z/OS problem management
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Diagnosing a loop

z/OS problem management

This section contains a flowchart and steps to guide you through diagnosis of a loop.

The purpose of this section is to guide you through the diagnosis of a loop with these topics:
  • Overview of a loop
    A loop is a repetitive set of instructions being performed by a job or unit of work. A job or function that is looping can appear to be hung or can use a high amount of CP resource and lock out other work from getting service.
  • Gathering additional data for a loop
    There are various types of data to collect depending on the loop symptoms.
  • Analyzing the dump to determine the type of loop
    You will need to determine if you have an enabled or disabled loop.
  • Diagnosing a disabled loop
    Because disabled routines do not take interrupts, a disabled loop is not visible in the system trace output. Normally, a disabled loop results in a spin loop in a multiprocessor environment.
  • Diagnosing an enabled loop
    Enabled loops are often quite large and can include several distinct operations, such as I/O, SVCs, and module linkages. Because the loop is enabled, it is interrupted, preempted, and resumed many times. This makes the loop pattern difficult to recognize.
  • Diagnosing an excessive spin (spin loop)
    To avoid unnecessary recovery actions, system functions that can validly exceed the interval are exempt from excessive spin-loop processing, so that they will not cause any recovery actions. If they exceed the time-out interval, these system functions do cause an excessive spin loop record to write to the logrec data set.
  • Analyzing a logrec error record
    Analyze a logrec error record for a disabled loop.
  • Searching the problem reporting databases
    Search arguments for loops are used to search problem reporting databases.

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