netdev - AW: Does tc-prio really work as advertised?

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Date:	Tue, 27 Nov 2007 02:54:10 -0800 (PST)
From:	Joerg Pommnitz <pommnitz@...oo.com>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	netdev@...r.kernel.org
Subject: AW: Does tc-prio really work as advertised?

Jarek,
this is all about outgoing packets, e.g. egress to use your word.
It doesn't matter whether the packets are originated locally or
whether the packets are forwarded from another host (I tried
both).

To restate the problem: according to my observations the prio qdisc
(and probably pfifo_fast, but I couldn't observe this) does not prioritize
at all and always uses the band indicated by the first entry in the
priomap.

By default the priomap looks like this:
qdisc prio 1: dev eth1 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1

there are 3 bands (1:1, 1:2 and 1:3). In theory the traffic should go through
the different bands according to the TOS value of the packets. My observation
is, that the traffic always uses the band pointed to by the first entry in the
priomap. This value is 1 by default, so all traffic goes through band 1:2.

Now it's entirely possible that I did something stupid, but nobody came forward
to show me the error of my ways (neither here nor on the lartc list).

-- Regards

       Joerg

----- Ursprüngliche Mail ----
Von: Jarek Poplawski <jarkao2@...pl>
An: Joerg Pommnitz <pommnitz@...oo.com>
CC: netdev@...r.kernel.org
Gesendet: Dienstag, den 27. November 2007, 10:58:38 Uhr
Betreff: Re: Does tc-prio really work as advertised?

On Tue, Nov 27, 2007 at 01:28:43AM -0800, Joerg Pommnitz wrote:
> Jarek,
> iptables chains (this is what I think you are referring to) are not  the issue.

Yes, but this could (wrongly) look like this according to my 1-st  message.

> This
> is about the qdisc that sits immediately over the device driver and  decides the
> order waiting packets are sent over the line/air/carrier pigeon/... .
> My suspicion is that skb->priority used to be set to a value that  derived from the
> TOS bits. Then something changed and nobody noticed.

I'm not sure of your problem: did you try this on a box which
gets packets with TOS set earlier, does forwarding, and uses this
prio on egress? If so, and this doesn't work, then you are right
something could be wrong.

Regards,
Jarek P.

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