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[/] [test_project/] [trunk/] [linux_sd_driver/] [net/] [ipv4/] [tcp_cubic.c] - Blame information for rev 62

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/*
 * TCP CUBIC: Binary Increase Congestion control for TCP v2.1
 *
 * This is from the implementation of CUBIC TCP in
 * Injong Rhee, Lisong Xu.
 *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant
 *  in PFLDnet 2005
 * Available from:
 *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
 *
 * Unless CUBIC is enabled and congestion window is large
 * this behaves the same as the original Reno.
 */
 
#include <linux/mm.h>
#include <linux/module.h>
#include <net/tcp.h>
#include <asm/div64.h>
 
#define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
                                         * max_cwnd = snd_cwnd * beta
                                         */
#define BICTCP_B                4        /*
                                          * In binary search,
                                          * go to point (max+min)/N
                                          */
#define BICTCP_HZ               10      /* BIC HZ 2^10 = 1024 */
 
static int fast_convergence __read_mostly = 1;
static int max_increment __read_mostly = 16;
static int beta __read_mostly = 819;    /* = 819/1024 (BICTCP_BETA_SCALE) */
static int initial_ssthresh __read_mostly;
static int bic_scale __read_mostly = 41;
static int tcp_friendliness __read_mostly = 1;
 
static u32 cube_rtt_scale __read_mostly;
static u32 beta_scale __read_mostly;
static u64 cube_factor __read_mostly;
 
/* Note parameters that are used for precomputing scale factors are read-only */
module_param(fast_convergence, int, 0644);
MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
module_param(max_increment, int, 0644);
MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
module_param(beta, int, 0444);
MODULE_PARM_DESC(beta, "beta for multiplicative increase");
module_param(initial_ssthresh, int, 0644);
MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
module_param(bic_scale, int, 0444);
MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
module_param(tcp_friendliness, int, 0644);
MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
 
/* BIC TCP Parameters */
struct bictcp {
        u32     cnt;            /* increase cwnd by 1 after ACKs */
        u32     last_max_cwnd;  /* last maximum snd_cwnd */
        u32     loss_cwnd;      /* congestion window at last loss */
        u32     last_cwnd;      /* the last snd_cwnd */
        u32     last_time;      /* time when updated last_cwnd */
        u32     bic_origin_point;/* origin point of bic function */
        u32     bic_K;          /* time to origin point from the beginning of the current epoch */
        u32     delay_min;      /* min delay */
        u32     epoch_start;    /* beginning of an epoch */
        u32     ack_cnt;        /* number of acks */
        u32     tcp_cwnd;       /* estimated tcp cwnd */
#define ACK_RATIO_SHIFT 4
        u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
};
 
static inline void bictcp_reset(struct bictcp *ca)
{
        ca->cnt = 0;
        ca->last_max_cwnd = 0;
        ca->loss_cwnd = 0;
        ca->last_cwnd = 0;
        ca->last_time = 0;
        ca->bic_origin_point = 0;
        ca->bic_K = 0;
        ca->delay_min = 0;
        ca->epoch_start = 0;
        ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
        ca->ack_cnt = 0;
        ca->tcp_cwnd = 0;
}
 
static void bictcp_init(struct sock *sk)
{
        bictcp_reset(inet_csk_ca(sk));
        if (initial_ssthresh)
                tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
}
 
/* calculate the cubic root of x using a table lookup followed by one
 * Newton-Raphson iteration.
 * Avg err ~= 0.195%
 */
static u32 cubic_root(u64 a)
{
        u32 x, b, shift;
        /*
         * cbrt(x) MSB values for x MSB values in [0..63].
         * Precomputed then refined by hand - Willy Tarreau
         *
         * For x in [0..63],
         *   v = cbrt(x << 18) - 1
         *   cbrt(x) = (v[x] + 10) >> 6
         */
        static const u8 v[] = {
                /* 0x00 */    0,   54,   54,   54,  118,  118,  118,  118,
                /* 0x08 */  123,  129,  134,  138,  143,  147,  151,  156,
                /* 0x10 */  157,  161,  164,  168,  170,  173,  176,  179,
                /* 0x18 */  181,  185,  187,  190,  192,  194,  197,  199,
                /* 0x20 */  200,  202,  204,  206,  209,  211,  213,  215,
                /* 0x28 */  217,  219,  221,  222,  224,  225,  227,  229,
                /* 0x30 */  231,  232,  234,  236,  237,  239,  240,  242,
                /* 0x38 */  244,  245,  246,  248,  250,  251,  252,  254,
        };
 
