From DD-WRT Wiki
The definitive tc manpage.
A good wonder shaper explanation this also includes a good explanation of why qos does not work until you set the uplink and downlink values to slightly below your connections actual values. This is the most common reason QoS does not work.
A common request is Rate limiting a single host or netmask
This user guide is a good read in limiting/shaping the total bandwidth of the network.