By providing complete,control over process priority as well as the assignment of processes and
interrupts to processors, IRIX enables simplified system software implementations, minimal
latency, and maximal CPU utilization.
4.4.1 Deterministic Response
Unix was originally designed to distribute CPU time and other system resources equally4.4.2 Interruptible Kernel
among users,of a time-sharing system. As a result, predicting precisely when any event will
occur in a generic Unix system is-impossible. IRIX with REACT includes the following
extensions to generic Unix which, together, result in a fully deterministic system that is
suitable for real-time applications.
When running in kernel mode, IRIX periodically allows user-level interrupts to be processed.4.4.3 Precise Process Priority Control
Users can assign a process to one of three priority bands: above, equal to, or below normal4.4.4 Non-Degrading Priority
Unix processes. Within each band, processes can be assigned one of at least 32 vertical priority
Users can also prevent the Unix scheduler's aging mechanism from decreasing the priority of a4.4.5 Locking Memory Pages
process as its run time accumulates. This freezes the process' priority at the assigned level.
A process can be locked into mehiory, ensuring that it will never be swapped out onto disk.4.4.6 Processor Isolation
On a multiprocessor system, a subset of the processors can be isolated from the non-
determinism introduced by disk and network I/O processing.
POWER Lock(tm) Processor Isolation, a feature of IRIX Release 4.0, goes beyond isolating a
processor from non-determinism to allow a user to isolate a processor from certain memory
management activities that extend interrupt latency.
Communication among processors via shared memory is not affected by processor isolation.
Processes running on isolated processors have full access to all Unix services.
No system is an island, so SkyWriter supports a variety of options for I/O to secondary storage
devices, networks, and third party devices.