        b = fls64(a);
        if (b < 7) {
                /* a in [0..63] */
                return ((u32)v[(u32)a] + 35) >> 6;
        }
 
        b = ((b * 84) >> 8) - 1;
        shift = (a >> (b * 3));
 
        x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
 
        /*
         * Newton-Raphson iteration
         *                         2
         * x    = ( 2 * x  +  a / x  ) / 3
         *  k+1          k         k
         */
        x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
        x = ((x * 341) >> 10);
        return x;
}
 
/*
 * Compute congestion window to use.
 */
static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
{
        u64 offs;
        u32 delta, t, bic_target, min_cnt, max_cnt;
 
        ca->ack_cnt++;  /* count the number of ACKs */
 
        if (ca->last_cwnd == cwnd &&
            (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
                return;
 
        ca->last_cwnd = cwnd;
        ca->last_time = tcp_time_stamp;
 
        if (ca->epoch_start == 0) {
                ca->epoch_start = tcp_time_stamp;       /* record the beginning of an epoch */
                ca->ack_cnt = 1;                        /* start counting */
                ca->tcp_cwnd = cwnd;                    /* syn with cubic */
 
                if (ca->last_max_cwnd <= cwnd) {
                        ca->bic_K = 0;
                        ca->bic_origin_point = cwnd;
                } else {
                        /* Compute new K based on
                         * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
                         */
                        ca->bic_K = cubic_root(cube_factor
                                               * (ca->last_max_cwnd - cwnd));
                        ca->bic_origin_point = ca->last_max_cwnd;
                }
        }
 
        /* cubic function - calc*/
        /* calculate c * time^3 / rtt,
         *  while considering overflow in calculation of time^3
         * (so time^3 is done by using 64 bit)
         * and without the support of division of 64bit numbers
         * (so all divisions are done by using 32 bit)
         *  also NOTE the unit of those veriables
         *        time  = (t - K) / 2^bictcp_HZ
         *        c = bic_scale >> 10
         * rtt  = (srtt >> 3) / HZ
         * !!! The following code does not have overflow problems,
         * if the cwnd < 1 million packets !!!
         */
 
        /* change the unit from HZ to bictcp_HZ */
        t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
             << BICTCP_HZ) / HZ;
 
        if (t < ca->bic_K)              /* t - K */
                offs = ca->bic_K - t;
        else
                offs = t - ca->bic_K;
 
        /* c/rtt * (t-K)^3 */
        delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
        if (t < ca->bic_K)                                      /* below origin*/
                bic_target = ca->bic_origin_point - delta;
        else                                                    /* above origin*/
                bic_target = ca->bic_origin_point + delta;
 
        /* cubic function - calc bictcp_cnt*/
        if (bic_target > cwnd) {
                ca->cnt = cwnd / (bic_target - cwnd);
        } else {
                ca->cnt = 100 * cwnd;              /* very small increment*/
        }
 
        if (ca->delay_min > 0) {
                /* max increment = Smax * rtt / 0.1  */
                min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
 
                /* use concave growth when the target is above the origin */
                if (ca->cnt < min_cnt && t >= ca->bic_K)
                        ca->cnt = min_cnt;
        }
 
        /* slow start and low utilization  */
        if (ca->loss_cwnd == 0)          /* could be aggressive in slow start */
                ca->cnt = 50;
 
