多核程序设计之三分析报告.ppt

* * * * * * * * * * * * * Multi-core Programming: Basic Concepts Speaker’s Notes [Purpose of this Slide] Show how speedup is computed in fence painting example for various numbers of painters. [Details] The fence graphic along the right edge will be automatically put in after 5 seconds. Infinite painters is the theoretical maximum and means that the time to paint the fence can be as close to zero as desired. Build shows box relating discussion to Amdahl’s law. The use of a spray gun introduces a better serial algorithm. Future speedup calculations must then use this serial algorithm timing (since no one would go back to an inferior serial algorithm when given the chance to use something better). The new serial time with the spray gun is then 120 minutes (30 + 60 + 30) with the same serial setup and cleanup time. The assumption in the example is that the spray gun cannot be used if there are more than one painter, thus, there is no advantage from the spray gun in the parallel case. The theoretical maximum speed up, in light of the spray gun, is 2.0X with an infinite number of painters (120 / 60 = 2.0). * Multi-core Programming: Basic Concepts Speaker’s Notes [Purpose of this Slide] Define and show how to compute the Efficiency metric for parallel processors (threads). [Details] Efficiency is a measure of how busy the threads are during parallel computations. Low efficiency numbers may prompt the user to run the application on fewer threads/processors and free up resources to run something else (another threaded process, other user’s codes). Build transforms some potential workers into lay-abouts enjoying not having to do much work, but still getting paid for the whole time that the job is being conducted (all the serial time for set up and cleaning). * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 锁的粒度 锁的粒度 锁的粒度是上锁后保护的共享数据的多少，当一个线程加锁并访问这些数据期间，其它线程无法访问。 减小锁的粒度可以提高对共享数据访问的并行性，可以更加充分利用并行处理能力。例如：对树的访问 * 锁的粒度 * 锁的粒度和死锁 死锁 两个线程分别拥有锁，并等待