5528e568a7
Xiaoliang (David) Wei wrote:
> Hi gurus,
>
> I am reading the code of tcp_highspeed.c in the kernel and have a
> question on the hstcp_cong_avoid function, specifically the following
> AI part (line 136~143 in net/ipv4/tcp_highspeed.c ):
>
> /* Do additive increase */
> if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
> tp->snd_cwnd_cnt += ca->ai;
> if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
> tp->snd_cwnd++;
> tp->snd_cwnd_cnt -= tp->snd_cwnd;
> }
> }
>
> In this part, when (tp->snd_cwnd_cnt == tp->snd_cwnd),
> snd_cwnd_cnt will be -1... snd_cwnd_cnt is defined as u16, will this
> small chance of getting -1 becomes a problem?
> Shall we change it by reversing the order of the cwnd++ and cwnd_cnt -=
> cwnd?
Absolutely correct. Thanks.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
183 lines
4.8 KiB
C
183 lines
4.8 KiB
C
/*
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* Sally Floyd's High Speed TCP (RFC 3649) congestion control
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*
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* See http://www.icir.org/floyd/hstcp.html
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*
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* John Heffner <jheffner@psc.edu>
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*/
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#include <linux/config.h>
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#include <linux/module.h>
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#include <net/tcp.h>
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/* From AIMD tables from RFC 3649 appendix B,
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* with fixed-point MD scaled <<8.
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*/
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static const struct hstcp_aimd_val {
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unsigned int cwnd;
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unsigned int md;
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} hstcp_aimd_vals[] = {
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{ 38, 128, /* 0.50 */ },
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{ 118, 112, /* 0.44 */ },
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{ 221, 104, /* 0.41 */ },
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{ 347, 98, /* 0.38 */ },
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{ 495, 93, /* 0.37 */ },
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{ 663, 89, /* 0.35 */ },
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{ 851, 86, /* 0.34 */ },
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{ 1058, 83, /* 0.33 */ },
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{ 1284, 81, /* 0.32 */ },
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{ 1529, 78, /* 0.31 */ },
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{ 1793, 76, /* 0.30 */ },
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{ 2076, 74, /* 0.29 */ },
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{ 2378, 72, /* 0.28 */ },
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{ 2699, 71, /* 0.28 */ },
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{ 3039, 69, /* 0.27 */ },
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{ 3399, 68, /* 0.27 */ },
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{ 3778, 66, /* 0.26 */ },
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{ 4177, 65, /* 0.26 */ },
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{ 4596, 64, /* 0.25 */ },
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{ 5036, 62, /* 0.25 */ },
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{ 5497, 61, /* 0.24 */ },
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{ 5979, 60, /* 0.24 */ },
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{ 6483, 59, /* 0.23 */ },
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{ 7009, 58, /* 0.23 */ },
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{ 7558, 57, /* 0.22 */ },
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{ 8130, 56, /* 0.22 */ },
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{ 8726, 55, /* 0.22 */ },
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{ 9346, 54, /* 0.21 */ },
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{ 9991, 53, /* 0.21 */ },
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{ 10661, 52, /* 0.21 */ },
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{ 11358, 52, /* 0.20 */ },
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{ 12082, 51, /* 0.20 */ },
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{ 12834, 50, /* 0.20 */ },
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{ 13614, 49, /* 0.19 */ },
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{ 14424, 48, /* 0.19 */ },
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{ 15265, 48, /* 0.19 */ },
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{ 16137, 47, /* 0.19 */ },
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{ 17042, 46, /* 0.18 */ },
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{ 17981, 45, /* 0.18 */ },
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{ 18955, 45, /* 0.18 */ },
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{ 19965, 44, /* 0.17 */ },
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{ 21013, 43, /* 0.17 */ },
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{ 22101, 43, /* 0.17 */ },
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{ 23230, 42, /* 0.17 */ },
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{ 24402, 41, /* 0.16 */ },
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{ 25618, 41, /* 0.16 */ },
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{ 26881, 40, /* 0.16 */ },
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{ 28193, 39, /* 0.16 */ },
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{ 29557, 39, /* 0.15 */ },
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{ 30975, 38, /* 0.15 */ },
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{ 32450, 38, /* 0.15 */ },
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{ 33986, 37, /* 0.15 */ },
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{ 35586, 36, /* 0.14 */ },
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{ 37253, 36, /* 0.14 */ },
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{ 38992, 35, /* 0.14 */ },
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{ 40808, 35, /* 0.14 */ },
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{ 42707, 34, /* 0.13 */ },
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{ 44694, 33, /* 0.13 */ },
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{ 46776, 33, /* 0.13 */ },
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{ 48961, 32, /* 0.13 */ },
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{ 51258, 32, /* 0.13 */ },
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{ 53677, 31, /* 0.12 */ },
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{ 56230, 30, /* 0.12 */ },
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{ 58932, 30, /* 0.12 */ },
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{ 61799, 29, /* 0.12 */ },
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{ 64851, 28, /* 0.11 */ },
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{ 68113, 28, /* 0.11 */ },
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{ 71617, 27, /* 0.11 */ },
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{ 75401, 26, /* 0.10 */ },
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{ 79517, 26, /* 0.10 */ },
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{ 84035, 25, /* 0.10 */ },
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{ 89053, 24, /* 0.10 */ },
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};
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#define HSTCP_AIMD_MAX ARRAY_SIZE(hstcp_aimd_vals)
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struct hstcp {
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u32 ai;
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};
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static void hstcp_init(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct hstcp *ca = inet_csk_ca(sk);
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ca->ai = 0;
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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 hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt,
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u32 in_flight, int data_acked)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct hstcp *ca = inet_csk_ca(sk);
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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/* Update AIMD parameters */
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if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
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while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
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ca->ai < HSTCP_AIMD_MAX - 1)
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ca->ai++;
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} else if (tp->snd_cwnd < hstcp_aimd_vals[ca->ai].cwnd) {
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while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
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ca->ai > 0)
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ca->ai--;
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}
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/* Do additive increase */
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if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
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tp->snd_cwnd_cnt += ca->ai;
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if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
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tp->snd_cwnd_cnt -= tp->snd_cwnd;
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tp->snd_cwnd++;
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}
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}
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}
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}
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static u32 hstcp_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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const struct hstcp *ca = inet_csk_ca(sk);
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/* Do multiplicative decrease */
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return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
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}
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static struct tcp_congestion_ops tcp_highspeed = {
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.init = hstcp_init,
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.ssthresh = hstcp_ssthresh,
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.cong_avoid = hstcp_cong_avoid,
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.min_cwnd = tcp_reno_min_cwnd,
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.owner = THIS_MODULE,
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.name = "highspeed"
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};
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static int __init hstcp_register(void)
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{
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BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&tcp_highspeed);
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}
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static void __exit hstcp_unregister(void)
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{
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tcp_unregister_congestion_control(&tcp_highspeed);
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}
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module_init(hstcp_register);
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module_exit(hstcp_unregister);
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MODULE_AUTHOR("John Heffner");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("High Speed TCP");
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