ele74904performance - Lecture 04: Understanding Performance...

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ELE749 L04 Understanding Performance.1 Lecture 04: Understanding Performance Ali Ziya Alkar ELE 749 Computer Organization and Design [Adapted from Computer Organization and Design , Patterson & Hennessy, © 2005, UCB]
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ELE749 L04 Understanding Performance.2 Indeed, the cost-performance ratio of the product will depend most heavily on the implementer, just as ease of use depends most heavily on the architect. The Mythical Man-Month , Brooks, pg 46
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ELE749 L04 Understanding Performance.3 Performance Metrics ± Purchasing perspective z given a collection of machines, which has the - best performance ? - least cost ? - best cost/performance? ± Design perspective z faced with design options, which has the - best performance improvement ? - least cost ? - best cost/performance? ± Both require z basis for comparison z metric for evaluation ± Our goal is to understand what factors in the architecture contribute to overall system performance and the relative importance (and cost) of these factors
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ELE749 L04 Understanding Performance.4 Defining (Speed) Performance ± Normally interested in reducing z Response time (aka execution time) – the time between the start and the completion of a task - Important to individual users z Thus, to maximize performance, need to minimize execution time performance X = 1 / execution_time X If X is n times faster than Y, then z Throughput – the total amount of work done in a given time - Important to data center managers z Decreasing response time almost always improves throughput performance X execution_time Y -------------------- = --------------------- = n performance Y execution_time X
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ELE749 L04 Understanding Performance.5 Performance Factors ± Want to distinguish elapsed time and the time spent on our task ± CPU execution time (CPU time) – time the CPU spends working on a task z Does not include time waiting for I/O or running other programs CPU execution time # CPU clock cycles for a program for a program = x clock cycle time or CPU execution time # CPU clock cycles for a program for a program clock rate = ------------------------------------------- ± Can improve performance by reducing either the length of the clock cycle or the number of clock cycles required for a program
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ELE749 L04 Understanding Performance.6
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ele74904performance - Lecture 04: Understanding Performance...

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