[Codel] fq_codel_drop vs a udp flood

[Eric Dumazet]

On Sat, 2016-04-30 at 20:41 -0700, Dave Taht wrote:
> >>>
> >>>     45.78%  [kernel]       [k] fq_codel_drop
> >>>      3.05%  [kernel]       [k] ag71xx_poll
> >>>      2.18%  [kernel]       [k] skb_release_data
> >>>      2.01%  [kernel]       [k] r4k_dma_cache_inv
> 
> The udp flood behavior is not "weird".  The test is wrong. It is so filling
> the local queue as to dramatically exceed the bandwidth on the link.

Well, just _kill_ the offender, instead of trying to be gentle.

fq_codel_drop() could drop _all_ packets of the fat flow, instead of a
single one.

It is too cpu intensive to be kind to the elephant, since under pressure
fq_codel_drop() needs to be called for every enqueue.

Really, we should not try to let inelastic flows hurt us.

I can provide a patch.