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

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Message-ID: <CADVnQymXKqcjEyNjTpK_c+eWbryZ0RL+4Y46_6DrOCVO_j+g7A@mail.gmail.com>
Date:   Thu, 17 Aug 2017 10:56:17 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     Netdev <netdev@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] tcp: when rearming RTO, if RTO time is in past then
 fire RTO ASAP

On Wed, Aug 16, 2017 at 5:53 PM, Neal Cardwell <ncardwell@...gle.com> wrote:
> 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>
> ---

Forgot to mention:

Fixes: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)")

This is a -stable candidate.

thanks,
neal