_flight, int flag)
74{
75	struct tcp_sock *tp = tcp_sk(sk);
76	struct yeah *yeah = inet_csk_ca(sk);
77
78	if (!tcp_is_cwnd_limited(sk, in_flight))
79		return;
80
81	if (tp->snd_cwnd <= tp->snd_ssthresh)
82		tcp_slow_start(tp);
83
84	else if (!yeah->doing_reno_now) {
85		/* Scalable */
86
87		tp->snd_cwnd_cnt+=yeah->pkts_acked;
88		if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
89			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
90				tp->snd_cwnd++;
91			tp->snd_cwnd_cnt = 0;
92		}
93
94		yeah->pkts_acked = 1;
95
96	} else {
97		/* Reno */
98
99		if (tp->snd_cwnd_cnt < tp->snd_cwnd)
100			tp->snd_cwnd_cnt++;
101
102		if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
103			tp->snd_cwnd++;
104			tp->snd_cwnd_cnt = 0;
105		}
106	}
107
108	/* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
109	 *
110	 * These are so named because they represent the approximate values
111	 * of snd_una and snd_nxt at the beginning of the current RTT. More
112	 * precisely, they represent the amount of data sent during the RTT.
113	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
114	 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
115	 * bytes of data have been ACKed during the course of the RTT, giving
116	 * an "actual" rate of:
117	 *
118	 *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
119	 *
120	 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
121	 * because delayed ACKs can cover more than one segment, so they
122	 * don't line up yeahly with the boundaries of RTTs.
123	 *
124	 * Another unfortunate fact of life is that delayed ACKs delay the
125	 * advance of the left edge of our send window, so that the number
126	 * of bytes we send in an RTT is often less than our cwnd will allow.
127	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
128	 */
129
130	if (after(ack, yeah->vegas.beg_snd_nxt)) {
131
132		/* We do the Vegas calculations only if we got enough RTT
133		 * samples that we can be reasonably sure that we got
134		 * at least one RTT sample that wasn't from a delayed ACK.
135		 * If we only had 2 samples total,
136		 * then that means we're getting only 1 ACK per RTT, which
137		 * means they're almost certainly delayed ACKs.
138		 * If  we have 3 samples, we should be OK.
139		 */
140
141		if (yeah->vegas.cntRTT > 2) {
142			u32 rtt, queue;
143			u64 bw;
144
145			/* We have enough RTT samples, so, using the Vegas
146			 * algorithm, we determine if we should increase or
147			 * decrease cwnd, and by how much.
148			 */
149
150			/* Pluck out the RTT we are using for the Vegas
151			 * calculations. This is the min RTT seen during the
152			 * last RTT. Taking the min filters out the effects
153			 * of delayed ACKs, at the cost of noticing congestion
154			 * a bit later.
155			 */
156			rtt = yeah->vegas.minRTT;
157
158			/* Compute excess number of packets above bandwidth
159			 * Avoid doing full 64 bit divide.
160			 */
161			bw = tp->snd_cwnd;
162			bw *= rtt - yeah->vegas.baseRTT;
163			do_div(bw, rtt);
164			queue = bw;
165
166			if (queue > TCP_YEAH_ALPHA ||
167			    rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
168				if (queue > TCP_YEAH_ALPHA
169				    && tp->snd_cwnd > yeah->reno_count) {
170					u32 reduction = min(queue / TCP_YEAH_GAMMA ,
171							    tp->snd_cwnd >> TCP_YEAH_EPSILON);
172
173					tp->snd_cwnd -= reduction;
174
175					tp->snd_cwnd = max(tp->snd_cwnd,
176							   yeah->reno_count);
177
178					tp->snd_ssthresh = tp->snd_cwnd;
179				}
180
181				if (yeah->reno_count <= 2)
182					yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
183				else
184					yeah->reno_count++;
185
186				yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
187							   0xffffffU);
188			} else {
189				yeah->fast_count++;
190
191				if (yeah->fast_count > TCP_YEAH_ZETA) {
192					yeah->reno_count = 2;
193					yeah->fast_count = 0;
194				}
195
196				yeah->doing_reno_now = 0;
197			}
198
199			yeah->lastQ = queue;
200
201		}
202
203		/* Save the extent of the current window so we can use this
204		 * at the end of the next RTT.
205		 */
206		yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
207		yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
208		yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
209
210		/* Wipe the slate clean for the next RTT. */
211		yeah->vegas.cntRTT = 0;
212		yeah->vegas.minRTT = 0x7fffffff;
213	}
214}
215
216static u32 tcp_yeah_ssthresh(struct sock *sk) {
217	const struct tcp_sock *tp = tcp_sk(sk);
218	struct yeah *yeah = inet_csk_ca(sk);
219	u32 reduction;
220
221	if (yeah->doing_reno_now < TCP_YEAH_RHO) {
222		reduction = yeah->lastQ;
223
224		reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );
225
226		reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
227	} else
228		reduction = max(tp->snd_cwnd>>1,2U);
229
230	yeah->fast_count = 0;
231	yeah->reno_count = max(yeah->reno_count>>1, 2U);
232
233	return tp->snd_cwnd - reduction;
234}
235
236static struct tcp_congestion_ops tcp_yeah = {
237	.flags		= TCP_CONG_RTT_STAMP,
238	.init		= tcp_yeah_init,
239	.ssthresh	= tcp_yeah_ssthresh,
240	.cong_avoid	= tcp_yeah_cong_avoid,
241	.min_cwnd	= tcp_reno_min_cwnd,
242	.set_state	= tcp_vegas_state,
243	.cwnd_event	= tcp_vegas_cwnd_event,
244	.get_info	= tcp_vegas_get_info,
245	.pkts_acked	= tcp_yeah_pkts_acked,
246
247	.owner		= THIS_MODULE,
248	.name		= "yeah",
249};
250
251static int __init tcp_yeah_register(void)
252{
253	BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
254	tcp_register_congestion_control(&tcp_yeah);
255	return 0;
256}
257
258static void __exit tcp_yeah_unregister(void)
259{
260	tcp_unregister_congestion_control(&tcp_yeah);
261}
262
263module_init(tcp_yeah_register);
264module_exit(tcp_yeah_unregister);
265
266MODULE_AUTHOR("Angelo P. Castellani");
267MODULE_LICENSE("GPL");
268MODULE_DESCRIPTION("YeAH TCP");
269