Abstract: A data processing system includes host computers and a data storage system that (1) periodically calculates port congestion values for storage system ports based on per-port values for (a) a number of storage IO commands being processed by each port and (b) CPU utilization of one or more CPUs assigned to each port, and (2) periodically sends the port congestion values to the host computers. Each host computer includes multipathing logic for selectively directing storage IO commands on selected paths to the data storage system. The multipathing logic receives the port congestion values from the data storage system and utilizes the port congestion values for path selection by preferentially directing first storage IO commands of higher service level objective to storage system ports having lower congestion and preferentially directing second storage IO commands of lower service level objective to storage system ports having higher congestion.