With polling Data Sources such as Modbus, BACnet, SNMP, etc. you can easily check the performance under the Runtime status when editing a Data Source.
The Poll duration tells you how long each poll takes to complete to retrieve your data. A poll will be discarded if the poll times take longer than your poll period. For example if you have a Modbus Data Source polling at 1 second and your poll time takes 1.5 seconds a poll will be discarded. It is good practice to have your poll times greater than the Poll duration. It is also best practice to have your time out x retries to be less than your poll time.