VMS Help V73 Features, Programming Features, Performance API  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The Performance Application Programming Interface (API) provides
    a documented functional interface-the $GETRMI system service-that
    allows performance software engineers to access a predefined list
    of performance data items.

    For more information about $GETRMI, refer to the OpenVMS System
    Services Manual.