netdev - Re: Linux ECN Handling

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Message-ID: <CADVnQymoGNgVZP+gXmdKCPVihrWo+J8LQJV9_fmyj3f8mhMRtQ@mail.gmail.com>
Date:   Fri, 1 Dec 2017 11:35:30 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Steve Ibanez <sibanez@...nford.edu>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>, Florian Westphal <fw@...len.de>,
        Mohammad Alizadeh <alizadeh@...il.mit.edu>,
        Lawrence Brakmo <brakmo@...com>
Subject: Re: Linux ECN Handling

On Mon, Nov 27, 2017 at 1:49 PM, Steve Ibanez <sibanez@...nford.edu> wrote:
>
> Hi Neal,
>
> I tried out your new suggested patches and indeed it looks like it is
> working. The duration of the freezes looks like it has reduced from an
> RTO to 10ms (tcp probe reports SRTT measurements of about 200us just
> before the freeze). So the PTO value seems to be correctly set to
> max(2*SRTT, 10ms).

Great. Thank you for testing this!

Our team will look into testing these patches more and sending some
version of them upstream if things look good.

Also, BTW, in newer kernels, with bb4d991a28cc ("tcp: adjust tail loss
probe timeout") from July, the TLP timeout should be closer to 2*SRTT
+ 2 jiffies, so if your kernel has 1ms jiffies this should further
improve things.

Thanks,
neal