From NBSWiki

Problems

Don't trust the web interface, most settings don't work:
http://www.dd-wrt.com/wiki/index.php/Quality_of_Service#How_Do_You_Check_What_QoS_Priorities_Were_Applied

In short

• use HTB only
• use MAC or IP address (port doesn't work)
• Reboot for a real application of settings.

useful commands

From the above mentionned link

cat /proc/net/ip_conntrack

Look at 'mark' and it means the following:

   * Exempt: 100
   * Premium: 10
   * Express: 20
   * Standard: 30
   * Bulk: 40
   * (no QoS matched): 0 

I use this to check a specific host:

cat /proc/net/ip_conntrack|grep '192.168.0.10'