Pipelining as a Computational Method

Pipelining as a Computational Method

• Before revising pipelining as a computational method, it is important to revise the concept of pipelining within the CPU first.

What is Pipelining?

• Pipelining is the process of carrying out multiple instructions concurrently
• It improves the overall efficiency and performance of a task or instruction
• In order to utilise pipelining it can be broken down into the following stages:
  1. Break down the task - analyse the process carefully to identify the individual tasks that make up the overall job
  2. Arrange in sequential order - organise the tasks into a logical sequence, where the output of one task becomes the input for the next
  3. Allow multiple tasks to operate at the same time - instead of waiting for one task to fully complete before starting the next one, allow multiple tasks to operate concurrently

Pipelining in Programming

• In languages such as Python and Java pipelining is chaining multiple instructions together
• Pipelining is a similar concept to an assembly line which is used to make the overall process more efficient
• Here is an example program written in Python that generates squared values of numbers from a list and then filters them to find only the even values

01 list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
02 squared = [x**2 for x in list]
03 filtered = [x for x in squared if x % 2 == 0]
04 print(filtered)

• Line 01 creates a list of ten numbers
• Line 02 uses iteration to square each value in the list one by one and generate a new list called ‘squared’
• Line 3 filters the new list, searching for each even number and adding them to a separate list called “filtered”
• On line 04 we print the filtered list, the final output would be:

[4, 16, 36, 64, 100]

• In the first example commands are separated by being on their own individual numbered lines, in other languages such as Unix the ’|’ symbol is used to separate commands
• Each command in the ‘pipeline’ is separated and data flows left to right
• An example of the ’|’ symbol used in Unix:

grep "hello" docs | grep "world"

• Here two grep commands (search) are chained together to perform a specific task
• The first grep command grep "hello" docs searches for lines that contain the word “hello” in a list of files contained in a file named ‘docs’
• The pipe symbol ’|’ connects the output of the first command to the input of the second command meaning only lines containing the word “hello” are passed to the second command
• The second grep command grep "world" searches for lines in the filtered results from command 1 that contain the word “world”

Worked Example

When a car is manufactured, the following activities take place:

• Designs drawn
• Engine developed
• Chassis developed
• Electronics planned
• Welding to create the body of the car
• Painting to protect the cars exterior
• Engine assembled
• Interior assembly
• Wheels attached
• Final inspection

Define the term ‘pipelining’ [2]

• Carrying out instructions concurrently [1]
• The result from one process/procedure feeds into the next [1]

Explain how the principles of pipelining can be applied to ensure a car is manufactured as quickly as possible [4]

• Identify tasks that can be carried out at the same time [1] for example, the engine and chassis can be developed separately but at the same time once the designs have been drawn [1]
• Identify tasks that must be completed in order [1] for example, painting once the body has been created/final inspection once all other tasks have been completed [1]

Describe one example of where pipelining is user in a computer system [2]

• Pipes to pass data between programs [1] for example, the | symbol used in Unix [1]