High-Performance Embedded Computing

6.3 Real-Time Multiprocessor Operating Systems 339

Scheduling a multiprocessor is substantially more difficult than scheduling a

uniprocessor. Optimum scheduling algorithms do not exist for most realistic

multiprocessor configurations, so heuristics must be used. Equally important,

the information that one processor needs to make good scheduling decisions

often resides far away on another processor.

Part of the reason that multiprocessor scheduling is hard is that communica-

tion is no longer free. Even direct signaling on a wire can take several clock

cycles and the memory system may take tens of clock cycles to respond to a

request for a location in ...