Re: [PATCH net-next] net_sched: restore "mpu xxx" handling

[Kevin Bracey <kevin@bracey.fi>]

On 12/01/2022 08:36, Kevin Bracey wrote:
>
> Indeed, There has never been any kernel handling of tc_ratespec::mpu - 
> the kernel merely stored the value.
>
> The overhead had been similarly passed to the kernel but not 
> originally acted on. Linklayer had to be added to tc_ratespec. 

Ah, I need to correct myself there. The overhead was originally acted on 
in qdisc_l2t. htb_l2t forgot to incorporate it.

So:

  * overhead - always passed via tc_ratespec, handled by kernel. HTB
    temporarily ignored it.
  * linklayer - not originally passed via tc_ratespec, but incorporated
    in table. HTB temporarily lost functionality when it stopped using
    table. Later passed via ratespec, or inferred from table analysis
    for old iproute2.
  * mpu - always passed via tc_ratespec, but ignored by kernel.
    Incorporated in table. HTB lost functionality when it stopped using
    table.

("always" meaning "since iproute2 first had the parameter").

So this is a tad different from the other two - those were making the 
kernel act on something it previously acted on. This makes it act on 
something it's always been given, but never acted on. But it restores 
iproute2+kernel system functionality with no userspace change.

Kevin