Indeed fq_codel will work very well for many home users - especially where
the home user can be expected to be aware of apps that might be gaming the
system. If multiple homes are sharing a link it might not always work so well.
To construct an example where fair queueing works poorly, place a flow that
is trying to game the system (e.g. a download performed by a download
accelerator, launching multiple TCP streams for the single download) next
to a bunch of flows that are opaque (e.g. Several VoIP calls through a VPN).
Simon
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On April 14, 2015 9:01:55 AM Toke Høiland-Jørgensen <[email protected]> wrote:
Simon Barber <[email protected]> writes:
> One problem with fair queueing is that it can be gamed. By opening
> multiple flows you achieve unfair priority. Part of Codel or PIE's
> beauty is that they are blind to the traffic, only reacting to the
> externally visible characteristics. This stems from the question 'what
> is a flow?'. There is no easy answer to this question, so Codel and
> PIE intentionally avoid the question.
Sure, if we knew what the One True Queue Management Scheme that always
did the right thing was, we probably wouldn't be having this
conversation. :)
> Of course in many practical situations some simple assumptions about
> what a flow is do work, and in those situations fair queueing performs
> very well. It's important to keep in mind the limitations though. Fair
> queueing is not a panacea.
Well, my focus has primarily been "why does my internet suck so much and
what can I do to fix it". And for that (e.g. home type networks)
fq_codel is very close to a panacea.
I am well aware that there probably exists situations in which the
fq_codel assumptions do not hold up (and we do point out a couple in the
draft). However, I don't think I've ever seen someone actually
*demonstrate* (you know, with data) a scenario where fq_codel performs
worse than either Codel or PIE. If someone can point me to such a
demonstration I'll be happy to be proved wrong... :)
-Toke
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