        /* TCP Friendly */
        if (tcp_friendliness) {
                u32 scale = beta_scale;
                delta = (cwnd * scale) >> 3;
                while (ca->ack_cnt > delta) {           /* update tcp cwnd */
                        ca->ack_cnt -= delta;
                        ca->tcp_cwnd++;
                }
 
                if (ca->tcp_cwnd > cwnd){       /* if bic is slower than tcp */
                        delta = ca->tcp_cwnd - cwnd;
                        max_cnt = cwnd / delta;
                        if (ca->cnt > max_cnt)
                                ca->cnt = max_cnt;
                }
        }
 
        ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
        if (ca->cnt == 0)                        /* cannot be zero */
                ca->cnt = 1;
}
 
static void bictcp_cong_avoid(struct sock *sk, u32 ack,
                              u32 in_flight, int data_acked)
{
        struct tcp_sock *tp = tcp_sk(sk);
        struct bictcp *ca = inet_csk_ca(sk);
 
        if (!tcp_is_cwnd_limited(sk, in_flight))
                return;
 
        if (tp->snd_cwnd <= tp->snd_ssthresh)
                tcp_slow_start(tp);
        else {
                bictcp_update(ca, tp->snd_cwnd);
 
                /* In dangerous area, increase slowly.
                 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
                 */
                if (tp->snd_cwnd_cnt >= ca->cnt) {
                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                                tp->snd_cwnd++;
                        tp->snd_cwnd_cnt = 0;
                } else
                        tp->snd_cwnd_cnt++;
        }
 
}
 
static u32 bictcp_recalc_ssthresh(struct sock *sk)
{
        const struct tcp_sock *tp = tcp_sk(sk);
        struct bictcp *ca = inet_csk_ca(sk);
 
        ca->epoch_start = 0;     /* end of epoch */
 
        /* Wmax and fast convergence */
        if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
                ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
                        / (2 * BICTCP_BETA_SCALE);
        else
                ca->last_max_cwnd = tp->snd_cwnd;
 
        ca->loss_cwnd = tp->snd_cwnd;
 
        return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
}
 
static u32 bictcp_undo_cwnd(struct sock *sk)
{
        struct bictcp *ca = inet_csk_ca(sk);
 
        return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
}
 
static void bictcp_state(struct sock *sk, u8 new_state)
{
        if (new_state == TCP_CA_Loss)
                bictcp_reset(inet_csk_ca(sk));
}
 
/* Track delayed acknowledgment ratio using sliding window
 * ratio = (15*ratio + sample) / 16
 */
static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
{
        const struct inet_connection_sock *icsk = inet_csk(sk);
        struct bictcp *ca = inet_csk_ca(sk);
        u32 delay;
 
        if (icsk->icsk_ca_state == TCP_CA_Open) {
                cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
                ca->delayed_ack += cnt;
        }
 
        /* Some calls are for duplicates without timetamps */
        if (rtt_us < 0)
                return;
 
        /* Discard delay samples right after fast recovery */
        if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
                return;
 
        delay = usecs_to_jiffies(rtt_us) << 3;
        if (delay == 0)
                delay = 1;
 
        /* first time call or link delay decreases */
        if (ca->delay_min == 0 || ca->delay_min > delay)
                ca->delay_min = delay;
}
 
static struct tcp_congestion_ops cubictcp = {
        .init           = bictcp_init,
        .ssthresh       = bictcp_recalc_ssthresh,
        .cong_avoid     = bictcp_cong_avoid,
        .set_state      = bictcp_state,
        .undo_cwnd      = bictcp_undo_cwnd,
        .pkts_acked     = bictcp_acked,
        .owner          = THIS_MODULE,
        .name           = "cubic",
};
 
static int __init cubictcp_register(void)
{
        BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
 
        /* Precompute a bunch of the scaling factors that are used per-packet
         * based on SRTT of 100ms
         */
 
        beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
 
        cube_rtt_scale = (bic_scale * 10);      /* 1024*c/rtt */
 
        /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
         *  so K = cubic_root( (wmax-cwnd)*rtt/c )
         * the unit of K is bictcp_HZ=2^10, not HZ
         *
         *  c = bic_scale >> 10
         *  rtt = 100ms
         *
         * the following code has been designed and tested for
         * cwnd < 1 million packets
         * RTT < 100 seconds
         * HZ < 1,000,00  (corresponding to 10 nano-second)
         */
 
