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Symmetric versus Asymmetric Shared-Memory Multiprocessors
In an asymmetric,shared-memory MP,processors are not equal.One processor is designed as the master processor,and the others are slave processors.The master processor is a general-purpose processor which can perform I/O operations as well as computation while running the operating system.Slave processors can only perform computation.On a slave processor,all I/O operations and general kernel requests are routed to the master processor.Utilization of the slave processor might be poor if the master processor does not service slave processor requests efficiently.As an example,I/O-bound jobs may not run efficiently since only the master CPU runs the I/O operations.
In a symmetric shared-memory multiprocessor(SMP),all of the processors are functionally equivalent;they all can perform kernel,I/O and computational operations.The operating system manages a pool of identical processors,any one of which may be used to control any I/O devices or refer to any storage unit.Since all processors are equal,the system can be reconfigured in the event of a processor failure and,following reboot continue to run.Performance can be optimized,and more processors can be used.
对称与非对称共享内存多处理器
在非对称共享内存的多处理器中,各处理器地位不同,一个处理器设计成主处理器,其他则是从处理器。主处理器是一个通用处理器,它在运行操作系统的同时,能实现I/O操作以及计算工作。从处理器只能完成计算工作。对于从处理器,所有的I/O操作和一般的内核请求都转送给主处理器。如果主处理器未能有效地满足从处理器的请求,那么从处理器的利用率就会很低。例如,由于只有主CPU运行I/O操作,受I/O限制的作业运行很可能是低效的。
在对称共享内存多处理器(SMP)中,所有的处理器在功能上是等效的,它们都能完成内核、I/O和计算操作。操作系统管理同一个处理器池,每一个处理器都可以控制任何I/O设备或访问任何存储部件。因为所有的处理器都是一样的,系统可以在一个处理器发生故障时重新进行配置,接着重新引导,继续运行;可以优化性能,并使用更多的处理器。 |
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