Commit 65d1b4a7 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by David S. Miller
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[TCP]: TCP Illinois update.



This version more closely matches the paper, and fixes several
math errors. The biggest difference is that it updates alpha/beta
once per RTT
Signed-off-by: default avatarStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 42431592
......@@ -23,74 +23,106 @@
#define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */
#define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */
#define ALPHA_BASE ALPHA_SCALE /* 1.0 */
#define U32_MAX ((u32)~0U)
#define RTT_MAX (U32_MAX / ALPHA_MAX) /* 3.3 secs */
#define BETA_SHIFT 6
#define BETA_SCALE (1u<<BETA_SHIFT)
#define BETA_MIN (BETA_SCALE/8) /* 0.8 */
#define BETA_MAX (BETA_SCALE/2)
#define BETA_BASE BETA_MAX /* 0.5 */
#define THETA 5
#define BETA_MIN (BETA_SCALE/8) /* 0.125 */
#define BETA_MAX (BETA_SCALE/2) /* 0.5 */
#define BETA_BASE BETA_MAX
static int win_thresh __read_mostly = 15;
module_param(win_thresh, int, 0644);
module_param(win_thresh, int, 0);
MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
#define MAX_RTT 0x7fffffff
static int theta __read_mostly = 5;
module_param(theta, int, 0);
MODULE_PARM_DESC(theta, "# of fast RTT's before full growth");
/* TCP Illinois Parameters */
struct tcp_illinois {
u32 last_alpha;
u32 min_rtt;
u32 max_rtt;
u32 rtt_low;
u32 rtt_cnt;
u64 sum_rtt;
struct illinois {
u64 sum_rtt; /* sum of rtt's measured within last rtt */
u16 cnt_rtt; /* # of rtts measured within last rtt */
u32 base_rtt; /* min of all rtt in usec */
u32 max_rtt; /* max of all rtt in usec */
u32 end_seq; /* right edge of current RTT */
u32 alpha; /* Additive increase */
u32 beta; /* Muliplicative decrease */
u16 acked; /* # packets acked by current ACK */
u8 rtt_above; /* average rtt has gone above threshold */
u8 rtt_low; /* # of rtts measurements below threshold */
};
static void rtt_reset(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
ca->end_seq = tp->snd_nxt;
ca->cnt_rtt = 0;
ca->sum_rtt = 0;
/* TODO: age max_rtt? */
}
static void tcp_illinois_init(struct sock *sk)
{
struct tcp_illinois *ca = inet_csk_ca(sk);
struct illinois *ca = inet_csk_ca(sk);
ca->alpha = ALPHA_MAX;
ca->beta = BETA_BASE;
ca->base_rtt = 0x7fffffff;
ca->max_rtt = 0;
ca->acked = 0;
ca->rtt_low = 0;
ca->rtt_above = 0;
ca->last_alpha = ALPHA_BASE;
ca->min_rtt = 0x7fffffff;
rtt_reset(sk);
}
/*
* Keep track of min, max and average RTT
*/
static void tcp_illinois_rtt_calc(struct sock *sk, u32 rtt)
/* Measure RTT for each ack. */
static void tcp_illinois_rtt_sample(struct sock *sk, u32 rtt)
{
struct tcp_illinois *ca = inet_csk_ca(sk);
struct illinois *ca = inet_csk_ca(sk);
/* ignore bogus values, this prevents wraparound in alpha math */
if (rtt > RTT_MAX)
rtt = RTT_MAX;
if (rtt < ca->min_rtt)
ca->min_rtt = rtt;
if (rtt > ca->max_rtt)
/* keep track of minimum RTT seen so far */
if (ca->base_rtt > rtt)
ca->base_rtt = rtt;
/* and max */
if (ca->max_rtt < rtt)
ca->max_rtt = rtt;
if (++ca->rtt_cnt == 1)
ca->sum_rtt = rtt;
else
ca->sum_rtt += rtt;
++ca->cnt_rtt;
ca->sum_rtt += rtt;
}
/* max queuing delay */
static inline u32 max_delay(const struct tcp_illinois *ca)
/* Capture count of packets covered by ack, to adjust for delayed acks */
static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked)
{
return ca->max_rtt - ca->min_rtt;
struct illinois *ca = inet_csk_ca(sk);
ca->acked = pkts_acked;
}
/* average queueing delay */
static u32 avg_delay(struct tcp_illinois *ca)
/* Maximum queuing delay */
static inline u32 max_delay(const struct illinois *ca)
{
u64 avg_rtt = ca->sum_rtt;
do_div(avg_rtt, ca->rtt_cnt);
return ca->max_rtt - ca->base_rtt;
