[Codel] [PATCH 1/2] codel: Controlled Delay AQM

[Eric Dumazet]

On Mon, 2012-05-07 at 15:36 -0400, Jim Gettys wrote:

> I think it is safe for it to behave the rest of the way Linux ECN
> support does right now: it only gets used if the peer requests it.
> 
> Not clear to me there needs to be/should be any option at all: the last
> conversation I had with Steve Bauer was that something north of 20% of
> conversations were ECN capable. Is there one for the other instances of
> ECN support in Linux?  If so, it should be keyed by the same variable,
> and not be a one-off for codel.
> 

SFB, one of the latest qdisc added in linux has ECN support enabled.

There is no option to disable it, because I felt it was safe. Maybe I
was a fool, but problem is I am not sure SFB is even used.

> If you wanted to test ECN separately from drop with codel, then you'd
> just request ECN in the conversation (by default, OS's don't normally
> request ECN today, as the remaining brokenness gets sorted out).

Since ECN is not mentioned in Codel paper, this means no simulation was
done to study the possible effects.

So its probably better to leave ECN as an option. We can change the
default later.