L8 - Computer Performance ECS 154B Computer Architecture II...

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1 ECS 154B Computer Architecture II Winter 2008 Computer Performance Chapter 4 2 Computer Performance • What is “performance?” – Method of comparison • Main computer performance metrics – Latency: How long to complete X? – Throughput: How many completed in Y? • Other metrics – Power – Energy – Cost – Scalability 3 Defining Performance • In performance, larger is better – Performance of 10 better than performance of 5 • What about latency? Smaller is better. • (Latency) Performance P = 1/T P: Performance T: Latency (execution time) 4 Comparing Performance • A is n times better than B n = P A /P B n: Improvement factor P A P B : Performance of A and B or n = T B /T A T B ,T A : Execution time of A and B
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2 5 Measuring Latency or Execution Time • Time required to execute a program • Function of – Instruction count – Clock frequency – Clock cycles per instruction • Performance Equation: T = CPI • I • P = CPI • I / f T: Time to execute the program I: Instruction count CPI: Clocks per instruction P: Clock period f: Clock frequency 6 Removing Noise • What factors affect the Latency? – Program (functionality, compiler) – CPU Design (clock cycle, CPI) – I/O Latency (hard drive or network access) – OS operations (process scheduling) • We want to remove aspects not associated with CPU design – Only consider time spent by CPU on the program
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This note was uploaded on 05/06/2008 for the course ECS 154b taught by Professor Krado during the Winter '08 term at UC Davis.

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L8 - Computer Performance ECS 154B Computer Architecture II...

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