Computers as Components, 2nd Edition

368 CHAPTER 7 Multiprocessors

7.3.3 Buffering and Performance

Moving data in a multiprocessor can incur significant and sometimes unpredictable

costs. When we move data in a uniprocessor, we are copying from one part of

memory to another, we are doing so within the same memory system. When we

move data in a multiprocessor,we may exercise several different parts of the system,

and we have to be careful to understand the costs of those transfers.

Consider, as an example, copying an array. If the source and destination are

in different memories, then the data transfer rate will be limited by the slowest

element along the path: the source memory, the bus, ...