Lund Performance Solutions

MPE Subqueue Concepts
Chapter 2 explains the concept behind subqueues. Sections contained in Chapter 2 include:


The MPE dispatcher is the part of the operating system that is responsible for the orderly allocation of CPU time among processes. The priority of a process dictates when it gets use of the CPU. Processes using very little CPU resources are rewarded with higher processing priority. CPU-intensive processes are penalized—moved to a lower priority by the dispatcher. Since a CPU can process only one request at a time, processes that are assigned lower dispatcher priorities have to wait for higher priority processes.

Standard MPE Subqueues

The MPE operating system has five standard subqueues to which a process can be assigned: AS, BS, CS, DS, and ES (the "S" stands for "subqueue"). A process can be assigned to a subqueue by logon or function. Priority within a subqueue is defined by a numerical value ranging from 1 to 255; 1 is the highest priority, and 255 is the lowest.
  • The AS subqueue has the highest priority (1-98). It is reserved for highest priority operating system processes.
  • The BS subqueue is the next highest priority (100-150). It is typically reserved for other system processes and extremely high priority user processes.
  • The CS subqueue (priority 152--200) is the default subqueue for interactive sessions.
  • The DS subqueue (priority 202-238) is reserved for high priority batch jobs.
  • The ES subqueue (priority 240-253) is typically used for any other processes that are to run at the lowest priority behind all other processes.
  • The AS or BS subqueues are called linear subqueues. The priority of a process in a linear subqueue does not change during the life of the process. Once a process within the AS or BS subqueues is assigned a priority, the dispatcher does not change its priority. The priority remains static.
    The CS, DS, and ES subqueues are circular. In circular subqueues, a process starts off at a particular priority and then degrades as it uses more and more CPU time. When it reaches the limit of the subqueue (the lowest priority defined for that subqueue) it will do one of two things:
  • Remain there if the queue is configured to decay.
  • Return to the base (the highest point) of the subqueue if the subqueue is configured to oscillate.

  • NOTE The TUNE command in MPE can be used to specify whether a queue will decay or oscillate.

    Although it is possible to designate a process’ priority, the MPE dispatcher does not provide the ability to prioritize by user, application, program, LDEV, day of the week, time of day, job-only, session-only, batch, or session. This is where Q-Xcelerator provides greater control than MPE by allowing controlling process priority specific to all of the above mentioned criteria.

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