1 files changed, 159 insertions, 61 deletions

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 3aa0b23c1ea..a9bd8a4828a 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -1,12 +1,23 @@
 /*
- * TCP CUBIC: Binary Increase Congestion control for TCP v2.1
- *
+ * 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_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://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
+ *  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.
@@ -14,25 +25,35 @@
 
 #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_B		4	 /*
-					  * In binary search,
-					  * go to point (max+min)/N
-					  */
 #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	(4U<<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 max_increment __read_mostly = 16;
-static int beta __read_mostly = 819;	/* = 819/1024 (BICTCP_BETA_SCALE) */
+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 int hystart_ack_delta __read_mostly = 2;
+
 static u32 cube_rtt_scale __read_mostly;
 static u32 beta_scale __read_mostly;
 static u64 cube_factor __read_mostly;
@@ -40,9 +61,7 @@ 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_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");
@@ -50,6 +69,15 @@ 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");
+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");
+module_param(hystart_ack_delta, int, 0644);
+MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)");
 
 /* BIC TCP Parameters */
 struct bictcp {
@@ -60,19 +88,25 @@ struct bictcp {
 	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	delay_min;	/* min delay (msec << 3) */
 	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 */
+#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
+	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_ack;	/* 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->cnt = 0;
 	ca->last_max_cwnd = 0;
-	ca->loss_cwnd = 0;
 	ca->last_cwnd = 0;
 	ca->last_time = 0;
 	ca->bic_origin_point = 0;
@@ -82,12 +116,40 @@ 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 u32 bictcp_clock(void)
+{
+#if HZ < 1000
+	return ktime_to_ms(ktime_get_real());
+#else
+	return jiffies_to_msecs(jiffies);
+#endif
+}
+
+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_ack = bictcp_clock();
+	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)
+	struct bictcp *ca = inet_csk_ca(sk);
+
+	bictcp_reset(ca);
+	ca->loss_cwnd = 0;
+
+	if (hystart)
+		bictcp_hystart_reset(sk);
+
+	if (!hystart && initial_ssthresh)
 		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
 }
 
@@ -134,7 +196,7 @@ static u32 cubic_root(u64 a)
 	 * 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;
 }
@@ -144,8 +206,8 @@ static u32 cubic_root(u64 a)
  */
 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 {
-	u64 offs;
-	u32 delta, t, bic_target, min_cnt, max_cnt;
+	u32 delta, bic_target, max_cnt;
+	u64 offs, t;
 
 	ca->ack_cnt++;	/* count the number of ACKs */
 
@@ -188,9 +250,11 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 	 * if the cwnd < 1 million packets !!!
 	 */
 
+	t = (s32)(tcp_time_stamp - ca->epoch_start);
+	t += msecs_to_jiffies(ca->delay_min >> 3);
 	/* change the unit from HZ to bictcp_HZ */
-	t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
-	     << BICTCP_HZ) / HZ;
+	t <<= BICTCP_HZ;
+	do_div(t, HZ);
 
 	if (t < ca->bic_K)		/* t - K */
 		offs = ca->bic_K - t;
@@ -211,18 +275,12 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 		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;
+	/*
+	 * The initial growth of cubic function may be too conservative
+	 * when the available bandwidth is still unknown.
+	 */
+	if (ca->last_max_cwnd == 0 && ca->cnt > 20)
+		ca->cnt = 20;	/* increase cwnd 5% per RTT */
 
 	/* TCP Friendly */
 	if (tcp_friendliness) {
@@ -246,28 +304,21 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 		ca->cnt = 1;
 }
 
-static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
 
-	if (!tcp_is_cwnd_limited(sk, in_flight))
+	if (!tcp_is_cwnd_limited(sk))
 		return;
 
-	if (tp->snd_cwnd <= tp->snd_ssthresh)
-		tcp_slow_start(tp);
-	else {
+	if (tp->snd_cwnd <= tp->snd_ssthresh) {
+		if (hystart && after(ack, ca->end_seq))
+			bictcp_hystart_reset(sk);
+		tcp_slow_start(tp, acked);
+	} 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);
 	}
 
 }
@@ -295,13 +346,50 @@ 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);
+	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
 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 now = bictcp_clock();
+
+		/* first detection parameter - ack-train detection */
+		if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
+			ca->last_ack = now;
+			if ((s32)(now - 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
@@ -310,12 +398,17 @@ static void bictcp_state(struct sock *sk, u8 new_state)
 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;
 
 	if (icsk->icsk_ca_state == TCP_CA_Open) {
-		cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
-		ca->delayed_ack += cnt;
+		u32 ratio = ca->delayed_ack;
+
+		ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+		ratio += cnt;
+
+		ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT);
 	}
 
 	/* Some calls are for duplicates without timetamps */
@@ -323,19 +416,24 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
 		return;
 
 	/* Discard delay samples right after fast recovery */
-	if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
+	if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
 		return;
 
-	delay = usecs_to_jiffies(rtt_us) << 3;
+	delay = (rtt_us << 3) / USEC_PER_MSEC;
 	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;
+
+	/* 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 = {
+static struct tcp_congestion_ops cubictcp __read_mostly = {
 	.init		= bictcp_init,
 	.ssthresh	= bictcp_recalc_ssthresh,
 	.cong_avoid	= bictcp_cong_avoid,
@@ -391,4 +489,4 @@ module_exit(cubictcp_unregister);
 MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("CUBIC TCP");
-MODULE_VERSION("2.1");
+MODULE_VERSION("2.3");