        /* 1/c * 2^2*bictcp_HZ * srtt */
        cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
 
        /* divide by bic_scale and by constant Srtt (100ms) */
        do_div(cube_factor, bic_scale * 10);
 
        return tcp_register_congestion_control(&cubictcp);
}
 
static void __exit cubictcp_unregister(void)
{
        tcp_unregister_congestion_control(&cubictcp);
}
 
module_init(cubictcp_register);
module_exit(cubictcp_unregister);
 
MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CUBIC TCP");
MODULE_VERSION("2.1");

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[/] [test_project/] [trunk/] [linux_sd_driver/] [net/] [ipv4/] [tcp_cubic.c] - Blame information for rev 62

Line No.	Rev	Author	Line
1	62	marcus.erl	`/*`
2			`* TCP CUBIC: Binary Increase Congestion control for TCP v2.1`
3			`*`
4			`* This is from the implementation of CUBIC TCP in`
5			`* Injong Rhee, Lisong Xu.`
6			`* "CUBIC: A New TCP-Friendly High-Speed TCP Variant`
7			`* in PFLDnet 2005`
8			`* Available from:`
9			`* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf`
10			`*`
11			`* Unless CUBIC is enabled and congestion window is large`
12			`* this behaves the same as the original Reno.`
13			`*/`
14
15			`#include <linux/mm.h>`
16			`#include <linux/module.h>`
17			`#include <net/tcp.h>`
18			`#include <asm/div64.h>`
19
20			`#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation`
21			`* max_cwnd = snd_cwnd * beta`
22			`*/`
23			`#define BICTCP_B 4 /*`
24			`* In binary search,`
25			`* go to point (max+min)/N`
26			`*/`
27			`#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */`
28
29			`static int fast_convergence __read_mostly = 1;`
30			`static int max_increment __read_mostly = 16;`
31			`static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */`
32			`static int initial_ssthresh __read_mostly;`
33			`static int bic_scale __read_mostly = 41;`
34			`static int tcp_friendliness __read_mostly = 1;`
35
36			`static u32 cube_rtt_scale __read_mostly;`
37			`static u32 beta_scale __read_mostly;`
38			`static u64 cube_factor __read_mostly;`
39
40			`/* Note parameters that are used for precomputing scale factors are read-only */`
41			`module_param(fast_convergence, int, 0644);`
42			`MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");`
43			`module_param(max_increment, int, 0644);`
44			`MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");`
45			`module_param(beta, int, 0444);`
46			`MODULE_PARM_DESC(beta, "beta for multiplicative increase");`
47			`module_param(initial_ssthresh, int, 0644);`
48			`MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");`
49			`module_param(bic_scale, int, 0444);`
50			`MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");`
51			`module_param(tcp_friendliness, int, 0644);`
52			`MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");`
53
54			`/* BIC TCP Parameters */`
55			`struct bictcp {`
56			`u32 cnt; /* increase cwnd by 1 after ACKs */`
57			`u32 last_max_cwnd; /* last maximum snd_cwnd */`
58			`u32 loss_cwnd; /* congestion window at last loss */`
59			`u32 last_cwnd; /* the last snd_cwnd */`
60			`u32 last_time; /* time when updated last_cwnd */`
61			`u32 bic_origin_point;/* origin point of bic function */`
62			`u32 bic_K; /* time to origin point from the beginning of the current epoch */`
63			`u32 delay_min; /* min delay */`
64			`u32 epoch_start; /* beginning of an epoch */`
65			`u32 ack_cnt; /* number of acks */`