}
ca->sum_rtt = 0;
ca->rtt_cnt = 0;
/* Average queuing delay */
static inline u32 avg_delay(const struct illinois *ca)
{
u64 t = ca->sum_rtt;
return avg_rtt - ca->min_rtt;
do_div(t, ca->cnt_rtt);
return t - ca->base_rtt;
}
/*
......@@ -101,32 +133,31 @@ static u32 avg_delay(struct tcp_illinois *ca)
* A. If average delay is at minimum (we are uncongested),
* then use large alpha (10.0) to increase faster.
* B. If average delay is at maximum (getting congested)
* then use small alpha (1.0)
* then use small alpha (0.3)
*
* The result is a convex window growth curve.
*/
static u32 alpha(const struct sock *sk)
static u32 alpha(struct illinois *ca, u32 da, u32 dm)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_illinois *ca = inet_csk_ca(sk);
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
u32 d1, a;
u32 d1 = dm / 100; /* Low threshold */
if (tp->snd_cwnd < win_thresh)
return ALPHA_BASE; /* same as Reno (1.0) */
d1 = dm / 100;
if (da <= d1) {
/* Don't let noise force agressive response */
if (ca->rtt_low < THETA) {
++ca->rtt_low;
return ca->last_alpha;
} else
/* If never got out of low delay zone, then use max */
if (!ca->rtt_above)
return ALPHA_MAX;
/* Wait for 5 good RTT's before allowing alpha to go alpha max.
* This prevents one good RTT from causing sudden window increase.
*/
if (++ca->rtt_low < theta)
return ca->alpha;
ca->rtt_low = 0;
ca->rtt_above = 0;
return ALPHA_MAX;
}
ca->rtt_low = 0;
ca->rtt_above = 1;
/*
* Based on:
......@@ -146,37 +177,8 @@ static u32 alpha(const struct sock *sk)
dm -= d1;
da -= d1;
a = (dm * ALPHA_MAX) / (dm - (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
ca->last_alpha = a;
return a;
}
/*
* Increase window in response to successful acknowledgment.
*/
static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
u32 in_flight, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
/* RFC2861 only increase cwnd if fully utilized */
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
/* In slow start */
if (tp->snd_cwnd <= tp->snd_ssthresh)
tcp_slow_start(tp);
else {
/* additive increase cwnd += alpha / cwnd */
if ((tp->snd_cwnd_cnt * alpha(sk)) >> ALPHA_SHIFT >= tp->snd_cwnd) {
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
tp->snd_cwnd_cnt = 0;
} else
tp->snd_cwnd_cnt++;
}
return (dm * ALPHA_MAX) /
(dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
}
/*
......@@ -187,20 +189,14 @@ static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
* If delay is up to 80% of max then beta = 1/2
* In between is a linear function
*/
static inline u32 beta(struct sock *sk)
static u32 beta(u32 da, u32 dm)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_illinois *ca = inet_csk_ca(sk);
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
u32 d2, d3;
if (tp->snd_cwnd < win_thresh)
return BETA_BASE;
d2 = dm / 10;
if (da <= d2)
return BETA_MIN;
d3 = (8 * dm) / 10;
if (da >= d3 || d3 <= d2)
return BETA_MAX;
......@@ -222,31 +218,107 @@ static inline u32 beta(struct sock *sk)
/ (d3 - d2);
}
/* Update alpha and beta values once per RTT */
static void update_params(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
if (tp->snd_cwnd < win_thresh) {
ca->alpha = ALPHA_BASE;
ca->beta = BETA_BASE;
} else if (ca->cnt_rtt > 0) {
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
ca->alpha = alpha(ca, da, dm);
ca->beta = beta(da, dm);
}
rtt_reset(sk);
}
/*
* In case of loss, reset to default values
*/
static void tcp_illinois_state(struct sock *sk, u8 new_state)
{
struct illinois *ca = inet_csk_ca(sk);
if (new_state == TCP_CA_Loss) {
ca->alpha = ALPHA_BASE;
ca->beta = BETA_BASE;
ca->rtt_low = 0;
ca->rtt_above = 0;
rtt_reset(sk);
}
}
/*
* Increase window in response to successful acknowledgment.
