[homenet] -CoDel

"David R. Oran" <daveoran@orandom.net> Fri, 15 March 2019 15:08 UTC

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From: "David R. Oran" <daveoran@orandom.net>
To: Toke Høiland-Jørgensen <toke=40toke.dk@dmarc.ietf.org>
Cc: Juliusz Chroboczek <jch@irif.fr>, Mikael Abrahamsson <swmike@swm.pp.se>, homenet@ietf.org
Date: Fri, 15 Mar 2019 11:08:37 -0400
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Subject: [homenet] -CoDel
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On 15 Mar 2019, at 8:34, Toke Høiland-Jørgensen wrote:

> Juliusz Chroboczek <jch@irif.fr> writes:
>
>>> PIE [...] lends itself better for implementation in existing 
>>> hardware,
>>> or hardware with small modification.
>>
>> Could one of you please explain why?
>
> With the caveat that I have never worked with any of this hardware, 
> this
> is my understanding:
>
> Basically, you can re-use the drop mechanism from RED and use the PIE
> algorithm as a (better) way to control the setpoints. This makes it
> possible to retrofit it in existing hardware. In fact I believe you 
> can
> implement PIE entirely in the (software) control plane on (a lot of)
> gear that already knows how to do RED.
>
Another factor, which as I recall was perhaps the strongest of the 
original motivations for PIE, is that PIE does nearly all its work on 
enqueue, whereas CoDel does most of its work on dequeue. In many 
hardware interfaces, especially at a head end where there are lots of 
queues and a simple hardware FIFO feeding the link, it turns out to be 
difficult/expensive to insert the computations CoDel does on each 
dequeue operation.

> -Toke
>
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DaveO