/*
- * TCP CUBIC: Binary Increase Congestion control for TCP v2.2
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
* 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
+ * Sangtae Ha, Injong Rhee and Lisong Xu,
+ * "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
+ * in ACM SIGOPS Operating System Review, July 2008.
* Available from:
- * http://netsrv.csc.ncsu.edu/export/cubic-paper.pdf
+ * http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
+ *
+ * CUBIC integrates a new slow start algorithm, called HyStart.
+ * The details of HyStart are presented in
+ * Sangtae Ha and Injong Rhee,
+ * "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
+ * Available from:
+ * http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
+ *
+ * All testing results are available from:
+ * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
*
* 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 <linux/math64.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 */
+/* Two methods of hybrid slow start */
+#define HYSTART_ACK_TRAIN 0x1
+#define HYSTART_DELAY 0x2
+
+/* Number of delay samples for detecting the increase of delay */
+#define HYSTART_MIN_SAMPLES 8
+#define HYSTART_DELAY_MIN (2U<<3)
+#define HYSTART_DELAY_MAX (16U<<3)
+#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
+
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 int hystart __read_mostly = 1;
+static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
+static int hystart_low_window __read_mostly = 16;
+
static u32 cube_rtt_scale __read_mostly;
static u32 beta_scale __read_mostly;
static u64 cube_factor __read_mostly;
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");
+module_param(hystart, int, 0644);
+MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
+module_param(hystart_detect, int, 0644);
+MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
+ " 1: packet-train 2: delay 3: both packet-train and delay");
+module_param(hystart_low_window, int, 0644);
+MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
/* BIC TCP Parameters */
struct bictcp {
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 */
+ u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
+ u8 sample_cnt; /* number of samples to decide curr_rtt */
+ u8 found; /* the exit point is found? */
+ u32 round_start; /* beginning of each round */
+ u32 end_seq; /* end_seq of the round */
+ u32 last_jiffies; /* last time when the ACK spacing is close */
+ u32 curr_rtt; /* the minimum rtt of current round */
};
static inline void bictcp_reset(struct bictcp *ca)
ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
ca->ack_cnt = 0;
ca->tcp_cwnd = 0;
+ ca->found = 0;
+}
+
+static inline void bictcp_hystart_reset(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ ca->round_start = ca->last_jiffies = jiffies;
+ ca->end_seq = tp->snd_nxt;
+ ca->curr_rtt = 0;
+ ca->sample_cnt = 0;
}
static void bictcp_init(struct sock *sk)
{
bictcp_reset(inet_csk_ca(sk));
- if (initial_ssthresh)
+
+ if (hystart)
+ bictcp_hystart_reset(sk);
+
+ if (!hystart && initial_ssthresh)
tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
}
* x = ( 2 * x + a / x ) / 3
* k+1 k k
*/
- x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
+ x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
x = ((x * 341) >> 10);
return x;
}
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
- if (tp->snd_cwnd <= tp->snd_ssthresh)
+ if (tp->snd_cwnd <= tp->snd_ssthresh) {
+ if (hystart && after(ack, ca->end_seq))
+ bictcp_hystart_reset(sk);
tcp_slow_start(tp);
- else {
+ } 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++;
+ tcp_cong_avoid_ai(tp, ca->cnt);
}
}
static void bictcp_state(struct sock *sk, u8 new_state)
{
- if (new_state == TCP_CA_Loss)
+ if (new_state == TCP_CA_Loss) {
bictcp_reset(inet_csk_ca(sk));
+ bictcp_hystart_reset(sk);
+ }
+}
+
+static void hystart_update(struct sock *sk, u32 delay)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ if (!(ca->found & hystart_detect)) {
+ u32 curr_jiffies = jiffies;
+
+ /* first detection parameter - ack-train detection */
+ if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) {
+ ca->last_jiffies = curr_jiffies;
+ if (curr_jiffies - ca->round_start >= ca->delay_min>>4)
+ ca->found |= HYSTART_ACK_TRAIN;
+ }
+
+ /* obtain the minimum delay of more than sampling packets */
+ if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
+ if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
+ ca->curr_rtt = delay;
+
+ ca->sample_cnt++;
+ } else {
+ if (ca->curr_rtt > ca->delay_min +
+ HYSTART_DELAY_THRESH(ca->delay_min>>4))
+ ca->found |= HYSTART_DELAY;
+ }
+ /*
+ * Either one of two conditions are met,
+ * we exit from slow start immediately.
+ */
+ if (ca->found & hystart_detect)
+ tp->snd_ssthresh = tp->snd_cwnd;
+ }
}
/* Track delayed acknowledgment ratio using sliding window
static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
+ const struct tcp_sock *tp = tcp_sk(sk);
struct bictcp *ca = inet_csk_ca(sk);
u32 delay;
/* first time call or link delay decreases */
if (ca->delay_min == 0 || ca->delay_min > delay)
ca->delay_min = delay;
+
+ /* hystart triggers when cwnd is larger than some threshold */
+ if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&
+ tp->snd_cwnd >= hystart_low_window)
+ hystart_update(sk, delay);
}
static struct tcp_congestion_ops cubictcp = {
MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CUBIC TCP");
-MODULE_VERSION("2.2");
+MODULE_VERSION("2.3");
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff