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Technical Perspective: Measuring Optimization Potential with Coz

When programmers want to improve their program's performance, they often turn to profilers to tell them what code to optimize. A profiler can measure many aspects of a program's behavior, such as how many times each method is typically called, how long each method typically takes, and which methods typically lie on the critical path. Unfortunately, this information is not always relevant, and it can often cause programmers to waste their time on optimizations that have little impact on overall performance.

In particular, conventional profilers struggle to help developers optimize multithreaded programs. A simple but useful example is a program in which an initial thread waits for several worker threads to complete. If each worker runs for approximately the same amount of time, then most profilers will report that each worker accounted for an equal share of the execution time. At the same time, optimizing any individual worker will have a minimal impact on overall execution time since the program will only finish after all workers are done. A programmer could waste countless hours optimizing code without making the program run any faster.


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