Re: simplify microsecond rtt sampling

[John Heffner <jheffner@psc.edu>]

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Sigh.  Here's one that's not corrupted.  And for the record:


This changes the microsecond RTT sampling so that samples are taken in 
the same way that RTT samples are taken for the RTO calculator: on the 
last segment acknowledged, and only when the segment hasn't been 
retransmitted.


Signed-off-by: John Heffner <jheffner@psc.edu>

[-- Attachment #2: rtt_sample_fix.patch --]
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diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b5521a9..d0f6bd6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2228,13 +2228,12 @@ static int tcp_tso_acked(struct sock *sk
 	return acked;
 }
 
-static u32 tcp_usrtt(const struct sk_buff *skb)
+static u32 tcp_usrtt(struct timeval *tv)
 {
-	struct timeval tv, now;
+	struct timeval now;
 
 	do_gettimeofday(&now);
-	skb_get_timestamp(skb, &tv);
-	return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
+	return (now.tv_sec - tv->tv_sec) * 1000000 + (now.tv_usec - tv->tv_usec);
 }
 
 /* Remove acknowledged frames from the retransmission queue. */
@@ -2249,6 +2248,7 @@ static int tcp_clean_rtx_queue(struct so
 	u32 pkts_acked = 0;
 	void (*rtt_sample)(struct sock *sk, u32 usrtt)
 		= icsk->icsk_ca_ops->rtt_sample;
+	struct timeval tv;
 
 	while ((skb = skb_peek(&sk->sk_write_queue)) &&
 	       skb != sk->sk_send_head) {
@@ -2297,8 +2297,7 @@ static int tcp_clean_rtx_queue(struct so
 				seq_rtt = -1;
 			} else if (seq_rtt < 0) {
 				seq_rtt = now - scb->when;
-				if (rtt_sample)
-					(*rtt_sample)(sk, tcp_usrtt(skb));
+				skb_get_timestamp(skb, &tv);
 			}
 			if (sacked & TCPCB_SACKED_ACKED)
 				tp->sacked_out -= tcp_skb_pcount(skb);
@@ -2311,8 +2310,7 @@ static int tcp_clean_rtx_queue(struct so
 			}
 		} else if (seq_rtt < 0) {
 			seq_rtt = now - scb->when;
-			if (rtt_sample)
-				(*rtt_sample)(sk, tcp_usrtt(skb));
+			skb_get_timestamp(skb, &tv);
 		}
 		tcp_dec_pcount_approx(&tp->fackets_out, skb);
 		tcp_packets_out_dec(tp, skb);
@@ -2324,6 +2322,8 @@ static int tcp_clean_rtx_queue(struct so
 	if (acked&FLAG_ACKED) {
 		tcp_ack_update_rtt(sk, acked, seq_rtt);
 		tcp_ack_packets_out(sk, tp);
+		if (rtt_sample && !(acked & FLAG_RETRANS_DATA_ACKED))
+			(*rtt_sample)(sk, tcp_usrtt(&tv));
 
 		if (icsk->icsk_ca_ops->pkts_acked)
 			icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);