Computer for Low Contest-Switch Time

摘要

A context switch is the suspension of one running process and the activation ofanother in a multitasking environment. Many applications, such as process control, require frequent context switches among many processes. A context switch requires a substantial amount of time: about 1000 microseconds on a VAX 11/780 and about 500 microseconds on Sun 4/280. Recently introduced computer architectures, such as the Sun 4, have not improved context-switch performance as much as they have improved throughput. A computer architecture with appropriate memory hierarchy can give better support to context switching. The Computer for Low Context-Switch Time (CLOCS) is a computer with such an architecture. Because the architecture has minimum state inside the Central Processing Unit, CLOCS can switch context in less than the time required to execute one instruction. The CLOCS Memory Management Unit provides virtual memory without degrading context-switch time as long as the new process is located in physical memory. Analyses of the architecture show that CLOCS throughput performance approaches the performance of contemporary RISC workstations and that it is well suited for real-time applications. (KR)