2 * Binary Increase Congestion control for TCP
4 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
5 * This is from the implementation of BICTCP in
6 * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
7 * "Binary Increase Congestion Control for Fast, Long Distance
8 * Networks" in InfoComm 2004
10 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf
12 * Unless BIC is enabled and congestion window is large
13 * this behaves the same as the original Reno.
17 #include <linux/module.h>
21 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
22 * max_cwnd = snd_cwnd * beta
26 * go to point (max+min)/N
29 static int fast_convergence
= 1;
30 static int max_increment
= 16;
31 static int low_window
= 14;
32 static int beta
= 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
33 static int initial_ssthresh
;
34 static int smooth_part
= 20;
36 module_param(fast_convergence
, int, 0644);
37 MODULE_PARM_DESC(fast_convergence
, "turn on/off fast convergence");
38 module_param(max_increment
, int, 0644);
39 MODULE_PARM_DESC(max_increment
, "Limit on increment allowed during binary search");
40 module_param(low_window
, int, 0644);
41 MODULE_PARM_DESC(low_window
, "lower bound on congestion window (for TCP friendliness)");
42 module_param(beta
, int, 0644);
43 MODULE_PARM_DESC(beta
, "beta for multiplicative increase");
44 module_param(initial_ssthresh
, int, 0644);
45 MODULE_PARM_DESC(initial_ssthresh
, "initial value of slow start threshold");
46 module_param(smooth_part
, int, 0644);
47 MODULE_PARM_DESC(smooth_part
, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
50 /* BIC TCP Parameters */
52 u32 cnt
; /* increase cwnd by 1 after ACKs */
53 u32 last_max_cwnd
; /* last maximum snd_cwnd */
54 u32 loss_cwnd
; /* congestion window at last loss */
55 u32 last_cwnd
; /* the last snd_cwnd */
56 u32 last_time
; /* time when updated last_cwnd */
57 u32 epoch_start
; /* beginning of an epoch */
58 #define ACK_RATIO_SHIFT 4
59 u32 delayed_ack
; /* estimate the ratio of Packets/ACKs << 4 */
62 static inline void bictcp_reset(struct bictcp
*ca
)
65 ca
->last_max_cwnd
= 0;
70 ca
->delayed_ack
= 2 << ACK_RATIO_SHIFT
;
73 static void bictcp_init(struct sock
*sk
)
75 bictcp_reset(inet_csk_ca(sk
));
77 tcp_sk(sk
)->snd_ssthresh
= initial_ssthresh
;
81 * Compute congestion window to use.
83 static inline void bictcp_update(struct bictcp
*ca
, u32 cwnd
)
85 if (ca
->last_cwnd
== cwnd
&&
86 (s32
)(tcp_time_stamp
- ca
->last_time
) <= HZ
/ 32)
90 ca
->last_time
= tcp_time_stamp
;
92 if (ca
->epoch_start
== 0) /* record the beginning of an epoch */
93 ca
->epoch_start
= tcp_time_stamp
;
95 /* start off normal */
96 if (cwnd
<= low_window
) {
101 /* binary increase */
102 if (cwnd
< ca
->last_max_cwnd
) {
103 __u32 dist
= (ca
->last_max_cwnd
- cwnd
)
106 if (dist
> max_increment
)
107 /* linear increase */
108 ca
->cnt
= cwnd
/ max_increment
;
110 /* binary search increase */
111 ca
->cnt
= (cwnd
* smooth_part
) / BICTCP_B
;
113 /* binary search increase */
114 ca
->cnt
= cwnd
/ dist
;
116 /* slow start AMD linear increase */
117 if (cwnd
< ca
->last_max_cwnd
+ BICTCP_B
)
119 ca
->cnt
= (cwnd
* smooth_part
) / BICTCP_B
;
120 else if (cwnd
< ca
->last_max_cwnd
+ max_increment
*(BICTCP_B
-1))
122 ca
->cnt
= (cwnd
* (BICTCP_B
-1))
123 / (cwnd
- ca
->last_max_cwnd
);
125 /* linear increase */
126 ca
->cnt
= cwnd
/ max_increment
;
129 /* if in slow start or link utilization is very low */
130 if (ca
->loss_cwnd
== 0) {
131 if (ca
->cnt
> 20) /* increase cwnd 5% per RTT */
135 ca
->cnt
= (ca
->cnt
<< ACK_RATIO_SHIFT
) / ca
->delayed_ack
;
136 if (ca
->cnt
== 0) /* cannot be zero */
140 static void bictcp_cong_avoid(struct sock
*sk
, u32 ack
, u32 in_flight
)
142 struct tcp_sock
*tp
= tcp_sk(sk
);
143 struct bictcp
*ca
= inet_csk_ca(sk
);
145 if (!tcp_is_cwnd_limited(sk
, in_flight
))
148 if (tp
->snd_cwnd
<= tp
->snd_ssthresh
)
151 bictcp_update(ca
, tp
->snd_cwnd
);
153 /* In dangerous area, increase slowly.
