[Olsr-users] Does tc-prio really work as advertised?

[Sven-Ola Tuecke]

Hi,

you may investigate the olsr-prio script of the freifunk firmware. It works 
on kernel-2.4 but it's likely also OK on 2.6. Script ist located here:

http://ff-firmware.cvs.sourceforge.net/ff-firmware/ff-devel/freifunk-olsrd/etc/init.d/

// Sven-Ola

"Joerg Pommnitz" <(spam-protected)> schrieb im Newsbeitrag 
news:(spam-protected)
> Hello all,
> I might make a fool out of me, but I think the prio qdisc doesn't work as 
> advertised in any document I could lay my hands on.
>
> My problem was that the link quality reported by the olsr.org olsrd 
> degraded depending on the amount of payload traffic transferred through an 
> adhoc/mesh interface. The LQ is calculated from the packet loss of LQ 
> Hello packets sent through this interface. To make sure normal traffic 
> does not interfere with this value, olsrd sets the TOS field to 0x10 
> (Minimize-Delay) by default. This should give olsr traffic the highest 
> priority on the link.
>
> Investigating this issue I replaced the default Pfifo_fast with a prio 
> qdisc and attached a pfifo on each of the bands:
>
>    INTERFACE=wifi0
>    tc qdisc add dev $INTERFACE root handle 1: prio
>    tc qdisc add dev $INTERFACE parent 1:1 handle 10: pfifo
>    tc qdisc add dev $INTERFACE parent 1:2 handle 20: pfifo
>    tc qdisc add dev $INTERFACE parent 1:3 handle 30: pfifo
>
> The I used ping -Q TOSVALUE to send packets with different TOS values 
> through the interface. tcpdump confirmed the correct TOS values in the 
> outgoing packets.
>
> With "tc -s qdisc ls dev wifi0" I could observe the effects of the 
> different TOS values. The result: no effect at all! Every single packet 
> used the band indicated by the first value in the priomap (e.g. band 1 by 
> default, in my case the pfifo with handle 20:). I can't square this 
> observation with the available documentation.
>
> Looking at the source code, it seems that sched_prio uses the 
> skb->priority value to select the outgoing band. According to some 
> documentation I found, an application can set this value.
>
> Now I'm at a loss. I can work around this problem with filters, but I 
> don't think that this is the correct solution. Any suggestions?
>
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>
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