[Codel] [Bloat] The challenge

[Kevin Gross]

The decision the algorithm is trying to make is when to drop packets. RED
drops packets when the maximum queue level rises. CoDel drops packets when
the minimum queue level rises. If the queue is never (nearly) empty, the
interface is oversubscribed and packet drops are in order. But because it
looks at minimum, not maximum, CoDel will not drop packets in bursts so
long as those bursts pass within the (5 ms) interval used to measure
minimum queue level.

1/sqrt bit controls how many packets get dropped as a function of time
and I gather it is control loop tuning used to strike a good balance
between responsiveness, stability and do no harm.

Kevin Gross

On Tue, May 8, 2012 at 7:04 PM, Dave Taht <dave.taht at gmail.com> wrote:

> Both the acm queue article and jim's blog entry this morning were way
> above mensa's standards.
>
> Nobody has attempted to explain the elegant simplicity of the
> algorithm itself in the inverse sqrt however!  I have a good grip on
> it, and am trying, but can barely explain it to myself. Anyone else
> care to dig through the codel code and try to put it into english?
>
> Nice bit in ReadWrite News:
>
>
> http://www.readwriteweb.com/enterprise/2012/05/good-news-for-solving-bufferbloat-codel-provides-no-knobs-solution.php
>
> Bob Cringley lays down the challenge for us here on the bloat list,
> and details the opportunity.
>
> http://www.cringely.com/2012/05/beginning-of-the-end-for-bufferbloat/
>
> He closes with:
>
> "My advice to Cisco, Netgear, D-Link and others is that this could be
> an important moment in their businesses if they choose to approach it
> correctly. It’s a chance to get all of us to buy new routers, perhaps
> new everything. Think of the music industry bonanza when we all
> shifted our record libraries from vinyl to CDs. It could be the same
> for networking equipment. But for that to happen the vendors have to
> finally acknowledge bufferbloat and use their marketing dollars to
> teach us all why we should upgrade ASAP. Everybody would win.
>
> Take our money, please."
>
> With the cerowrt project, at least, I've hoped to make that shift
> possible, and to some extent... happen.
>
> We have *working code*, and *proof of concept*. What's next? Where do
> we go from here?
>
> --
> Dave Täht
> SKYPE: davetaht
> US Tel: 1-239-829-5608
> http://www.bufferbloat.net
> _______________________________________________
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>
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