66			`u32 tcp_cwnd; /* estimated tcp cwnd */`
67			`#define ACK_RATIO_SHIFT 4`
68			`u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */`
69			`};`
70
71			`static inline void bictcp_reset(struct bictcp *ca)`
72			`{`
73			`ca->cnt = 0;`
74			`ca->last_max_cwnd = 0;`
75			`ca->loss_cwnd = 0;`
76			`ca->last_cwnd = 0;`
77			`ca->last_time = 0;`
78			`ca->bic_origin_point = 0;`
79			`ca->bic_K = 0;`
80			`ca->delay_min = 0;`
81			`ca->epoch_start = 0;`
82			`ca->delayed_ack = 2 << ACK_RATIO_SHIFT;`
83			`ca->ack_cnt = 0;`
84			`ca->tcp_cwnd = 0;`
85			`}`
86
87			`static void bictcp_init(struct sock *sk)`
88			`{`
89			`bictcp_reset(inet_csk_ca(sk));`
90			`if (initial_ssthresh)`
91			`tcp_sk(sk)->snd_ssthresh = initial_ssthresh;`
92			`}`
93
94			`/* calculate the cubic root of x using a table lookup followed by one`
95			`* Newton-Raphson iteration.`
96			`* Avg err ~= 0.195%`
97			`*/`
98			`static u32 cubic_root(u64 a)`
99			`{`
100			`u32 x, b, shift;`
101			`/*`
102			`* cbrt(x) MSB values for x MSB values in [0..63].`
103			`* Precomputed then refined by hand - Willy Tarreau`
104			`*`
105			`* For x in [0..63],`
106			`* v = cbrt(x << 18) - 1`
107			`* cbrt(x) = (v[x] + 10) >> 6`
108			`*/`
109			`static const u8 v[] = {`
110			`/* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,`
111			`/* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,`
112			`/* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,`
113			`/* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,`
114			`/* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,`
115			`/* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,`
116			`/* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,`
117			`/* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,`
118			`};`
119
120			`b = fls64(a);`
121			`if (b < 7) {`
122			`/* a in [0..63] */`
123			`return ((u32)v[(u32)a] + 35) >> 6;`
124			`}`
125
126			`b = ((b * 84) >> 8) - 1;`
127			`shift = (a >> (b * 3));`
128
129			`x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;`
130
131			`/*`
132			`* Newton-Raphson iteration`
133			`* 2`
134			`* x = ( 2 * x + a / x ) / 3`
135			`* k+1 k k`
136			`*/`
137			`x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));`
138			`x = ((x * 341) >> 10);`
139			`return x;`
140			`}`
141
142			`/*`
143			`* Compute congestion window to use.`
144			`*/`
145			`static inline void bictcp_update(struct bictcp *ca, u32 cwnd)`
146			`{`
147			`u64 offs;`
148			`u32 delta, t, bic_target, min_cnt, max_cnt;`
149
150			`ca->ack_cnt++; /* count the number of ACKs */`
151
152			`if (ca->last_cwnd == cwnd &&`
153			`(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)`
154			`return;`
155
156			`ca->last_cwnd = cwnd;`
157			`ca->last_time = tcp_time_stamp;`
158
159			`if (ca->epoch_start == 0) {`
160			`ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */`
161			`ca->ack_cnt = 1; /* start counting */`
162			`ca->tcp_cwnd = cwnd; /* syn with cubic */`
163
164			`if (ca->last_max_cwnd <= cwnd) {`
165			`ca->bic_K = 0;`
166			`ca->bic_origin_point = cwnd;`
167			`} else {`
168			`/* Compute new K based on`
169			`* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)`
170			`*/`
171			`ca->bic_K = cubic_root(cube_factor`
172			`* (ca->last_max_cwnd - cwnd));`
173			`ca->bic_origin_point = ca->last_max_cwnd;`
174			`}`
175			`}`
176
177			`/* cubic function - calc*/`
178			`/* calculate c * time^3 / rtt,`
