The switch by default map according to vlan priority. If traffic received with the same vlan priority it will all be mapped to single egress queue and will be handle as fifo.
If they want to map according to dscp they need to change the trust mode on the ingress ports to L3. With this mode there is default mapping of dscp to switch priority SP ,where dscp 0-7 are mapped to SP0 which is mapped to traffic class 0 , 8-15 mapped to tc1 and so forth .
You can see the mapping and trust mode with show qos interface eth command and you can also modify it with interface eth qos ... commands.
Thank you very much!