Commit febf0819 authored Mar 14, 2011 by stephen hemminger Committed by David S. Miller Mar 14, 2011

tcp: fix RTT for quick packets in congestion control



In the congestion control interface, the callback for each ACK
includes an estimated round trip time in microseconds.
Some algorithms need high resolution (Vegas style) but most only
need jiffie resolution.  If RTT is not accurate (like a retransmission)
-1 is used as a flag value.

When doing coarse resolution if RTT is less than a a jiffie
then 0 should be returned rather than no estimate. Otherwise algorithms
that expect good ack's to trigger slow start (like CUBIC Hystart)
will be confused.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a23c37f1

net/ipv4/tcp_input.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -3350,7 +3350,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
		net_invalid_timestamp()))
		rtt_us = ktime_us_delta(ktime_get_real(),
		last_ackt);
		else if (ca_seq_rtt > 0)
		else if (ca_seq_rtt >= 0)
		rtt_us = jiffies_to_usecs(ca_seq_rtt);
		}

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