[TCP]: simplify microsecond rtt sampling

Simplify the code that comuputes microsecond rtt estimate used
by TCP Vegas. Move the callback out of the RTT sampler and into
the end of the ack cleanup.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -548,10 +548,9 @@ static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_
  * To save cycles in the RFC 1323 implementation it was better to break
  * it up into three procedures. -- erics
  */
-static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
+static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	const struct inet_connection_sock *icsk = inet_csk(sk);
 	long m = mrtt; /* RTT */
 
 	/*	The following amusing code comes from Jacobson's
@@ -610,9 +609,6 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
 		tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
 		tp->rtt_seq = tp->snd_nxt;
 	}
-
-	if (icsk->icsk_ca_ops->rtt_sample)
-		icsk->icsk_ca_ops->rtt_sample(sk, *usrtt);
 }
 
 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
@@ -1921,7 +1917,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 /* Read draft-ietf-tcplw-high-performance before mucking
  * with this code. (Superceeds RFC1323)
  */
-static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
+static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
 {
 	/* RTTM Rule: A TSecr value received in a segment is used to
 	 * update the averaged RTT measurement only if the segment
@@ -1940,13 +1936,13 @@ static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
 	 */
 	struct tcp_sock *tp = tcp_sk(sk);
 	const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
-	tcp_rtt_estimator(sk, seq_rtt, usrtt);
+	tcp_rtt_estimator(sk, seq_rtt);
 	tcp_set_rto(sk);
 	inet_csk(sk)->icsk_backoff = 0;
 	tcp_bound_rto(sk);
 }
 
-static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
+static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
 {
 	/* We don't have a timestamp. Can only use
 	 * packets that are not retransmitted to determine
@@ -1960,21 +1956,21 @@ static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag
 	if (flag & FLAG_RETRANS_DATA_ACKED)
 		return;
 
-	tcp_rtt_estimator(sk, seq_rtt, usrtt);
+	tcp_rtt_estimator(sk, seq_rtt);
 	tcp_set_rto(sk);
 	inet_csk(sk)->icsk_backoff = 0;
 	tcp_bound_rto(sk);
 }
 
 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
-				      const s32 seq_rtt, u32 *usrtt)
+				      const s32 seq_rtt)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
-		tcp_ack_saw_tstamp(sk, usrtt, flag);
+		tcp_ack_saw_tstamp(sk, flag);
 	else if (seq_rtt >= 0)
-		tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
+		tcp_ack_no_tstamp(sk, seq_rtt, flag);
 }
 
 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
@@ -2054,20 +2050,27 @@ static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
 	return acked;
 }
 
+static inline u32 tcp_usrtt(const struct sk_buff *skb)
+{
+	struct timeval tv, now;
+
+	do_gettimeofday(&now);
+	skb_get_timestamp(skb, &tv);
+	return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
+}
 
 /* Remove acknowledged frames from the retransmission queue. */
-static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
+static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct sk_buff *skb;
 	__u32 now = tcp_time_stamp;
 	int acked = 0;
 	__s32 seq_rtt = -1;
-	struct timeval usnow;
 	u32 pkts_acked = 0;
-
-	if (seq_usrtt)
-		do_gettimeofday(&usnow);
+	void (*rtt_sample)(struct sock *sk, u32 usrtt)
+		= icsk->icsk_ca_ops->rtt_sample;
 
 	while ((skb = skb_peek(&sk->sk_write_queue)) &&
 	       skb != sk->sk_send_head) {
@@ -2107,16 +2110,11 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt
 					tp->retrans_out -= tcp_skb_pcount(skb);
 				acked |= FLAG_RETRANS_DATA_ACKED;
 				seq_rtt = -1;
-			} else if (seq_rtt < 0)
+			} else if (seq_rtt < 0) {
 				seq_rtt = now - scb->when;
-			if (seq_usrtt) {
-				struct timeval tv;
-			
-				skb_get_timestamp(skb, &tv);
-				*seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000
-					+ (usnow.tv_usec - tv.tv_usec);
+				if (rtt_sample)
+					(*rtt_sample)(sk, tcp_usrtt(skb));
 			}
-
 			if (sacked & TCPCB_SACKED_ACKED)
 				tp->sacked_out -= tcp_skb_pcount(skb);
 			if (sacked & TCPCB_LOST)
@@ -2126,8 +2124,11 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt
 				    !before(scb->end_seq, tp->snd_up))
 					tp->urg_mode = 0;
 			}
-		} else if (seq_rtt < 0)
+		} else if (seq_rtt < 0) {
 			seq_rtt = now - scb->when;
+			if (rtt_sample)
+				(*rtt_sample)(sk, tcp_usrtt(skb));
+		}
 		tcp_dec_pcount_approx(&tp->fackets_out, skb);
 		tcp_packets_out_dec(tp, skb);
 		__skb_unlink(skb, &sk->sk_write_queue);
@@ -2135,8 +2136,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt
 	}
 
 	if (acked&FLAG_ACKED) {
-		const struct inet_connection_sock *icsk = inet_csk(sk);
-		tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
+		tcp_ack_update_rtt(sk, acked, seq_rtt);
 		tcp_ack_packets_out(sk, tp);
 
 		if (icsk->icsk_ca_ops->pkts_acked)
@@ -2299,7 +2299,6 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
 	u32 prior_in_flight;
 	s32 seq_rtt;
-	s32 seq_usrtt = 0;
 	int prior_packets;
 
 	/* If the ack is newer than sent or older than previous acks
@@ -2352,8 +2351,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	prior_in_flight = tcp_packets_in_flight(tp);
 
 	/* See if we can take anything off of the retransmit queue. */
-	flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
-				    icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL);
+	flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
 
 	if (tp->frto_counter)
 		tcp_process_frto(sk, prior_snd_una);
@@ -4242,7 +4240,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 				 */
 				if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
 				    !tp->srtt)
-					tcp_ack_saw_tstamp(sk, NULL, 0);
+					tcp_ack_saw_tstamp(sk, 0);
 
 				if (tp->rx_opt.tstamp_ok)
 					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;