Re: [LARTC] ATTN Andreas Klauer: ASCII art + comments, please?

[Andreas Klauer <Andreas.Klauer@metamorpher.de>]

On Sun, Mar 05, 2006 at 02:33:17PM -0800, gypsy wrote:
> Since I understand your ASCII art and comments, I would very much
> appreciate it if you would draw what you see and criticize the
> following.  Hopefully I'll better understand after that!

Uh, right. Don't take anything I say for granted, though.

> tc qdisc add dev imq0 root handle 1: htb default 20
> 
> tc class add dev imq0 parent 1: classid 1:2 htb rate 4522kbit ceil \
>    4760kbit burst 16k cburst 16k quantum 1500
> 
> tc class add dev imq0 parent 1:2 classid 1:1 htb rate 4522kbit ceil \
>    4760kbit burst 16k cburst 16k
> 
> tc class add dev imq0 parent 1:1 classid 1:10 htb rate 2487kbit \
>    ceil 4760kbit burst 16k cburst 16k quantum 1500 prio 1
> 
> tc class add dev imq0 parent 1:1 classid 1:20 htb rate 2034kbit \
>    ceil 4341kbit burst 10k cburst 16k quantum 1500 prio 4

First, here is what I see:

1: HTB root qdisc (default 20)
|
\--- 1:2 HTB root class (4522kbit/4760kbit)
     |
     \--- 1:1 HTB class (4522kbit/4760kbit)
          |
          \--- 1:10 HTB leaf class (2487kbit/4760kbit)
          \--- 1:20 HTB leaf class (2034kbit/4341kbit)

Now on to the criticising; the root class has a higher ceil than rate. 
However, different rate/ceil makes only sense if there is someone to 
borrow bandwidth from, which is not the case here. The root class 
acquires bandwidth directly from the QDisc, which has unlimited resources, 
as the root class itself is supposed to be the limiting factor. So what 
you have here should practically be no different from a 4760kbit class.

The 1:1 class seems to be useless; it has exactly the same settings 
as it's parent, except for quantum, which is not explicitely set. 
Furthermore, it does not have any siblings. Does not make sense to 
me as such a class will just use exactly the same rate as it's parent. 
Compare the statistics of these two classes below.

> class htb 1:1 parent 1:2 rate 4522Kbit ceil 4760Kbit burst 16Kb cburst
> 16Kb 
>  Sent 7826237 bytes 27128 pkts (dropped 0, overlimits 0) 
>  rate 1728bit 4pps 
>  lended: 1954 borrowed: 0 giants: 0
>  tokens: 39532 ctokens: 37555
> 
> class htb 1:2 root rate 4522Kbit ceil 4760Kbit burst 16Kb cburst 16Kb 
>  Sent 7826237 bytes 27128 pkts (dropped 0, overlimits 0) 
>  rate 1728bit 4pps 
>  lended: 0 borrowed: 0 giants: 0
>  tokens: 39532 ctokens: 37555

As for the leaf classes, their rates are fine (add up to the parent 
class rate), except that the parent actually can use 4760kbit rate
rather than 4522kbit. Their priorities are questionable; using 1 and 4 
here should not be any different from 1 and 2 or 3 and 6 or 0 and 1. 

It's one high- and one low-priority class either way. I would probably 
set a priority just for the low priority class, so that it becomes 
more obvious what is intended by this setting here.

That what you wanted?

Regards
Andreas Klauer
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