[Codel] How to make a bufferbloat fairqueue with tc qdisc

Anirudh Sivaraman sk.anirudh at gmail.com
Thu Dec 5 15:36:57 EST 2013

On Thu, Dec 5, 2013 at 2:52 PM, Dong Mo <montedong at gmail.com> wrote:
> Dear List,
> I am trying to make a bufferbloat fairqueue with qdisc and compare that with
> fq_codel.
> However, I am now having some hard time doing it.
> The commands I am using are:
> tc qdisc add dev $IFACE root handle 1: htb default 1
> tc class add dev $IFACE parent 1: classid 1:1 htb rate 40mbit
> tc qdisc del dev eth4 parent 1:1 handle 10: sfq perturb 10
> And sending packet from the sender, where sfq qdisc is set, to the receiver,
> the queuing delay is quite small and is approximately the same as when
> fq_codel enabled.
> However, if I am not using sfq (only htb set), and send only one flow over
> this link, the delay will explode again.
> So is sfq here cut off the queue length somehow? How should I make a
> bufferbloat fair queue on linux box using tc qdisc?

You could start with the fq_codel qdisc and set the codel interval and
target parameters to absurdly large values (say 1000 seconds each) to
simulate a qdisc that has fair queuing but almost never drops a


> Thanks
> -Mo Dong
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