Parallelism in Real-Time Applications

Parallelism in Real-Time Applications

In real-time programs such as aircraft or vehicle simulators, separate processes are used to distribute the work of the simulation onto multiple CPUs. In these demanding applications, the programmer frequently uses IRIX facilities to

reserve one or more CPUs of a multiprocessor for exclusive use by the application
isolate the reserved CPUs from all interrupts
assign specific processes to execute on specific, reserved CPUs

These facilities are described in detail in the REACT Real-Time Programmer's Guide (007-2499-00x). Also covered in that book is the use of the Frame Scheduler, an alternate process scheduler. The normal process scheduling algorithm of the IRIX kernel attempts to keep all CPUs busy and to keep all processes advancing in a fair manner. This algorithm is in conflict with the stringent needs of a real-time program, which needs to dedicate predictable amounts of hardware capacity to its processes, without regard to fairness.

The Frame Scheduler seizes one or more CPUs of a multiprocessor, isolates them, and executes a specified set of processes on each CPU in strict rotation. The Frame Scheduler has much lower overhead than the normal IRIX scheduler; and it has features designed for real-time work, including detection of overrun (when a scheduled process does not complete its work in the necessary time) and underrun (when a scheduled process fails to execute in its turn).

At this writing there are no real-time applications that use multiple nodes of an Array system.