[TCP] H-TCP: Better time accounting

Instead of estimating the time since the last congestion event, count
it directly.

Signed-off-by: Baruch Even <baruch@ev-en.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_htcp.c

@@ -27,13 +27,12 @@ struct htcp {
 	u16	alpha;		/* Fixed point arith, << 7 */
 	u8	beta;           /* Fixed point arith, << 7 */
 	u8	modeswitch;     /* Delay modeswitch until we had at least one congestion event */
-	u8	ccount;		/* Number of RTTs since last congestion event */
+	u32	last_cong;	/* Time since last congestion event end */
-	u8	undo_ccount;
+	u32	undo_last_cong;
 	u16	pkts_acked;
 	u32	packetcount;
 	u32	minRTT;
 	u32	maxRTT;
-	u32	snd_cwnd_cnt2;
 
 	u32	undo_maxRTT;
 	u32	undo_old_maxB;
@@ -46,21 +45,30 @@ struct htcp {
 	u32	lasttime;
 };
 
+static inline u32 htcp_cong_time(struct htcp *ca)
+{
+	return jiffies - ca->last_cong;
+}
+
+static inline u32 htcp_ccount(struct htcp *ca)
+{
+	return htcp_cong_time(ca)/ca->minRTT;
+}
+
 static inline void htcp_reset(struct htcp *ca)
 {
-	ca->undo_ccount = ca->ccount;
+	ca->undo_last_cong = ca->last_cong;
 	ca->undo_maxRTT = ca->maxRTT;
 	ca->undo_old_maxB = ca->old_maxB;
 
-	ca->ccount = 0;
+	ca->last_cong = jiffies;
-	ca->snd_cwnd_cnt2 = 0;
 }
 
 static u32 htcp_cwnd_undo(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct htcp *ca = inet_csk_ca(sk);
-	ca->ccount = ca->undo_ccount;
+	ca->last_cong = ca->undo_last_cong;
 	ca->maxRTT = ca->undo_maxRTT;
 	ca->old_maxB = ca->undo_old_maxB;
 	return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
@@ -78,7 +86,7 @@ static inline void measure_rtt(struct sock *sk)
 		ca->minRTT = srtt;
 
 	/* max RTT */
-	if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) {
+	if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
 		if (ca->maxRTT < ca->minRTT)
 			ca->maxRTT = ca->minRTT;
 		if (ca->maxRTT < srtt && srtt <= ca->maxRTT+msecs_to_jiffies(20))
@@ -113,7 +121,7 @@ static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
 			&& now - ca->lasttime >= ca->minRTT
 			&& ca->minRTT > 0) {
 		__u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
-		if (ca->ccount <= 3) {
+		if (htcp_ccount(ca) <= 3) {
 			/* just after backoff */
 			ca->minB = ca->maxB = ca->Bi = cur_Bi;
 		} else {
@@ -158,7 +166,7 @@ static inline void htcp_alpha_update(struct htcp *ca)
 {
 	u32 minRTT = ca->minRTT;
 	u32 factor = 1;
-	u32 diff = ca->ccount * minRTT; /* time since last backoff */
+	u32 diff = htcp_cong_time(ca);
 
 	if (diff > HZ) {
 		diff -= HZ;
@@ -223,14 +231,6 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 
 		measure_rtt(sk);
 
-		/* keep track of number of round-trip times since last backoff event */
-		if (ca->snd_cwnd_cnt2 >= tp->snd_cwnd) {
-			ca->ccount++;
-			ca->snd_cwnd_cnt2 -= tp->snd_cwnd;
-			htcp_alpha_update(ca);
-		} else
-			ca->snd_cwnd_cnt2 += ca->pkts_acked;
-
 		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 		 */
@@ -238,6 +238,7 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 				tp->snd_cwnd++;
 			tp->snd_cwnd_cnt = 0;
+			htcp_alpha_update(ca);
 		} else
 			tp->snd_cwnd_cnt += ca->pkts_acked;
 
@@ -261,11 +262,18 @@ static void htcp_init(struct sock *sk)
 	ca->alpha = ALPHA_BASE;
 	ca->beta = BETA_MIN;
 	ca->pkts_acked = 1;
+	ca->last_cong = jiffies;
 }
 
 static void htcp_state(struct sock *sk, u8 new_state)
 {
 	switch (new_state) {
+	case TCP_CA_Open:
+		{
+			struct htcp *ca = inet_csk_ca(sk);
+			ca->last_cong = jiffies;
+		}
+		break;
 	case TCP_CA_CWR:
 	case TCP_CA_Recovery:
 	case TCP_CA_Loss: