[TCP]: add tcp_slow_start helper

Move all the code that does linear TCP slowstart to one
inline function to ease later patch to add ABC support.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -765,6 +765,16 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 			    (tp->snd_cwnd >> 2)));
 }
 
+/*
+ * Linear increase during slow start
+ */
+static inline void tcp_slow_start(struct tcp_sock *tp)
+{
+	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+		tp->snd_cwnd++;
+}
+
+
 static inline void tcp_sync_left_out(struct tcp_sock *tp)
 {
 	if (tp->rx_opt.sack_ok &&

net/ipv4/tcp_bic.c

@@ -220,14 +220,12 @@ static void bictcp_cong_avoid(struct sock *sk, u32 ack,
 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;
 
-	if (tp->snd_cwnd <= tp->snd_ssthresh) {
-		/* In "safe" area, increase. */
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
-	} else {
+	if (tp->snd_cwnd <= tp->snd_ssthresh)
+		tcp_slow_start(tp);
+	else {
 		bictcp_update(ca, tp->snd_cwnd);
 
-                /* In dangerous area, increase slowly.
+		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 		 */
 		if (tp->snd_cwnd_cnt >= ca->cnt) {

net/ipv4/tcp_cong.c

@@ -189,12 +189,11 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;
 
-        if (tp->snd_cwnd <= tp->snd_ssthresh) {
-                /* In "safe" area, increase. */
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
-	} else {
-                /* In dangerous area, increase slowly.
+	/* In "safe" area, increase. */
+        if (tp->snd_cwnd <= tp->snd_ssthresh)
+		tcp_slow_start(tp);
+	else {
+		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
 		 */
 		if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {

net/ipv4/tcp_highspeed.c

@@ -119,10 +119,9 @@ static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt,
 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;
 
-	if (tp->snd_cwnd <= tp->snd_ssthresh) {
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
-	} else {
+	if (tp->snd_cwnd <= tp->snd_ssthresh)
+		tcp_slow_start(tp);
+	else {
 		/* Update AIMD parameters */
 		if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
 			while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&

net/ipv4/tcp_htcp.c

@@ -210,11 +210,10 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;
 
-        if (tp->snd_cwnd <= tp->snd_ssthresh) {
-                /* In "safe" area, increase. */
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
-	} else {
+        if (tp->snd_cwnd <= tp->snd_ssthresh)
+		tcp_slow_start(tp);
+	else {
+
 		measure_rtt(sk);
 
 		/* keep track of number of round-trip times since last backoff event */
@@ -224,7 +223,7 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 			htcp_alpha_update(ca);
 		}
 
-                /* In dangerous area, increase slowly.
+		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 		 */
 		if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) {

net/ipv4/tcp_scalable.c

@@ -24,17 +24,16 @@ static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;
 
-	if (tp->snd_cwnd <= tp->snd_ssthresh) {
-		tp->snd_cwnd++;
-	} else {
+	if (tp->snd_cwnd <= tp->snd_ssthresh)
+		tcp_slow_start(tp);
+	else {
 		tp->snd_cwnd_cnt++;
 		if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
-			tp->snd_cwnd++;
+			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+				tp->snd_cwnd++;
 			tp->snd_cwnd_cnt = 0;
 		}
 	}
-	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
-	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
 static u32 tcp_scalable_ssthresh(struct sock *sk)

net/ipv4/tcp_vegas.c

@@ -236,8 +236,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
 			/* We don't have enough RTT samples to do the Vegas
 			 * calculation, so we'll behave like Reno.
 			 */
-			if (tp->snd_cwnd > tp->snd_ssthresh)
-				tp->snd_cwnd++;
+			tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, cnt);
 		} else {
 			u32 rtt, target_cwnd, diff;
 
@@ -275,7 +274,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
 			 */
 			diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
 
-			if (tp->snd_cwnd < tp->snd_ssthresh) {
+			if (tp->snd_cwnd <= tp->snd_ssthresh) {
 				/* Slow start.  */
 				if (diff > gamma) {
 					/* Going too fast. Time to slow down
@@ -295,6 +294,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
 							    V_PARAM_SHIFT)+1);
 
 				}
+				tcp_slow_start(tp);
 			} else {
 				/* Congestion avoidance. */
 				u32 next_snd_cwnd;
@@ -327,37 +327,17 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
 				else if (next_snd_cwnd < tp->snd_cwnd)
 					tp->snd_cwnd--;
 			}
-		}
 
-		/* Wipe the slate clean for the next RTT. */
-		vegas->cntRTT = 0;
-		vegas->minRTT = 0x7fffffff;
+			if (tp->snd_cwnd < 2)
+				tp->snd_cwnd = 2;
+			else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
+				tp->snd_cwnd = tp->snd_cwnd_clamp;
+		}
 	}
 
-	/* The following code is executed for every ack we receive,
-	 * except for conditions checked in should_advance_cwnd()
-	 * before the call to tcp_cong_avoid(). Mainly this means that
-	 * we only execute this code if the ack actually acked some
-	 * data.
-	 */
-
-	/* If we are in slow start, increase our cwnd in response to this ACK.
-	 * (If we are not in slow start then we are in congestion avoidance,
-	 * and adjust our congestion window only once per RTT. See the code
-	 * above.)
-	 */
-	if (tp->snd_cwnd <= tp->snd_ssthresh)
-		tp->snd_cwnd++;
-
-	/* to keep cwnd from growing without bound */
-	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
-
-	/* Make sure that we are never so timid as to reduce our cwnd below
-	 * 2 MSS.
-	 *
-	 * Going below 2 MSS would risk huge delayed ACKs from our receiver.
-	 */
-	tp->snd_cwnd = max(tp->snd_cwnd, 2U);
+	/* Wipe the slate clean for the next RTT. */
+	vegas->cntRTT = 0;
+	vegas->minRTT = 0x7fffffff;
 }
 
 /* Extract info for Tcp socket info provided via netlink. */