Re: [PATCH] net/sched: fq_codel: clamp flow deficit after quantum changes

[Eric Dumazet]

On Mon, Jun 8, 2026 at 5:39 PM Samuel Moelius
<sam.moelius@xxxxxxxxxxxxxxx> wrote:
>
> fq_codel updates the configured quantum without adjusting deficits for
> flows that are already active.  Those flows can continue to carry credit
> calculated under the old quantum.
>
> This can be observed by making a flow active, changing the quantum, and
> then dequeuing with the old deficit still present.
>
> Clamp active flow deficits to the new quantum when fq_codel's quantum
> changes so the new setting takes effect without waiting for stale credit
> to drain.
>
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@xxxxxxxxxxxxxxx>
> ---

This is not an issue, and we are trying to make the whole thing lockless.

Iterating trough the flows would require to hold qdisc spinlock for a
possibly very long time.

I vote against this change.