Dashboards will display whatever matches your search criteria. 

For example, if you search for “CPE123 traffic” you see traffic graphs for all interfaces on device CPE123. 

If you want to see all graphs except traffic, you can use ! to exclude them, i.e. “CPE123 !traffic”. 

For traffic only for a specific interface on a specific device, you can use its Tag, which is the unique identifier for that specific interface. Tags can be found under Configuration -> Customer/Views -> Edit Mnemonics. In this case it will be something like "CPE123__Gi1/0”, or then "CPE123__Gi1/0 traffic” for traffic graphs only.