netdev - Re: [PATCH net-next] tcp: optimise receiver buffer autotuning initialisation for high latency connections

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Message-ID: <170D5DF4-443F-47F6-B645-A8762E17A475@amazon.com>
Date:   Mon, 7 Dec 2020 17:16:43 +0000
From:   "Mohamed Abuelfotoh, Hazem" <abuehaze@...zon.com>
To:     Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "ycheng@...gle.com" <ycheng@...gle.com>,
        "weiwan@...gle.com" <weiwan@...gle.com>,
        "Strohman, Andy" <astroh@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>
Subject: Re: [PATCH net-next] tcp: optimise receiver buffer autotuning initialisation
 for high latency connections

    >Thanks for testing this, Eric. Would you be able to share the MTU
    >config commands you used, and the tcpdump traces you get? I'm
    >surprised that receive buffer autotuning would work for advmss of
    >around 6500 or higher.

Packet capture before applying the proposed patch

https://tcpautotuningpcaps.s3.eu-west-1.amazonaws.com/sender-bbr-bad-unpatched.pcap?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJNMP5ZZ3I4FAQGAQ%2F20201207%2Feu-west-1%2Fs3%2Faws4_request&X-Amz-Date=20201207T170123Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=a599a0e0e6632a957e5619007ba5ce4f63c8e8535ea24470b7093fef440a8300

Packet capture after applying the proposed patch

https://tcpautotuningpcaps.s3.eu-west-1.amazonaws.com/sender-bbr-good-patched.pcap?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJNMP5ZZ3I4FAQGAQ%2F20201207%2Feu-west-1%2Fs3%2Faws4_request&X-Amz-Date=20201207T165831Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=f18ec7246107590e8ac35c24322af699e4c2a73d174067c51cf6b0a06bbbca77

kernel version & MTU and configuration  from my receiver & sender is attached to this e-mail, please be aware that EC2 is doing MSS clamping so you need to configure MTU as 1500 on the sender side if you don’t have any MSS clamping between sender & receiver.

Thank you.

Hazem


On 07/12/2020, 16:34, "Neal Cardwell" <ncardwell@...gle.com> wrote:

    CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.



    On Mon, Dec 7, 2020 at 11:23 AM Eric Dumazet <edumazet@...gle.com> wrote:
    >
    > On Mon, Dec 7, 2020 at 5:09 PM Mohamed Abuelfotoh, Hazem
    > <abuehaze@...zon.com> wrote:
    > >
    > >     >Since I can not reproduce this problem with another NIC on x86, I
    > >     >really wonder if this is not an issue with ENA driver on PowerPC
    > >     >perhaps ?
    > >
    > >
    > > I am able to reproduce it on x86 based EC2 instances using ENA  or  Xen netfront or Intel ixgbevf driver on the receiver so it's not specific to ENA, we were able to easily reproduce it between 2 VMs running in virtual box on the same physical host considering the environment requirements I mentioned in my first e-mail.
    > >
    > > What's the RTT between the sender & receiver in your reproduction? Are you using bbr on the sender side?
    >
    >
    > 100ms RTT
    >
    > Which exact version of linux kernel are you using ?

    Thanks for testing this, Eric. Would you be able to share the MTU
    config commands you used, and the tcpdump traces you get? I'm
    surprised that receive buffer autotuning would work for advmss of
    around 6500 or higher.

    thanks,
    neal




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Download attachment "receiverconf" of type "application/octet-stream" (73007 bytes)

Download attachment "senderconf" of type "application/octet-stream" (73639 bytes)