*/
static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
u32 in_flight, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
if (after(ack, ca->end_seq))
update_params(sk);
/* RFC2861 only increase cwnd if fully utilized */
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
/* In slow start */
if (tp->snd_cwnd <= tp->snd_ssthresh)
tcp_slow_start(tp);
else {
u32 delta;
/* snd_cwnd_cnt is # of packets since last cwnd increment */
tp->snd_cwnd_cnt += ca->acked;
ca->acked = 1;
/* This is close approximation of:
* tp->snd_cwnd += alpha/tp->snd_cwnd
*/
delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
if (delta >= tp->snd_cwnd) {
tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
(u32) tp->snd_cwnd_clamp);
tp->snd_cwnd_cnt = 0;
}
}
}
static u32 tcp_illinois_ssthresh(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
/* Multiplicative decrease */
return max((tp->snd_cwnd * beta(sk)) >> BETA_SHIFT, 2U);
return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U);
}
/* Extract info for TCP socket info provided via netlink.
* We aren't really doing Vegas, but we can provide RTT info
*/
static void tcp_illinois_get_info(struct sock *sk, u32 ext,
struct sk_buff *skb)
/* Extract info for Tcp socket info provided via netlink. */
static void tcp_illinois_info(struct sock *sk, u32 ext,
struct sk_buff *skb)
{
const struct tcp_illinois *ca = inet_csk_ca(sk);
const struct illinois *ca = inet_csk_ca(sk);
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct tcpvegas_info info = {
.tcpv_enabled = 1,
.tcpv_rttcnt = ca->rtt_cnt,
.tcpv_minrtt = ca->min_rtt,
.tcpv_rttcnt = ca->cnt_rtt,
.tcpv_minrtt = ca->base_rtt,
};
u64 avg_rtt = ca->sum_rtt;
do_div(avg_rtt, ca->rtt_cnt);
info.tcpv_rtt = avg_rtt;
u64 t = ca->sum_rtt;
do_div(t, ca->cnt_rtt);
info.tcpv_rtt = t;
nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
}
......@@ -257,8 +329,10 @@ static struct tcp_congestion_ops tcp_illinois = {
.ssthresh = tcp_illinois_ssthresh,
.min_cwnd = tcp_reno_min_cwnd,
.cong_avoid = tcp_illinois_cong_avoid,
.rtt_sample = tcp_illinois_rtt_calc,
.get_info = tcp_illinois_get_info,
.set_state = tcp_illinois_state,
.rtt_sample = tcp_illinois_rtt_sample,
.get_info = tcp_illinois_info,
.pkts_acked = tcp_illinois_acked,
.owner = THIS_MODULE,
.name = "illinois",
......@@ -266,7 +340,7 @@ static struct tcp_congestion_ops tcp_illinois = {
static int __init tcp_illinois_register(void)
{
BUILD_BUG_ON(sizeof(struct tcp_illinois) > ICSK_CA_PRIV_SIZE);
BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcp_illinois);
}
......@@ -281,4 +355,4 @@ module_exit(tcp_illinois_unregister);
MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Illinois");
MODULE_VERSION("0.3");
MODULE_VERSION("1.0");
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