On Mon, 03 Jun 2013 08:56:02 -0700
Eric Dumazet [off-list ref] wrote:

On Mon, 2013-06-03 at 08:45 -0700, Rick Jones wrote:

quoted

Is it (still) possible to have a negative overhead?

http://www.linksysinfo.org/index.php?threads/speedmod-with-tc-atm-qos-patch-for-adsl.31541/

overhead always has been unsigned in the kernel.

What you describe is a userland hack in tc command.
(or a bug)

Rick is referencing Russell Stuart's patches, where a negative overhead
was possible.
 http://ace-host.stuart.id.au/russell/files/tc/tc-atm/#history

But my patches got accepted into the kernel, where a negative
overhead was not possible. In retrospect, we should have supported a
negative overhead.

A negative overhead *is* a valid use-case, and we should work towards
supporting this. E.g. by changing the recent added "u16 overhead" in
struct psched_ratecfg to be "s16" (ref [1]) ?


[1] commit 01cb71d2d47 (net_sched: restore "overhead xxx" handling)
 https://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=01cb71d2d47b78354358e4bb938bb06323e17498

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer