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

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commit cdbeb633ca71a02b7b63bfeb94994bf4e1a0b894 upstream.

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: 6ba8a3b19e ("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>
[wt: no need for usec_to_jiffies conversion in 3.10]

Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Neal Cardwell 2017-08-16 17:53:36 -04:00 committed by syphyr
parent 26ab90e01c
commit 71ac50dd96
1 changed files with 1 additions and 2 deletions
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3
net/ipv4/tcp_input.c
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@ -2978,8 +2978,7 @@ void tcp_rearm_rto(struct sock *sk)
/* delta may not be positive if the socket is locked
* when the retrans timer fires and is rescheduled.
*/
if (delta > 0)
rto = delta;
rto = max_t(int, delta, 1);
}
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
TCP_RTO_MAX);