[Cake] Re: [PATCH net-next v7 1/4] net/sched: cake, fq_codel: return the classifier result to the caller

[Jamal Hadi Salim <jhs@mojatatu.com>]

On Mon, Oct 19, 2026 at 2:11 PM Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>
> Jamal Hadi Salim <jhs@mojatatu.com> writes:
>
> > The Fix:
> > cake and fq_codel run an optional external classifier from their enqueue
> > path and then compute the flow hash inside the helper. Have the helper
> > return the filter's overrides (cake) or a 1-based flow index or a request
> > to hash (fq_codel) instead, so the caller owns the flow selection.
> >
> > This is preparation for the accounting changes that follow. Packet
> > classification and flow selection are unchanged.
>
> It's not clear to me why this change is needed at all for fq_codel?
> fq_codel_hash just does a reciprocal_scale() of the skb hash, it doesn't
> mutate any qdisc state. So why can't fq_codel_classify not just stay as
> it is?

It is not functionaly needed for fq_codel, it is more because these
two are cousins and simplifies subsequent patches.
Note in patch 4 we force the same semantics on cake as in fq_codel
(classifier decides the drop, the caller owns flow selection). Keeping
fq_codel's classify the same makes patch 3 hunks in the two files
similar. There is another reason: the old helper encoded "drop" as a
magic return and carried the 1-based +1 arithmetic on every return
path.
In any case, unless you feel strongly i would rather keep it.

cheers,
jamal