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Re: [aqm] RED implementation on Linux 3.14.22

Jim Gettys <jg@freedesktop.org> Mon, 15 December 2014 13:41 UTC

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Date: Mon, 15 Dec 2014 08:41:45 -0500
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From: Jim Gettys <jg@freedesktop.org>
To: Simone Ferlin-Oliveira <ferlin@simula.no>, Toke Høiland-Jørgensen <toke@toke.dk>, Dave Taht <dave.taht@gmail.com>
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Subject: Re: [aqm] RED implementation on Linux 3.14.22
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On Mon, Dec 15, 2014 at 2:51 AM, Simone Ferlin-Oliveira <ferlin@simula.no>
wrote:
>
> All,
>
> I am doing some work with shared bottleneck detection that requires
> some evaluation with different AQM, in particular, RED. Since I
> haven't been following the evolution of the implementation,  I would
> like to ask about your experience with the code on Linux 3.14 (and
> newer).
>

​I know that Dave Taht ran into bugs in RED a while back, which I believe
have been fixed for quite a while.

You should always be looking at whether code has been patched in the
current kernel.org system for a module like that you are interested in, so
do a diff between 3.14 and the current Linux system. 3.14 is recent enough
that it may be viable for experiments, for the time being.  Planning to
keep up with Linux development is wise long term in any case, as the rate
of improvement/change in the networking stack is very high at the moment as
draining the bufferbloat swamp and other performance work continues.

Also note that underlying device drivers may have (sometimes lots) of
buffering out of control of the Linux queue discipline.  For Ethernet
devices, you should ensure that that the drivers have BQL support
implemented to minimize this buffering.  Other classes of drivers are more
problematic, and may have lots of buffering to surprise you.

Also be aware that ethernet flow control may move the bottleneck from where
you expect to somewhere else, and that switches in networks also have to be
well understood.  Most consumer switches have this *on* by default, and
mixed 1G/100Mb networks can be particularly "entertaining" in this regard.
Cable modems, unfortunately, typically do not implement flow control, but
some DSL modems do (putting the bottleneck into your router, rather than in
the modem).


> *Any* help is appreciated.
>

​Hope this helps.
​


>
> Thanks,
> Simone
>
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