2 * TCP Veno congestion control
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,
9 * See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
13 #include <linux/module.h>
14 #include <linux/skbuff.h>
15 #include <linux/inet_diag.h>
19 /* Default values of the Veno variables, in fixed-point representation
20 * with V_PARAM_SHIFT bits to the right of the binary point.
22 #define V_PARAM_SHIFT 1
23 static const int beta
= 3 << V_PARAM_SHIFT
;
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 */
35 /* There are several situations when we must "re-start" Veno:
37 * o when a connection is established
39 * o after fast recovery
40 * o when we send a packet and there is no outstanding
41 * unacknowledged data (restarting an idle connection)
44 static inline void veno_enable(struct sock
*sk
)
46 struct veno
*veno
= inet_csk_ca(sk
);
49 veno
->doing_veno_now
= 1;
51 veno
->minrtt
= 0x7fffffff;
54 static inline void veno_disable(struct sock
*sk
)
56 struct veno
*veno
= inet_csk_ca(sk
);
59 veno
->doing_veno_now
= 0;
62 static void tcp_veno_init(struct sock
*sk
)
64 struct veno
*veno
= inet_csk_ca(sk
);
66 veno
->basertt
= 0x7fffffff;
71 /* Do rtt sampling needed for Veno. */
72 static void tcp_veno_pkts_acked(struct sock
*sk
, u32 cnt
, s32 rtt_us
)
74 struct veno
*veno
= inet_csk_ca(sk
);
80 /* Never allow zero rtt or baseRTT */
83 /* Filter to find propagation delay: */
84 if (vrtt
< veno
->basertt
)
87 /* Find the min rtt during the last rtt to find
88 * the current prop. delay + queuing delay:
90 veno
->minrtt
= min(veno
->minrtt
, vrtt
);
94 static void tcp_veno_state(struct sock
*sk
, u8 ca_state
)
96 if (ca_state
== TCP_CA_Open
)
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
111 static void tcp_veno_cwnd_event(struct sock
*sk
, enum tcp_ca_event event
)
113 if (event
== CA_EVENT_CWND_RESTART
|| event
== CA_EVENT_TX_START
)
117 static void tcp_veno_cong_avoid(struct sock
*sk
, u32 ack
, u32 acked
,
120 struct tcp_sock
*tp
= tcp_sk(sk
);
121 struct veno
*veno
= inet_csk_ca(sk
);
123 if (!veno
->doing_veno_now
) {
124 tcp_reno_cong_avoid(sk
, ack
, acked
, in_flight
);
128 /* limited by applications */
129 if (!tcp_is_cwnd_limited(sk
, in_flight
))
132 /* We do the Veno calculations only if we got enough rtt samples */
133 if (veno
->cntrtt
<= 2) {
134 /* We don't have enough rtt samples to do the Veno
135 * calculation, so we'll behave like Reno.
137 tcp_reno_cong_avoid(sk
, ack
, acked
, in_flight
);
142 /* We have enough rtt samples, so, using the Veno
143 * algorithm, we determine the state of the network.
148 target_cwnd
= (tp
->snd_cwnd
* veno
->basertt
);
149 target_cwnd
<<= V_PARAM_SHIFT
;
150 do_div(target_cwnd
, rtt
);
152 veno
->diff
= (tp
->snd_cwnd
<< V_PARAM_SHIFT
) - target_cwnd
;
154 if (tp
->snd_cwnd
<= tp
->snd_ssthresh
) {
156 tcp_slow_start(tp
, acked
);
158 /* Congestion avoidance. */
159 if (veno
->diff
< beta
) {
160 /* In the "non-congestive state", increase cwnd
163 tcp_cong_avoid_ai(tp
, tp
->snd_cwnd
);
165 /* In the "congestive state", increase cwnd
168 if (tp
->snd_cwnd_cnt
>= tp
->snd_cwnd
) {
170 tp
->snd_cwnd
< tp
->snd_cwnd_clamp
) {
175 tp
->snd_cwnd_cnt
= 0;
181 if (tp
->snd_cwnd
< 2)
183 else if (tp
->snd_cwnd
> tp
->snd_cwnd_clamp
)
184 tp
->snd_cwnd
= tp
->snd_cwnd_clamp
;
186 /* Wipe the slate clean for the next rtt. */
187 /* veno->cntrtt = 0; */
188 veno
->minrtt
= 0x7fffffff;
192 static u32
tcp_veno_ssthresh(struct sock
*sk
)
194 const struct tcp_sock
*tp
= tcp_sk(sk
);
195 struct veno
*veno
= inet_csk_ca(sk
);
197 if (veno
->diff
< beta
)
198 /* in "non-congestive state", cut cwnd by 1/5 */
199 return max(tp
->snd_cwnd
* 4 / 5, 2U);
201 /* in "congestive state", cut cwnd by 1/2 */
202 return max(tp
->snd_cwnd
>> 1U, 2U);
205 static struct tcp_congestion_ops tcp_veno __read_mostly
= {
206 .flags
= TCP_CONG_RTT_STAMP
,
207 .init
= tcp_veno_init
,
208 .ssthresh
= tcp_veno_ssthresh
,
209 .cong_avoid
= tcp_veno_cong_avoid
,
210 .pkts_acked
= tcp_veno_pkts_acked
,
211 .set_state
= tcp_veno_state
,
212 .cwnd_event
= tcp_veno_cwnd_event
,
214 .owner
= THIS_MODULE
,
218 static int __init
tcp_veno_register(void)
220 BUILD_BUG_ON(sizeof(struct veno
) > ICSK_CA_PRIV_SIZE
);
221 tcp_register_congestion_control(&tcp_veno
);
225 static void __exit
tcp_veno_unregister(void)
227 tcp_unregister_congestion_control(&tcp_veno
);
230 module_init(tcp_veno_register
);
231 module_exit(tcp_veno_unregister
);
233 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
234 MODULE_LICENSE("GPL");
235 MODULE_DESCRIPTION("TCP Veno");