7 - Performance (1).pptx

7 - Performance (1).pptx - PERFORMANCE Introduction The...

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PERFORMANCE

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Introduction The performance of a system depends on: algorithms programming language architecture hardware elements Assessing performance can be challenging
Introduction What is performance? Airplane Passengers Range Speed Throughput Boeing 747 470 4150 610 286,700 Concorde 132 4000 1350 178,200 DC-8-50 146 8720 544 79.424

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Definitions of Performance Response time How long it takes to do a task Execution time Throughput Total work done per unit time e.g., tasks/transactions/… per hour
Performance as Response Time To increase performance, reduce response time. “X is n time faster than Y” Performance(X) Execution Time(Y) –––––––––––––– = –––––––––––––––– = n Performance(Y) Execution Time(X) 1 Performance(X) = –––––––––––––––– Execution Time(X)

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Example If computer A runs a program in 10 seconds and computer B runs the same program in 15 seconds, how much faster is A than B? A is 1.5 times faster than B. Execution Time(B) 15 –––––––––––––– = –––––––––––––––– = n Execution Time(A) 10 Execution Time(B) 15 –––––––––––––– = –––––––––––––––– = 1.5 Execution Time(A) 10 Performance(A) Execution Time(B) –––––––––––––– = –––––––––––––––– = n Performance(B) Execution Time(A)
Measuring Performance Time is our metric for determining performance Time can be defined in different ways

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Measuring Execution Time Elapsed time Wall-clock” time, Response time Total time to complete task, including all aspects Processing, I/O, OS overhead, idle time Determines system performance CPU time Time spent processing a given job Discounts I/O time, other jobs’ shares Comprises user CPU time and system CPU time Different programs are affected differently by CPU and system performance CPU Performance System Performance
CPU Clocking Clock period: duration of a clock cycle e.g. 250 ps Clock frequency: cycles per second e.g. 4 GHz Clock (cycles) Data transfer and computation Update state Clock period

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CPU Time Performance improved by Reducing number of clock cycles Increasing clock rate Trade-offs: Designers often trade off clock rate against cycle count CPU Time = CPU Clock Cycles x Clock Cycle Time
Example Our favorite program runs in 10 seconds on computer A, which has a 4 GHz clock . We are trying to help a computer designer build a computer, B, that will run this program in 6 seconds. The designer has determined that a substantial increase in the clock rate is possible , but this increase will affect the rest of the CPU design, causing computer B to require 1.2 times as many clock cycles as computer A for this program.

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