Книга: Distributed operating systems

6.4.1. Basic Design

6.4.1. Basic Design

The idea behind DSM is simple: try to emulate the cache of a multiprocessor using the MMU and operating system software. In a DSM system, the address space is divided up into chunks, with the chunks being spread over all the processors in the system. When a processor references an address that is not local, a trap occurs, and the DSM software fetches the chunk containing the address and restarts the faulting instruction, which now completes successfully. This concept is illustrated in Fig. 6-25(a) for an address space with 16 chunks and four processors, each capable of holding four chunks.

In this example, if processor 1 references instructions or data in chunks 0, 2, 5, or 9, the references are done locally. References to other chunks cause traps. For example, a reference to an address in chunk 10 will cause a trap to the DSM software, which then moves chunk 10 from machine 2 to machine 1, as shown in Fig. 6-25(b).

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