QoS - applying policies
When configuring QoS, simply classifying and marking will not enable any QoS mechanisms. Traffic will still be treated on a first come first serve basis, unless some QoS policy is applied to the marked traffic.
Such policies can come in the form of various mechanisms including shaping, policing, and various forms of queuing. But we must keep in mind that QoS mechanisms kick in only when there is congestion. Otherwise, traffic is served immediately.