Re: [Codel] [Bloat] [Cerowrt-devel] FQ_Codel lwn draft article review

[David Lang <david@lang.hm>]

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On Tue, 27 Nov 2012, Jim Gettys wrote:

> 2) "fairness" is not necessarily what we ultimately want at all; you'd
> really like to penalize those who induce congestion the most.  But we don't
> currently have a solution (though Bob Briscoe at BT thinks he does, and is
> seeing if he can get it out from under a BT patent), so the current
> fq_codel round robins ultimately until/unless we can do something like
> Bob's idea.  This is a local information only subset of the ideas he's been
> working on in the congestion exposure (conex) group at the IETF.

Even more than this, we _know_ that we don't want to be fair in terms of the raw 
packet priority.

For example, we know that we want to prioritize DNS traffic over TCP streams 
(due to the fact that the TCP traffic usually can't even start until DNS 
resolution finishes)

We strongly suspect that we want to prioritize short-lived connections over long 
lived connections. We don't know a good way to do this, but one good starting 
point would be to prioritize syn packets so that the initialization of the 
connection happens as fast as possible.

Ideally we'd probably like to prioritize the first couple of packets of a 
connection so that very short lived connections finish quickly

it may make sense to prioritize fin packets so that connection teardown (and the 
resulting release of resources and connection tracking) happens as fast as 
possible

all of these are horribly unfair when you are looking at the raw packet flow, 
but they significantly help the user's percieved response time without making 
much difference on the large download cases.

David Lang

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