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authorStephen Hemminger <shemminger@linux-foundation.org>2007-04-23 22:24:32 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2007-04-25 22:29:44 -0700
commit65d1b4a7e73fe0e1f5275ad7d2d3547981480886 (patch)
tree27f91ead5c78c22641ff44037dc6a1acf4b54cbf /net/ipv4
parent[WIRELESS] drivers/net/wireless/Kconfig: correct minor typo (diff)
downloadlinux-dev-65d1b4a7e73fe0e1f5275ad7d2d3547981480886.tar.xz
linux-dev-65d1b4a7e73fe0e1f5275ad7d2d3547981480886.zip
[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: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp_illinois.c298
1 files changed, 186 insertions, 112 deletions
diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index 91a2a34604cd..ae6298600886 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -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");