179			`* while considering overflow in calculation of time^3`
180			`* (so time^3 is done by using 64 bit)`
181			`* and without the support of division of 64bit numbers`
182			`* (so all divisions are done by using 32 bit)`
183			`* also NOTE the unit of those veriables`
184			`* time = (t - K) / 2^bictcp_HZ`
185			`* c = bic_scale >> 10`
186			`* rtt = (srtt >> 3) / HZ`
187			`* !!! The following code does not have overflow problems,`
188			`* if the cwnd < 1 million packets !!!`
189			`*/`
190
191			`/* change the unit from HZ to bictcp_HZ */`
192			`t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)`
193			`<< BICTCP_HZ) / HZ;`
194
195			`if (t < ca->bic_K) /* t - K */`
196			`offs = ca->bic_K - t;`
197			`else`
198			`offs = t - ca->bic_K;`
199
200			`/* c/rtt * (t-K)^3 */`
201			`delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);`
202			`if (t < ca->bic_K) /* below origin*/`
203			`bic_target = ca->bic_origin_point - delta;`
204			`else /* above origin*/`
205			`bic_target = ca->bic_origin_point + delta;`
206
207			`/* cubic function - calc bictcp_cnt*/`
208			`if (bic_target > cwnd) {`
209			`ca->cnt = cwnd / (bic_target - cwnd);`
210			`} else {`
211			`ca->cnt = 100 * cwnd; /* very small increment*/`
212			`}`
213
214			`if (ca->delay_min > 0) {`
215			`/* max increment = Smax * rtt / 0.1 */`
216			`min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);`
217
218			`/* use concave growth when the target is above the origin */`
219			`if (ca->cnt < min_cnt && t >= ca->bic_K)`
220			`ca->cnt = min_cnt;`
221			`}`
222
223			`/* slow start and low utilization */`
224			`if (ca->loss_cwnd == 0) /* could be aggressive in slow start */`
225			`ca->cnt = 50;`
226
227			`/* TCP Friendly */`
228			`if (tcp_friendliness) {`
229			`u32 scale = beta_scale;`
230			`delta = (cwnd * scale) >> 3;`
231			`while (ca->ack_cnt > delta) { /* update tcp cwnd */`
232			`ca->ack_cnt -= delta;`
233			`ca->tcp_cwnd++;`
234			`}`
235
236			`if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */`
237			`delta = ca->tcp_cwnd - cwnd;`
238			`max_cnt = cwnd / delta;`
239			`if (ca->cnt > max_cnt)`
240			`ca->cnt = max_cnt;`
241			`}`
242			`}`
243
244			`ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;`
245			`if (ca->cnt == 0) /* cannot be zero */`
246			`ca->cnt = 1;`
247			`}`
248
249			`static void bictcp_cong_avoid(struct sock *sk, u32 ack,`
250			`u32 in_flight, int data_acked)`
251			`{`
252			`struct tcp_sock *tp = tcp_sk(sk);`
253			`struct bictcp *ca = inet_csk_ca(sk);`
254
255			`if (!tcp_is_cwnd_limited(sk, in_flight))`
256			`return;`
257
258			`if (tp->snd_cwnd <= tp->snd_ssthresh)`
259			`tcp_slow_start(tp);`
260			`else {`
261			`bictcp_update(ca, tp->snd_cwnd);`
262
263			`/* In dangerous area, increase slowly.`
264			`* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd`
265			`*/`
266			`if (tp->snd_cwnd_cnt >= ca->cnt) {`
267			`if (tp->snd_cwnd < tp->snd_cwnd_clamp)`
268			`tp->snd_cwnd++;`
269			`tp->snd_cwnd_cnt = 0;`
270			`} else`
271			`tp->snd_cwnd_cnt++;`
272			`}`
273
274			`}`
275
276			`static u32 bictcp_recalc_ssthresh(struct sock *sk)`
277			`{`
278			`const struct tcp_sock *tp = tcp_sk(sk);`
279			`struct bictcp *ca = inet_csk_ca(sk);`
280
281			`ca->epoch_start = 0; /* end of epoch */`
282
283			`/* Wmax and fast convergence */`
284			`if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)`
285			`ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))`
