netdev - Re: [PATCH net-next] tcp: ack immediately when a cwr packet arrives

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Message-ID: <36385AF4-4EE4-4237-84B8-1978B091E28B@fb.com>
Date:   Tue, 24 Jul 2018 17:42:46 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Alexei Starovoitov <ast@...com>,
        "Eric Dumazet" <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] tcp: ack immediately when a cwr packet arrives

Note that without this fix the 99% latencies when doing 10KB RPCs in a congested network using DCTCP are 40ms vs. 190us with the patch. Also note that these 40ms high tail latencies started after commit 3759824da87b30ce7a35b4873b62b0ba38905ef5 in Jul 2015, which triggered the bugs/features we are fixing/adding. I agree it is a debatable whether it is a bug fix or a feature improvement and I am fine either way.

Lawrence

On 7/24/18, 10:13 AM, "Neal Cardwell" <ncardwell@...gle.com> wrote:

    On Tue, Jul 24, 2018 at 1:07 PM Yuchung Cheng <ycheng@...gle.com> wrote:
    >
    > On Mon, Jul 23, 2018 at 7:23 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
    > > Should this go to net tree instead where all the other fixes went?
    > I am neutral but this feels more like a feature improvement

    I agree this feels like a feature improvement rather than a bug fix.

    neal