FMS Hardware Parameter ISCOPE

Data Type

Integer

Default Value

0

DESCRIPTION:

This parameter is used to adjust the scheduling and priority of the threads. The values are platform specific. Generally, you should not adjust these values. The values are bit flags. You may select any appropriate combination.

• 0 (default)
  All threads have the same priority and run in process scope.
• +1 (SGI)
  The priority of the CPU children is decreased by 1. The objective is to run them at a lower priority than the I/O threads.
• +2 (SGI)
  Run the I/O threads at a real time priority of 41. This assures that they are scheduled whenever an I/O operation completes. This requires limited superuser privileges.
• 1 to 63 (Except SGI)
  Increase the priority of the I/O threads by the value specified.
• +64 (Except SGI)
  Run the threads in system scope.
• +128 (Except SGI)
  Use SCHED_FIFO for scheduling. (Default is SCHED_OTHER).
• +256 (Except SGI)
  Use SCHED_RR for scheduling. (Default is SCHED_OTHER).
• +512 (Except SGI)
  Run threads DETACHED. (Default is JOINABLE).

This parameter is mostly used by Multipath in studying the scheduling policies on various platforms. On systems using pthreads, the default is to run the threads in process scope. The threads are scheduled as a group dynamically. The alternative is to run the threads in system scope, in which each threads is scheduled independently. Using system scope scheduling can be beneficial during development to study the behavior of each thread.

For good I/O performance, it is important to schedule the I/O threads as soon as there is work to do. Under most conditions, the default scheduling policy gives satisfactory performance. This Parameter provides for increasing the priority of the I/O threads over the compute threads to study the efficiency of the default scheduling policy.

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