netdev - Re: [PATCH v2 net] tcp: fix TLP timer not set when CA

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Date:   Sun, 24 Jan 2021 13:26:01 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Pengcheng Yang <yangpc@...gsu.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] tcp: fix TLP timer not set when CA_STATE changes
 from DISORDER to OPEN

On Sun, Jan 24, 2021 at 12:11 AM Pengcheng Yang <yangpc@...gsu.com> wrote:
>
> Upon receiving a cumulative ACK that changes the congestion state from
> Disorder to Open, the TLP timer is not set. If the sender is app-limited,
> it can only wait for the RTO timer to expire and retransmit.
>
> The reason for this is that the TLP timer is set before the congestion
> state changes in tcp_ack(), so we delay the time point of calling
> tcp_set_xmit_timer() until after tcp_fastretrans_alert() returns and
> remove the FLAG_SET_XMIT_TIMER from ack_flag when the RACK reorder timer
> is set.
>
> This commit has two additional benefits:
> 1) Make sure to reset RTO according to RFC6298 when receiving ACK, to
> avoid spurious RTO caused by RTO timer early expires.
> 2) Reduce the xmit timer reschedule once per ACK when the RACK reorder
> timer is set.
>
> Link: https://lore.kernel.org/netdev/1611311242-6675-1-git-send-email-yangpc@wangsu.com
> Signed-off-by: Pengcheng Yang <yangpc@...gsu.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> ---
> v2:
>  - modify the commit message according to Yuchung's suggestion
>

Thanks, Pengcheng! This seems to be missing the Fixes tag, but I guess
the maintainers can add it:

Fixes: df92c8394e6e ("tcp: fix xmit timer to only be reset if data
ACKed/SACKed")

Acked-by: Neal Cardwell <ncardwell@...gle.com>

neal