Performance & Measuring

Question 1

Speedup

Answer 1

old time/new time
assuming old time is longer than new time

Question 2

Amdahl’s Law equation

Answer 2

speedup = 1/ ( (1 - f) + (f/s) )
f is the fraction of time spend in optimisable code
s is the speed up of the optimized code

Question 3

Amdahl’s Law in words

Answer 3

The maximum speedup of a program is limited by the fraction of the program that can not be improved.

Question 4

Properties to compare processors

Answer 4

the time in seconds to run a program/benchmark.
time = no. of instructions x CPI x cycle period

Question 5

Properties CANNOT used to compare processors

Answer 5

clock frequency, cycles per instructions, instruction per cycle,no. of floating point operations done per second.

Question 6

What information does gprof provide?

Answer 6

count and measures where time is spend.

how much time the program spends running a function. Gives insight to where time is spend.

Question 7

What information does gcov provide?

Answer 7

gives counts for each line of code. Decide which loops are most important and which if/else statements are most important to the program. Like the one ran most. Basically path most taken. Or the parts that really determine the logic of the program.

Question 8

How does gprof work?

Answer 8

Periodically interrupts program

Question 9

Observer Effect

Answer 9

when you want to observe how a program runs, you need to add code to it and change the way it is run.

effects: slows down execution time and size of program