286			`/ (2 * BICTCP_BETA_SCALE);`
287			`else`
288			`ca->last_max_cwnd = tp->snd_cwnd;`
289
290			`ca->loss_cwnd = tp->snd_cwnd;`
291
292			`return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);`
293			`}`
294
295			`static u32 bictcp_undo_cwnd(struct sock *sk)`
296			`{`
297			`struct bictcp *ca = inet_csk_ca(sk);`
298
299			`return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);`
300			`}`
301
302			`static void bictcp_state(struct sock *sk, u8 new_state)`
303			`{`
304			`if (new_state == TCP_CA_Loss)`
305			`bictcp_reset(inet_csk_ca(sk));`
306			`}`
307
308			`/* Track delayed acknowledgment ratio using sliding window`
309			`* ratio = (15*ratio + sample) / 16`
310			`*/`
311			`static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)`
312			`{`
313			`const struct inet_connection_sock *icsk = inet_csk(sk);`
314			`struct bictcp *ca = inet_csk_ca(sk);`
315			`u32 delay;`
316
317			`if (icsk->icsk_ca_state == TCP_CA_Open) {`
318			`cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;`
319			`ca->delayed_ack += cnt;`
320			`}`
321
322			`/* Some calls are for duplicates without timetamps */`
323			`if (rtt_us < 0)`
324			`return;`
325
326			`/* Discard delay samples right after fast recovery */`
327			`if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)`
328			`return;`
329
330			`delay = usecs_to_jiffies(rtt_us) << 3;`
331			`if (delay == 0)`
332			`delay = 1;`
333
334			`/* first time call or link delay decreases */`
335			`if (ca->delay_min == 0 \|\| ca->delay_min > delay)`
336			`ca->delay_min = delay;`
337			`}`
338
339			`static struct tcp_congestion_ops cubictcp = {`
340			`.init = bictcp_init,`
341			`.ssthresh = bictcp_recalc_ssthresh,`
342			`.cong_avoid = bictcp_cong_avoid,`
343			`.set_state = bictcp_state,`
344			`.undo_cwnd = bictcp_undo_cwnd,`
345			`.pkts_acked = bictcp_acked,`
346			`.owner = THIS_MODULE,`
347			`.name = "cubic",`
348			`};`
349
350			`static int __init cubictcp_register(void)`
351			`{`
352			`BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);`
353
354			`/* Precompute a bunch of the scaling factors that are used per-packet`
355			`* based on SRTT of 100ms`
356			`*/`
357
358			`beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);`
359
360			`cube_rtt_scale = (bic_scale * 10); /* 1024c/rtt /`
361
362			`/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3`
363			`* so K = cubic_root( (wmax-cwnd)*rtt/c )`
364			`* the unit of K is bictcp_HZ=2^10, not HZ`
365			`*`
366			`* c = bic_scale >> 10`
367			`* rtt = 100ms`
368			`*`
369			`* the following code has been designed and tested for`
370			`* cwnd < 1 million packets`
371			`* RTT < 100 seconds`
372			`* HZ < 1,000,00 (corresponding to 10 nano-second)`
373			`*/`
374
375			`/* 1/c * 2^2bictcp_HZ srtt */`
376			`cube_factor = 1ull << (10+3BICTCP_HZ); / 2^40 */`
377
378			`/* divide by bic_scale and by constant Srtt (100ms) */`
379			`do_div(cube_factor, bic_scale * 10);`
380
381			`return tcp_register_congestion_control(&cubictcp);`
382			`}`
383
384			`static void __exit cubictcp_unregister(void)`
385			`{`
386			`tcp_unregister_congestion_control(&cubictcp);`
387			`}`
388
389			`module_init(cubictcp_register);`
390			`module_exit(cubictcp_unregister);`
391
392			`MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");`
393			`MODULE_LICENSE("GPL");`
394			`MODULE_DESCRIPTION("CUBIC TCP");`
395			`MODULE_VERSION("2.1");`