[Bloat] tc linklayer ADSL calc broken after commit 56b765b79 (htb: improved accuracy at high rates)

[Eric Dumazet]

On Wed, 2013-05-29 at 15:13 +0200, Jesper Dangaard Brouer wrote:
> I recently discovered that the (traffic control) tc linklayer
> calculations for ATM/ADSL have been broken by:
>  commit 56b765b79 (htb: improved accuracy at high rates).
> 
> Thus, people shaping on ADSL links, using e.g.:
>  tc class add ... htb rate X ceil Y linklayer atm overhead 10
> 
> Will no-longer get ATM cell tax/overhead adjusted.
> 
> How can we solve/fix this?
> Perhaps we can change to use the "stab" system instead (as it does
> not seem to be broken by the commit).
> 
> But how do we facilitate a change to use "stab" system (for all the
> scripts using the old option)?
> 
> Can we change the iproute2/tc command to handle this transparently, or
> should we give an error/warning if someone uses "tc" and "linklayer" on
> a kernel above v.3.8. ?
> 
> 
> History:
>  - My linklayer ATM changes appeared in kernel 2.6.24 (and iproute2 2.6.25)
>  - The STAB changes appeared in kernel 2.6.27
> 

Hi Jesper

stab suffers from the same problem : its table driven, so works only for
packet smaller than a given size.

I am not sure it will solve the ATM logic (with the 5 bytes overhead per
48 bytes cell)

btw, even on old kernels :