154 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
156 if (tp
->snd_cwnd_cnt
>= ca
->cnt
) {
157 if (tp
->snd_cwnd
< tp
->snd_cwnd_clamp
)
159 tp
->snd_cwnd_cnt
= 0;
167 * behave like Reno until low_window is reached,
168 * then increase congestion window slowly
170 static u32
bictcp_recalc_ssthresh(struct sock
*sk
)
172 const struct tcp_sock
*tp
= tcp_sk(sk
);
173 struct bictcp
*ca
= inet_csk_ca(sk
);
175 ca
->epoch_start
= 0; /* end of epoch */
177 /* Wmax and fast convergence */
178 if (tp
->snd_cwnd
< ca
->last_max_cwnd
&& fast_convergence
)
179 ca
->last_max_cwnd
= (tp
->snd_cwnd
* (BICTCP_BETA_SCALE
+ beta
))
180 / (2 * BICTCP_BETA_SCALE
);
182 ca
->last_max_cwnd
= tp
->snd_cwnd
;
184 ca
->loss_cwnd
= tp
->snd_cwnd
;
187 if (tp
->snd_cwnd
<= low_window
)
188 return max(tp
->snd_cwnd
>> 1U, 2U);
190 return max((tp
->snd_cwnd
* beta
) / BICTCP_BETA_SCALE
, 2U);
193 static u32
bictcp_undo_cwnd(struct sock
*sk
)
195 const struct tcp_sock
*tp
= tcp_sk(sk
);
196 const struct bictcp
*ca
= inet_csk_ca(sk
);
197 return max(tp
->snd_cwnd
, ca
->last_max_cwnd
);
200 static void bictcp_state(struct sock
*sk
, u8 new_state
)
202 if (new_state
== TCP_CA_Loss
)
203 bictcp_reset(inet_csk_ca(sk
));
206 /* Track delayed acknowledgment ratio using sliding window
207 * ratio = (15*ratio + sample) / 16
209 static void bictcp_acked(struct sock
*sk
, u32 cnt
, s32 rtt
)
211 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
213 if (icsk
->icsk_ca_state
== TCP_CA_Open
) {
214 struct bictcp
*ca
= inet_csk_ca(sk
);
215 cnt
-= ca
->delayed_ack
>> ACK_RATIO_SHIFT
;
216 ca
->delayed_ack
+= cnt
;
221 static struct tcp_congestion_ops bictcp
= {
223 .ssthresh
= bictcp_recalc_ssthresh
,
224 .cong_avoid
= bictcp_cong_avoid
,
225 .set_state
= bictcp_state
,
226 .undo_cwnd
= bictcp_undo_cwnd
,
227 .pkts_acked
= bictcp_acked
,
228 .owner
= THIS_MODULE
,
232 static int __init
bictcp_register(void)
234 BUILD_BUG_ON(sizeof(struct bictcp
) > ICSK_CA_PRIV_SIZE
);
235 return tcp_register_congestion_control(&bictcp
);
238 static void __exit
bictcp_unregister(void)
240 tcp_unregister_congestion_control(&bictcp
);
243 module_init(bictcp_register
);
244 module_exit(bictcp_unregister
);
246 MODULE_AUTHOR("Stephen Hemminger");
247 MODULE_LICENSE("GPL");
248 MODULE_DESCRIPTION("BIC TCP");