Library /sys$common/syshlp/pca$help.hlb SET, VCPU_SAMPLING, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The SET VCPU_SAMPLING Collector command enables the collection
    of PC values for random vector instructions. The collected data
    lets you determine the scalar/vector parallelism throughout your
    entire program.

    When you collect vector CPU samples, the sampling interval timer
    includes only the time that the program is actually running
    the processor. This form of sampling allows you to focus on the
    particular areas of the program's algorithm where time is being
    spent, and not on the areas where outside influences consume
    time.