[Codel] fq_codel_drop vs a udp flood

[Roman Yeryomin]

On 1 May 2016 at 20:59, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> 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.
>

So if I run some UDP download you will just kill me? Sounds broken.

Regards,
Roman