Tuning CPU resources

Multiprocessor systems

The SCO OpenServer system is a multitasking, multiuser operating system, designed to share resources on a computer with a single CPU. It can run on a more powerful multiprocessor system but it cannot use more than one of the available CPUs.

SCO SMP License software adds multiprocessing-specific components to the standard operating system kernel, enabling it to recognize and use additional processors automatically. As SMP is implemented as an extension to, and is completely compatible with the version of the kernel that supports a single CPU. With SCO SMP License software installed, the operating system retains its multitasking, multiuser functionality. There is no impact on existing utilities, system administration, or filesystems. SMP can execute standard OMF (x.out), COFF, and ELF binaries without modification.

SMP is modular. As your system requires more processing power, you can add additional processors. For example, two processors give you twice the processing power of a single processor of identical specification in terms of the number of instructions per second that they can execute.

If the operating system can gain extra performance in direct proportion to the number of processors, it is said to exhibit perfect scaling as shown in ``Perfect multiprocessor scaling''. In practice, the processors have to compete for other resources such as memory and disk, they have to co-operate in how they handle interrupts from peripherals and from other CPUs, and they may have to wait to gain access to data structures and devices.

Perfect multiprocessor scaling

To ensure good scaling, you should ensure that the memory and I/O subsystems (particularly hard disks) are powerful enough to satisfy the demands that multiple processors put on them. If you do not match the power of your subsystems to that of the processors, your system is likely to be memory or I/O bound, and it will not utilize the potential performance of the processors.

A system will scale well when there are many ready-to-run processes. Multithreaded applications are also well suited to take advantage of a multiprocessing environment.

Next topic: Support for multiple processors
Previous topic: Examining the run queue

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003