[Cake] dual-src/dsthost unfairness, only with bi-directional traffic

[Toke Høiland-Jørgensen]

Jonathan Morton <chromatix99 at gmail.com> writes:

>>> Yes, exactly. Would be interesting to hear what Jonathan, Toke and
>>> others think. I want to see if fairness is preserved in this case with
>>> sparse flows only. Could flent do this?
>> 
>> Well, sparse flows are (by definition) not building a queue, so it
>> doesn't really make sense to talk about fairness for them. How would you
>> measure that?
>> 
>> This is also the reason I agree that they shouldn't be counted for host
>> fairness calculation purposes, BTW...
>
> The trick is that we need to keep fairness of the deficit
> replenishments, which occur for sparse flows as well as bulk ones, but
> in smaller amounts. The number of active flows is presently the
> stand-in for this. It's possible to have a host backlogged with
> hundreds of new flows which are, by definition, sparse.

Right, there's some care needed to ensure we don't get weird behaviour
during transients such as flow startup.

> I'm still trying to get my head around how the modified code works in
> detail.  It's possible that a different implementation would either be
> more concise and readable, or better model what is actually needed.
> But I can't tell until I grok it.

Cool, good to know you are on it; I'm happy to wait until you've had
some time to form an opinion on this :)

-Toke