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

Eric Dumazet <eric.dumazet@gmail.com> Sat, 03 December 2016 23:09 UTC

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From: Eric Dumazet <eric.dumazet@gmail.com>
To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Sat, 03 Dec 2016 15:09:21 -0800
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References: <CADVnQymCmQ_MWSRcd+Y4=pgf3Shqnw5SfXrAkjonj+UFqtBrdA@mail.gmail.com> <20161202224006.GA5065@sesse.net> <1480721486.18162.392.camel@edumazet-glaptop3.roam.corp.google.com> <CADVnQym9iPJ+GR7BN9fPRe3on_j=OxUD0D83DS6Dzf1xLKvtnA@mail.gmail.com> <20161203191353.GA972@sesse.net> <1480796415.18162.408.camel@edumazet-glaptop3.roam.corp.google.com> <9A821B94-143B-446F-8852-2EB0158DD57C@gmail.com> <1480799260.18162.418.camel@edumazet-glaptop3.roam.corp.google.com> <20161203213428.GB38041@sesse.net> <1480801837.18162.419.camel@edumazet-glaptop3.roam.corp.google.com> <20161203221338.GC38041@sesse.net> <1480805737.18162.425.camel@edumazet-glaptop3.roam.corp.google.com> <1480806161.18162.429.camel@edumazet-glaptop3.roam.corp.google.com>
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Cc: Jonathan Morton <chromatix99@gmail.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 15:02 -0800, Eric Dumazet wrote:
> On Sat, 2016-12-03 at 14:55 -0800, Eric Dumazet wrote:
> 
> > Perfect.
> > 
> > Note that starting from linux-4.4, e1000e gets gro_flush_timeout that
> > would help this precise workload
> 
> Also it appears the sender uses a lot of relatively small segments (8220
> bytes at a time), with PSH, so GRO wont be able to help.
> 
> I wonder how these PSH are forced.

One possibility would be that the sender is not using fq/pacing,
or some driver is using skb_orphan(), killing TCP Small queue.

-> No pressure on qdisc, auto corking does not trigger,
and application does small writes.

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