Scheduling and System Performance

The scheduler determines when and for how long processes run. Therefore, the behavior of the scheduler strongly affects system performance.

By default, all user processes are time-sharing processes. A process changes class only by a priocntl() call.

All real-time process priorities have a higher priority than any time-sharing process. Time-sharing processes or system processes cannot run while any real-time process is runnable. A real-time application that occasionally fails to relinquish control of the CPU can completely lock out other users and essential kernel housekeeping.

Besides controlling process class and priorities, a real-time application must also control other factors that affect its performance. The most important factors in performance are CPU power, amount of primary memory, and I/O throughput. These factors interact in complex ways. The sar command has options for reporting on all performance factors. For information about sar command, see the sar(1) man page and for information about priocntl() call, see the priocntl(2) man page.