kernel-ark/net/ipv4/tcp_cubic.c
Sangtae Ha 6b3d626321 [TCP]: TCP cubic v2.2
We have updated CUBIC to fix some issues with slow increase in large
BDP networks. We also improved its convergence speed. The fix is in
fact very simple -- the window increase limit of smax during the
window probing phase (i.e., convex growth phase) is removed. We found
that this does not affect TCP friendliness, but only improves its
scalability. We have run some tests in our lab and also over the
Internet path from NCSU to Japan. These results can be seen from the
following page:

http://netsrv.csc.ncsu.edu/wiki/index.php/Intra_protocol_fairness_testing_with_linux-2.6.23.9
http://netsrv.csc.ncsu.edu/wiki/index.php/RTT_fairness_testing_with_linux-2.6.23.9
http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_friendliness_testing_with_linux-2.6.23.9

Signed-off-by: Sangtae Ha <sha2@ncsu.edu>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2008-03-04 14:17:41 -08:00

376 lines
10 KiB
C

/*
* TCP CUBIC: Binary Increase Congestion control for TCP v2.2
* Home page:
* http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
* 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://netsrv.csc.ncsu.edu/export/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_HZ 10 /* BIC HZ 2^10 = 1024 */
static int fast_convergence __read_mostly = 1;
static int beta __read_mostly = 717; /* = 717/1024 (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(beta, int, 0644);
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, 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*/
}
/* 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)
{
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("2.2");