From cdbeb633ca71a02b7b63bfeb94994bf4e1a0b894 Mon Sep 17 00:00:00 2001 From: Neal Cardwell Date: Wed, 16 Aug 2017 17:53:36 -0400 Subject: [PATCH] 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: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)") Suggested-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- 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 53de142..bab7f04 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -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); -- 2.7.4