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Date: Wed, 1 Nov 2017 22:26:24 +0100 From: Willy Tarreau <w@....eu> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, linux@...ck-us.net Cc: Neal Cardwell <ncardwell@...gle.com>, Yuchung Cheng <ycheng@...gle.com>, Eric Dumazet <edumazet@...gle.com>, "David S . Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu> Subject: [PATCH 3.10 083/139] tcp: when rearming RTO, if RTO time is in past then fire RTO ASAP From: Neal Cardwell <ncardwell@...gle.com> 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: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)") Suggested-by: Yuchung Cheng <ycheng@...gle.com> Signed-off-by: Neal Cardwell <ncardwell@...gle.com> Signed-off-by: Yuchung Cheng <ycheng@...gle.com> Signed-off-by: Eric Dumazet <edumazet@...gle.com> Signed-off-by: David S. Miller <davem@...emloft.net> [wt: no need for usec_to_jiffies conversion in 3.10] Signed-off-by: Willy Tarreau <w@....eu> --- net/ipv4/tcp_input.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 828835c..85dd09b 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2977,8 +2977,7 @@ 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); -- 2.8.0.rc2.1.gbe9624a
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