[Cerowrt-devel] [Codel] [Bloat] FQ_Codel lwn draft article review

[Eric Dumazet]

On Wed, 2012-11-28 at 13:37 -0500, Michael Richardson wrote:
> >>>>> "Paul" == Paul E McKenney <paulmck at linux.vnet.ibm.com> writes:
>     Paul> You lost me on this one.  It looks to me like
>     Paul> net/sched/sch_fq_codel.c 
>     Paul> in fact does hash packets into flows, so FQ-CoDel is
>     Paul> stochastic in the 
>     Paul> the same sense that SFQ is.  In particular, FQ-CoDel can hash a thin
>     Paul> session into the same flow as a thick session, which really is the
>     Paul> birthday effect.
> 
> Silly question from someone who should read more code, but...
> if one is hashing the packet to pick a flow bucket, shouldn't this hash
> occur before any application of address/port translation. ? (NAT)
> 
> (Maybe I've just found out that IPv6 + CoDel will be a killer
> combination)
> 

Why would it be a killer ?

A NATed flow becomes another flow, with its own hash

A tunnel might have a problem, _if_ the hash would be computed on
elements found on the outer header.

But luckily, we do a complete flow dissection.

(Assuming the default fq_codel classification)