[LARTC] HTB traffic shaping odd effects

[Oliver Hookins]

Hi,

I'm trying to perform some (what I consider) basic traffic shaping on 
our network utilising HTB. I have mostly reused the example on the 
lartc.org site:

tc qdisc add dev eth0 root handle 1: htb default 10
tc class add dev eth0 parent 1: classid 1:1 htb rate 100mbit burst 24k
tc class add dev eth0 parent 1:1 classid 1:10 htb rate 50mbit ceil
80mbit burst 19k
tc class add dev eth0 parent 1:1 classid 1:20 htb rate 1mbit ceil
1mbit
tc qdisc add dev eth0 parent 1:10 handle 10: sfq perturb 10
tc qdisc add dev eth0 parent 1:20 handle 20: sfq perturb 10
tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip src
X.X.X.X flowid 1:20

So we have a total of 100mbit to be used, the default class 1:10 gets 
50mbit and a ceiling of 80mbit whereas my test host X.X.X.X gets only 
1mbit in any situation. Some rate limiting is definitely happening, but 
I am finding the outbound traffic is limited to 2mbit instead of 1mbit. 
If I change the rate (to say 10mbit) the outbound traffic gets up to 
again twice the rate (in this case 20mbit).

Any thoughts? I have had a look at the tc statistics but it doesn't 
appear as I would expect it to. Class 1:10 shows a lot of dropped 
packets but it is only averaging around 30mbit constantly. On the other 
hand class 1:20 doesn't show any dropped packets. Similarly there are no 
packets marked as overlimit for any class. I occasionally see the tokens 
for 1:20 go negative... everything is quite strange.

Any help would be appreciated.

-- 
Regards,
Oliver Hookins