[LARTC] icmp latency question

[Andrew Beverley]

 >> Our company's main line is quite busy the whole day and my shaping is
 >> working perfect, however even if I give icmp priority the pings still
 >> jump around quite a bit.

 > Sorry, I don't want to offend you, but your mail has been the cause for
 > the first good laugh of the day.

It may have been a stupid question, but it does raise an issue I have noticed. Even if I 
give maximum priority to SSH/ICMP, I notice that the latency does still jump around. Is 
this because I've not set up the queueing discipline very well?

For SSH I have:
tc class add dev imq0 parent 1:1 classid 1:10 htb rate 50kbit ceil 800kbit prio 1
tc qdisc add dev imq0 parent 1:10 handle 10: sfq perturb 10
tc filter add dev imq0 parent 1:0 prio 0 protocol ip handle 10 fw flowid 1:10

For other traffic I increase prio number and flowid. e.g:
tc class add dev imq0 parent 1:1 classid 1:40 htb rate 90kbit ceil 600kbit prio 4
tc qdisc add dev imq0 parent 1:40 handle 40: sfq perturb 10
tc filter add dev imq0 parent 1:0 prio 0 protocol ip handle 40 fw flowid 1:40

The parent is:
tc qdisc add dev imq0 root handle 1: htb default 40