[Codel] fq_codel_drop vs a udp flood

[Eric Dumazet]

On Thu, 2016-05-05 at 19:25 +0300, Roman Yeryomin wrote:
> On 5 May 2016 at 19:12, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> > On Thu, 2016-05-05 at 17:53 +0300, Roman Yeryomin wrote:
> >
> >>
> >> qdisc fq_codel 0: dev eth0 root refcnt 2 limit 1024p flows 1024
> >> quantum 1514 target 5.0ms interval 100.0ms ecn
> >>  Sent 12306 bytes 128 pkt (dropped 0, overlimits 0 requeues 0)
> >>  backlog 0b 0p requeues 0
> >>   maxpacket 0 drop_overlimit 0 new_flow_count 0 ecn_mark 0
> >>   new_flows_len 0 old_flows_len 0
> >
> >
> > Limit of 1024 packets and 1024 flows is not wise I think.
> >
> > (If all buckets are in use, each bucket has a virtual queue of 1 packet,
> > which is almost the same than having no queue at all)
> >
> > I suggest to have at least 8 packets per bucket, to let Codel have a
> > chance to trigger.
> >
> > So you could either reduce number of buckets to 128 (if memory is
> > tight), or increase limit to 8192.
> 
> Will try, but what I've posted is default, I didn't change/configure that.

fq_codel has a default of 10240 packets and 1024 buckets.

http://lxr.free-electrons.com/source/net/sched/sch_fq_codel.c#L413

If someone changed that in the linux variant you use, he probably should
explain the rationale.