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Re: [aqm] [Bloat] TCP BBR paper is now generally available

Eric Dumazet <eric.dumazet@gmail.com> Sat, 03 December 2016 21:07 UTC

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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jonathan Morton <chromatix99@gmail.com>
Date: Sat, 03 Dec 2016 13:07:40 -0800
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Cc: "Steinar H. Gunderson" <sgunderson@bigfoot.com>, Neal Cardwell <ncardwell@google.com>, "aqm@ietf.org" <aqm@ietf.org>, bloat <bloat@lists.bufferbloat.net>
Subject: Re: [aqm] [Bloat] TCP BBR paper is now generally available
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On Sat, 2016-12-03 at 22:26 +0200, Jonathan Morton wrote:
> > On 3 Dec, 2016, at 22:20, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > 
> > Huge ACK decimation it seems.
> 
> That extract does not show ACK decimation.  It shows either jumbo
> frames or offload aggregation in a send burst, and ordinary
> delayed-acks each covering at most two packets received.  Nothing
> particularly weird or unusual appears to be happening in the network.

I do not attend IETF meetings so maybe my words are not exact.

What I meant was that we receive ACKS in bursts, with huge gaps between
them.

Look at tsval/tsecr, and that all ACKS are received in a 20 usec time
window, covering data that was sent in a 5 ms window.

Looks the reverse path is severely congested or a device does ack
filtering.

11:14:05.468643 IP6 C > S: Flags [.], ack 364280308, win 23430, options [nop,nop,TS val 864456877 ecr 3498315454], length 0
11:14:05.468645 IP6 C > S: Flags [.], ack 364288528, win 23407, options [nop,nop,TS val 864456877 ecr 3498315454], length 0
11:14:05.468646 IP6 C > S: Flags [.], ack 364296748, win 23415, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.468648 IP6 C > S: Flags [.], ack 364302460, win 23400, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.468650 IP6 C > S: Flags [.], ack 364304968, win 23430, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
<huge gap>
11:14:05.510870 IP6 C > S: Flags [.], ack 364313188, win 23407, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.510885 IP6 C > S: Flags [.], ack 364321408, win 23415, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.510888 IP6 C > S: Flags [.], ack 364328548, win 23396, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.510890 IP6 C > S: Flags [.], ack 364335340, win 23419, options [nop,nop,TS val 864456877 ecr 3498315455], length 0
11:14:05.510892 IP6 C > S: Flags [.], ack 364337848, win 23430, options [nop,nop,TS val 864456877 ecr 3498315456], length 0
11:14:05.510894 IP6 C > S: Flags [.], ack 364353208, win 23389, options [nop,nop,TS val 864456877 ecr 3498315456], length 0
11:14:05.510895 IP6 C > S: Flags [.], ack 364362508, win 23411, options [nop,nop,TS val 864456877 ecr 3498315456], length 0
11:14:05.510897 IP6 C > S: Flags [.], ack 364370728, win 23415, options [nop,nop,TS val 864456877 ecr 3498315456], length 0
11:14:05.510899 IP6 C > S: Flags [.], ack 364378948, win 23419, options [nop,nop,TS val 864456877 ecr 3498315456], length 0
11:14:05.510900 IP6 C > S: Flags [.], ack 364384660, win 23404, options [nop,nop,TS val 864456877 ecr 3498315457], length 0
11:14:05.510902 IP6 C > S: Flags [.], ack 364387168, win 23430, options [nop,nop,TS val 864456877 ecr 3498315457], length 0
11:14:05.510904 IP6 C > S: Flags [.], ack 364394308, win 23411, options [nop,nop,TS val 864456877 ecr 3498315457], length 0
11:14:05.510905 IP6 C > S: Flags [.], ack 364403608, win 23411, options [nop,nop,TS val 864456877 ecr 3498315457], length 0
11:14:05.510907 IP6 C > S: Flags [.], ack 364411828, win 23419, options [nop,nop,TS val 864456878 ecr 3498315457], length 0

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