The SET SERVICES command enables the collection of system
    services data. After you enter the GO command with system
    services data collection enabled, the Collector intercepts every
    system service call in the user program and records it in the
    performance data file. For each call, the Collector records the
    name of the system service, the program location where it was
    called, and a CPU time stamp.

    You must collect stack PC information if you want to use a /MAIN_
    IMAGE, /CUMULATIVE or /STACK_DEPTH qualifier with the PLOT or
    TABULATE command in the Analyzer.