netdev - Re: [PATCH net-next 2/3] tcp: implement coalescing on backlog queue

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Message-ID: <CADVnQykiiFz5H3J_vrCXHQ_FQ+Fg3qCZKoynsc_fdY_PcTx8cg@mail.gmail.com>
Date:   Thu, 22 Nov 2018 13:01:36 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, jean-louis@...ond.be,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 2/3] tcp: implement coalescing on backlog queue

On Wed, Nov 21, 2018 at 12:52 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> In case GRO is not as efficient as it should be or disabled,
> we might have a user thread trapped in __release_sock() while
> softirq handler flood packets up to the point we have to drop.
>
> This patch balances work done from user thread and softirq,
> to give more chances to __release_sock() to complete its work.
>
> This also helps if we receive many ACK packets, since GRO
> does not aggregate them.

Would this coalesce duplicate incoming ACK packets? Is there a risk
that this would eliminate incoming dupacks needed for fast recovery in
non-SACK connections? Perhaps pure ACKs should only be coalesced if
the ACK field is different?

neal