give priority to icmp

We have a pretty crowd network right now.
I’m starting to think about give priority to the different kind of traffic.

I don’t have a masqueraded net so I don’t need to mark the connection.
The first thing that I did was to mangle the traffic, then to build the queue tree.

Now I have the queue working I see the statistics flowing but I don’t see the effect of the priority I gave to the icmp packets. In fact when I send a big mail the ping latency skyrocket to 1500-2000ms

Was someone able to manage a similar situation?
thanks

This http://www.faqs.org/docs/Linux-HOWTO/ADSL-Bandwidth-Management-HOWTO.html help for me!