[Codel] fq_codel_drop vs a udp flood

[Jonathan Morton]

> On 1 May, 2016, at 20:59, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> 
> fq_codel_drop() could drop _all_ packets of the fat flow, instead of a
> single one.

Unfortunately, that could have bad consequences if the “fat flow” happens to be a TCP in slow-start on a long-RTT path.  Such a flow is responsive, but on an order-magnitude longer timescale than may have been configured as optimum.

The real problem is that fq_codel_drop() performs the same (excessive) amount of work to cope with a single unresponsive flow as it would for a true DDoS.  Optimising the search function is sufficient.

 - Jonathan Morton