Commit cdbeb633 authored Aug 16, 2017 by Neal Cardwell Committed by David S. Miller Aug 18, 2017

tcp: when rearming RTO, if RTO time is in past then fire RTO ASAP



In some situations tcp_send_loss_probe() can realize that it's unable
to send a loss probe (TLP), and falls back to calling tcp_rearm_rto()
to schedule an RTO timer. In such cases, sometimes tcp_rearm_rto()
realizes that the RTO was eligible to fire immediately or at some
point in the past (delta_us <= 0). Previously in such cases
tcp_rearm_rto() was scheduling such "overdue" RTOs to happen at now +
icsk_rto, which caused needless delays of hundreds of milliseconds
(and non-linear behavior that made reproducible testing
difficult). This commit changes the logic to schedule "overdue" RTOs
ASAP, rather than at now + icsk_rto.

Fixes: 6ba8a3b1 ("tcp: Tail loss probe (TLP)")
Suggested-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent bc3aae2b

net/ipv4/tcp_input.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -3009,8 +3009,7 @@ void tcp_rearm_rto(struct sock *sk)
		/* delta_us may not be positive if the socket is locked
		* when the retrans timer fires and is rescheduled.
		*/
		if (delta_us > 0)
		rto = usecs_to_jiffies(delta_us);
		rto = usecs_to_jiffies(max_t(int, delta_us, 1));
		}
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
		TCP_RTO_MAX);

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