netdev - Re: [PATCH net] tcp: when rearming RTO, if RTO time is in past then fire RTO ASAP

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Date:   Fri, 18 Aug 2017 16:08:20 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ncardwell@...gle.com
Cc:     netdev@...r.kernel.org, ycheng@...gle.com, edumazet@...gle.com
Subject: Re: [PATCH net] tcp: when rearming RTO, if RTO time is in past
 then fire RTO ASAP

From: Neal Cardwell <ncardwell@...gle.com>
Date: Wed, 16 Aug 2017 17:53:36 -0400

> 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.
> 
> 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>

Applied with Fixes: tag added and queued up for -stable, thanks Neal.