[Cerowrt-devel] Equivocal results with using 3.10.28-14

Dave Taht dave.taht at gmail.com
Mon Feb 24 11:47:31 EST 2014

On Mon, Feb 24, 2014 at 11:38 AM, Aaron Wood <woody77 at gmail.com> wrote:
> Rich,
> One thing that helped considerably on my my DSL link (21000/1200), was
> turning on the Link Layer Adaptation.  With that, and efq_codel, I've been
> very happy with the (nearly non-existent) latency.  Yeah, I lost a couple
> percent off the top, but the behavior is better.  Although I was starting
> from a much better base given that Free.fr's DSL modems already using either
> fq_codel or RED (I'm not sure the specifics, but I think Dave Taht's gotten
> them from Free.fr in the past).

Free deployed fq_codel on the revolution V6 box 1.5 years back. They
found it necessary to fiddle with the target, and shared with me
nearly all the details of their setup
and their formula for target, which I have embedded here:


despite testing a lot on your line we didn't do much better than they...

> Dave, the 40ms target is the buffer latency target?  or how often the drop
> rates are recomputed?

It is the starting point for the drop scheduler to start thinking
about dropping some packets.

>  or how often the drop
> rates are recomputed?

That's a RED or PIE -thinking way of looking at the problem,
recomputing a random number across a fixed interval.

the drop rates in codel are computed on a decreasing interval based on
a invsqrt control law that is much smoother than pie or red.

> -Aaron

Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html

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