A system with two dual-core processors has four processors available for schedul

Question

A system with two dual-core processors has four processors available for scheduling. A CPU-intensive application is running on this system. All input is performed at program start-up, when a single file must be opened. Similarly, all output is performed just before the program terminates, when the program results must be written to a single file. Between startup and termination, the program is entirely CPU-bound. Your task is to improve the performance of this application by multithreading it. The application runs on a system that uses the one-to-one threading model (each user thread maps to a kernel thread). middot How many threads will you create to perform the input and output? Explain. middot How many threads will you create for the CPU-intensive portion of the application? Explain.

Explanation / Answer

• It only makes sense to create as many threads as there are blocking system calls, as the thread will be spent blocking. Creating additional threads provides no benefit. Thus, it makes sense to create a single thread for input and a single thread for output.

• Four threads needed for the CPU-intensive portion of the application. There should be as many threads as there are processing cores. Fewer would be a waste of processing resources, and any number >   4 would be unable to run.

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