netdev - Re: [PATCH iproute2] htb: report overhead attribute

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Date:	Tue, 4 Jun 2013 13:11:47 +0200
From:	Jesper Dangaard Brouer <jbrouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Rick Jones <rick.jones2@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	netdev <netdev@...r.kernel.org>,
	"russell-tcatm@...art.id.au" <russell-tcatm@...art.id.au>
Subject: Re: [PATCH iproute2] htb: report overhead attribute

On Mon, 03 Jun 2013 08:56:02 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

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