Collector Command

    Enables the collection of program counter sampling data with the
    sampling interval based on process CPU (or virtual) time.

    Format

      SET CPU_SAMPLING

1  –  Description

    The SET CPU_SAMPLING command causes PCA to collect PC values
    in the same way that SET PC_SAMPLING does, with one important
    exception. The CPU sampling interval is based on virtual process
    or CPU time, not system time. When you issue the SET CPU_SAMPLING
    command, PCA will only collect PC values whenever there has been
    one or more clock ticks on the process's clock.

    There are many external factors that can affect the behavior
    of a program, in relation to the system (or wall) clock. For
    example, page faulting and system service wait time (including
    I/O wait time). These conditions make it difficult to determine
    whether the program counter contains a specific location because
    of the structure of the program's algorithm or because of other
    operations occuring in that interval. Under these conditions,
    sampling the PC values based on the process's CPU time would be
    more effective and reproducible, because the effects caused by
    contending processes are reduced.

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

2  –  Qualifiers

2.1    /INTERVAL

       /INTERVAL:n

    Specifies the sampling interval in milliseconds. The value of n
    must be at least 10 milliseconds and at most 60,000 milliseconds.
    Because the granularity of the system clock is 10 milliseconds,
    you should use a multiple of 10. The default sampling interval is
    10 milliseconds; therefore, you can use the /INTERVAL:n qualifier
    only to specify a longer sampling interval.

2.2    /STACK_PCS

    Specifies that stack PC values are collected for CPU data.
    Further CPU_SAMPLING requests will assume a default of /STACK_
    PCS. This is the default upon entry into the Collector.

2.3    /NOSTACK_PCS

    Specifies that no stack PC values are collected for CPU data.

3  –  Examples

  PCAC> SET CPU_SAMPLING/INTERVAL=20/NOSTACK_PCS

      This command causes the interval to be 20 milliseconds, and
      disables STACK_PCS collection for this measurement. For all
      further SET CPU_SAMPLING requests, a default of /NOSTACK_PCS
      will be assumed.