Performance of the Architecture

Question 1

What does the fundamental concept in computer architecture state

Answer 1

programs tend to access a small, localised portion of memory repeatedly over short periods of time

Question 2

What’re the two mains types of locality

Answer 2

Temporal Locality (locality in time)
Spatial Locality (locality in space)

Question 3

Define temporal locality

Answer 3

If a memory location is accessed, it is likely to be accessed again soon

Question 4

Define spatial locality

Answer 4

if a memory location is accessed, nearby location are also likely to be accessed soon

Question 5

Describe temporal locality using a real-world analogy

Answer 5

if you use a book frequently, you keep it on your desk rather than returning it to the shelf every time

Question 6

Describe spatial locality using a real-world analogy

Answer 6

if you pick up a book from a shelf, you’re likely to pick other books from the same section

Question 7

Give an example of temporal locality

Answer 7

A loop iterating over an array repeatedly accesses the same variable multiple times

Question 8

Give an example of spatial locality

Answer 8

When accessing an element of an array, adjacent elements are often accessed next (as in sequential loops)

Question 9

What is the 90-10 rule of thumb

Answer 9

States that programs spend 90% of their execution time in just 10% of the code

Question 10

What are the key takeaways from the 90-10 rule

Answer 10

• Focus on optimising the critical 10% of code rather than the premature optimisation of the entire program
• recognise demising returns
• favour the common case

Question 11

Define Amdahl’s Law

Answer 11

States that the performance improvements to be gained from using some faster mode of execution (or parallelism) is limited by the fraction of timetnat faster mode can be used

Question 12

What is the speed up equation

Answer 12

performance for entire task using enhancement when possible
Speedup = ——————————————————————————————–
Performance for entire task without using enhancement

                execution time for entire task without using enhancement Speedup = --------------------------------------------------------------------------------------------
                 Execution time for entire task using the enhancement when possible

Question 13

Overall what two parts is speed up comprised off

Answer 13

1 - The fraction of computation time in the original computer that can be converted to take advantage of the enhancement

2 - The improvement gained by the enhancement execution mode, i.e., how much faster the task would run if the enchanced mode were used for the entire program (the time of the original mode over the time of the enchanted mode)

Question 14

What is the overall speed up equation

Answer 14

execution time (new)

Question 15

Example for over all speed up:

Answer 15

(1 - fraction(enhanced) + Fraction(enhanced)
—————————-
Speedup(enhanced)

Question 16

Define block

Answer 16

the minimum unit of information that can either present or not present in the memory hierarchy

Question 16

Define Hit rate

Answer 16

the fraction of memory accesses found in cache

Question 17

Define miss rate

Answer 17

the fraction of memory accesses not found in a certain level of memory (1 - hit rate)

Question 18

Define hit time

Answer 18

time required to access a level of memory hierarchy when it is a hit

Question 19

Define miss penalty

Answer 19

time required to replace a clock of memory in upper level with a lock from lower level plus the time to deliver the block to processor