Re: Help about a QoS configuration

["Javier Ors" <jaorani@xxxxxxxxx>]

Ahh OK embedded. There may be hope then. I know that TI AR7 based
routers don't have a buffer beyond the device. The one I tested didn't
have any qdiscs built in apart from TIs prio/wrr, but it did work
without any rate limiting.

Then I am a lucky guy, this is mine:
http://wiki.openwrt.org/OpenWrtDocs/Hardware/D-Link/DSL-G624T
I didn't looked for it, it was just the one that the ISP gave to me with the connection. I was quite surprised when I realized that it was ssh-accesible, and even more when I checked that it has htb, cbq, sfq, prio, and even red with ecn. It seems that I recieved a good machine after all. As you see they are trying to port OpenWrt to it, if they got it maybe it'll be possible to apply russell's patches.

The buffer that I was talking about would not have been the 100
txqueuelen, but would have filled up before any packets got queued in that.

 

Was latency OK? If you can put a simple prio on the device with ICMP
(and I suppose arp to be safe since your connection is bridged) to high
band and all other to low, flood it with data and you still get good
latency then there isn't much of a buffer beyond the device.

Thanks again for all the info, luckily it's not the case, the latency is no more penalized than 20 ms in this situation, so it's ok, no buffers.
Just a question anyway...let's suppose that we have big buffers in the device and this penalize the latency, Would this buffers also prevent from shaping with a simple prio?  As I undertand, they shoudn't as long as any packet gets dropped between the qdisc and the device buffers, they would just fill up and then the queue would propagate to the qdisc, where the packet drop and the shaping should be done. Is this not the case for all drivers/interfaces?
 

Yes I suppose that should be OK as long as the % wasn't too high.

I have also observed this behaviour but I hardly undertand it. HTB works well only if you set a rate some % smaller than the congestion rate, then when you see tc -s class show, all the classes have relatively large queues (backlogged packets), and the shaping is smooth. But if you set the rate closer to the congestion rate (or higher)  then you start to see empty queues in the classes and/or with few backlogged packets. 
I can undertand this happening in a LAN, but not in the adsl modem interface, theoretically the interface won't dequeue packets at a higer rate that it can send them. So the queues should form anyway in the classes whatever high rate you set to the root class... Otherwise neither HTB nor the prio class would work without rate limiting (like in a LAN), so I don't understand why in this case it works for the prio but not for HTB.

Thanks again for your help and time, and please don't feel forced to answer. I can live with this doubts, it's not a matter of life or death...
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