1/*
2 * TCP Veno congestion control
3 *
4 * This is based on the congestion detection/avoidance scheme described in
5 *    C. P. Fu, S. C. Liew.
6 *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
7 *    IEEE Journal on Selected Areas in Communication,
8 *    Feb. 2003.
9 * 	See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
10 */
11
12#include <linux/mm.h>
13#include <linux/module.h>
14#include <linux/skbuff.h>
15#include <linux/inet_diag.h>
16
17#include <net/tcp.h>
18
19/* Default values of the Veno variables, in fixed-point representation
20 * with V_PARAM_SHIFT bits to the right of the binary point.
21 */
22#define V_PARAM_SHIFT 1
23static const int beta = 3 << V_PARAM_SHIFT;
24
25/* Veno variables */
26struct veno {
27	u8 doing_veno_now;	/* if true, do veno for this rtt */
28	u16 cntrtt;		/* # of rtts measured within last rtt */
29	u32 minrtt;		/* min of rtts measured within last rtt (in usec) */
30	u32 basertt;		/* the min of all Veno rtt measurements seen (in usec) */
31	u32 inc;		/* decide whether to increase cwnd */
32	u32 diff;		/* calculate the diff rate */
33};
34
35/* There are several situations when we must "re-start" Veno:
36 *
37 *  o when a connection is established
38 *  o after an RTO
39 *  o after fast recovery
40 *  o when we send a packet and there is no outstanding
41 *    unacknowledged data (restarting an idle connection)
42 *
43 */
44static inline void veno_enable(struct sock *sk)
45{
46	struct veno *veno = inet_csk_ca(sk);
47
48	/* turn on Veno */
49	veno->doing_veno_now = 1;
50
51	veno->minrtt = 0x7fffffff;
52}
53
54static inline void veno_disable(struct sock *sk)
55{
56	struct veno *veno = inet_csk_ca(sk);
57
58	/* turn off Veno */
59	veno->doing_veno_now = 0;
60}
61
62static void tcp_veno_init(struct sock *sk)
63{
64	struct veno *veno = inet_csk_ca(sk);
65
66	veno->basertt = 0x7fffffff;
67	veno->inc = 1;
68	veno_enable(sk);
69}
70
71/* Do rtt sampling needed for Veno. */
72static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
73{
74	struct veno *veno = inet_csk_ca(sk);
75	u32 vrtt;
76
77	if (rtt_us < 0)
78		return;
79
80	/* Never allow zero rtt or baseRTT */
81	vrtt = rtt_us + 1;
82
83	/* Filter to find propagation delay: */
84	if (vrtt < veno->basertt)
85		veno->basertt = vrtt;
86
87	/* Find the min rtt during the last rtt to find
88	 * the current prop. delay + queuing delay:
89	 */
90	veno->minrtt = min(veno->minrtt, vrtt);
91	veno->cntrtt++;
92}
93
94static void tcp_veno_state(struct sock *sk, u8 ca_state)
95{
96	if (ca_state == TCP_CA_Open)
97		veno_enable(sk);
98	else
99		veno_disable(sk);
100}
101
102/*
103 * If the connection is idle and we are restarting,
104 * then we don't want to do any Veno calculations
105 * until we get fresh rtt samples.  So when we
106 * restart, we reset our Veno state to a clean
107 * state. After we get acks for this flight of
108 * packets, _then_ we can make Veno calculations
109 * again.
110 */
111static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
112{
113	if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
114		tcp_veno_init(sk);
115}
116
117static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
118{
119	struct tcp_sock *tp = tcp_sk(sk);
120	struct veno *veno = inet_csk_ca(sk);
121
122	if (!veno->doing_veno_now) {
123		tcp_reno_cong_avoid(sk, ack, acked);
124		return;
125	}
126
127	/* limited by applications */
128	if (!tcp_is_cwnd_limited(sk))
129		return;
130
131	/* We do the Veno calculations only if we got enough rtt samples */
132	if (veno->cntrtt <= 2) {
133		/* We don't have enough rtt samples to do the Veno
134		 * calculation, so we'll behave like Reno.
135		 */
136		tcp_reno_cong_avoid(sk, ack, acked);
137	} else {
138		u64 target_cwnd;
139		u32 rtt;
140
141		/* We have enough rtt samples, so, using the Veno
142		 * algorithm, we determine the state of the network.
143		 */
144
145		rtt = veno->minrtt;
146
147		target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
148		target_cwnd <<= V_PARAM_SHIFT;
149		do_div(target_cwnd, rtt);
150
151		veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
152
153		if (tcp_in_slow_start(tp)) {
154			/* Slow start.  */
155			tcp_slow_start(tp, acked);
156		} else {
157			/* Congestion avoidance. */
158			if (veno->diff < beta) {
159				/* In the "non-congestive state", increase cwnd
160				 *  every rtt.
161				 */
162				tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
163			} else {
164				/* In the "congestive state", increase cwnd
165				 * every other rtt.
166				 */
167				if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
168					if (veno->inc &&
169					    tp->snd_cwnd < tp->snd_cwnd_clamp) {
170						tp->snd_cwnd++;
171						veno->inc = 0;
172					} else
173						veno->inc = 1;
174					tp->snd_cwnd_cnt = 0;
175				} else
176					tp->snd_cwnd_cnt++;
177			}
178		}
179		if (tp->snd_cwnd < 2)
180			tp->snd_cwnd = 2;
181		else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
182			tp->snd_cwnd = tp->snd_cwnd_clamp;
183	}
184	/* Wipe the slate clean for the next rtt. */
185	/* veno->cntrtt = 0; */
186	veno->minrtt = 0x7fffffff;
187}
188
189/* Veno MD phase */
190static u32 tcp_veno_ssthresh(struct sock *sk)
191{
192	const struct tcp_sock *tp = tcp_sk(sk);
193	struct veno *veno = inet_csk_ca(sk);
194
195	if (veno->diff < beta)
196		/* in "non-congestive state", cut cwnd by 1/5 */
197		return max(tp->snd_cwnd * 4 / 5, 2U);
198	else
199		/* in "congestive state", cut cwnd by 1/2 */
200		return max(tp->snd_cwnd >> 1U, 2U);
201}
202
203static struct tcp_congestion_ops tcp_veno __read_mostly = {
204	.init		= tcp_veno_init,
205	.ssthresh	= tcp_veno_ssthresh,
206	.cong_avoid	= tcp_veno_cong_avoid,
207	.pkts_acked	= tcp_veno_pkts_acked,
208	.set_state	= tcp_veno_state,
209	.cwnd_event	= tcp_veno_cwnd_event,
210
211	.owner		= THIS_MODULE,
212	.name		= "veno",
213};
214
215static int __init tcp_veno_register(void)
216{
217	BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
218	tcp_register_congestion_control(&tcp_veno);
219	return 0;
220}
221
222static void __exit tcp_veno_unregister(void)
223{
224	tcp_unregister_congestion_control(&tcp_veno);
225}
226
227module_init(tcp_veno_register);
228module_exit(tcp_veno_unregister);
229
230MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
231MODULE_LICENSE("GPL");
232MODULE_DESCRIPTION("TCP Veno");
233