Lecture_9 - ECE 445 Computer Organization Performance...

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ECE 445 – Computer Organization Performance (Lecture #9)
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ECE 445 - Computer Organization 2 How is performance evaluated? What makes one system “better” than another? What metrics are used to characterize performance?
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ECE 445 - Computer Organization 3 Measuring Performance Response Time – the time between the start and completion of a task - Also called Execution Time Throughput – the total amount of work done in a given period of time There are different performance metrics , based on the measurement of interest, to characterize and compare system performance.
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ECE 445 - Computer Organization 4 Performance How are response time and throughput affected by 1. The use of a faster processor? 2. The use of multiple processors?
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ECE 445 - Computer Organization 5 Performance 1. The use of a faster processor results in shorter response time and greater throughput.
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ECE 445 - Computer Organization 6 Performance 2. The use of multiple processors results in greater throughput but no change in response time.
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ECE 445 - Computer Organization 7 Performance and Execution Time To maximize performance, we want to minimize response time (or execution time) for each task. Performance X = 1 Execution Time X where Performance X is the performance of computer X and Execution Time X is the execution time of computer X.
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ECE 445 - Computer Organization 8 Performance and Execution Time When comparing two computers, Computer X and Computer Y: If Performance X > Performance Y then Execution Time X < Execution Time Y
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ECE 445 - Computer Organization 9 Performance and Execution Time If Computer X is n times faster than Computer Y then n = Performance Y Performance X Execution Time X Execution Time Y =
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ECE 445 - Computer Organization 10 Example: Relative Performance
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ECE 445 - Computer Organization 11 Time required to execute a program: Computer X requires 10 seconds Computer Y requires 15 seconds n = Performance Y Performance X Execution Time X Execution Time Y = n = 10 seconds 15 seconds = 1.5 Computer X is 1.5 times faster than computer Y
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ECE 445 - Computer Organization 12 Measuring Execution Time Elapsed Time - Total response time of the system Includes processing, I/O, OS overhead, idle time - Determines system performance CPU Time (aka. CPU Execution Time) - Time spent processing a given task Does not include I/O time Does not include time spent processing other tasks (i.e. multi-tasking).
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ECE 445 - Computer Organization 13 CPU Clocking Operation of digital hardware governed by a constant- rate clock Clock (cycles) Data transfer and computation Update state Clock period Clock period: duration of a clock cycle e.g., 250ps = 0.25ns = 250×10 –12 s Clock frequency (rate): cycles per second e.g., 4.0GHz = 4000MHz = 4.0×10 9 Hz
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ECE 445 - Computer Organization 14 CPU Time Performance improved by - Reducing number of clock cycles - Increasing clock rate - Hardware designer must often trade off clock rate against cycle count Rate Clock Cycles Clock CPU Time Cycle Clock Cycles Clock CPU Time CPU = × =
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ECE 445 - Computer Organization 15 Example: Calculation using the CPU Time
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Lecture_9 - ECE 445 Computer Organization Performance...

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