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Message-ID: <20130604131147.2d357322@redhat.com>
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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