The University of Georgia Department of Computer Science Department of Computer Science Introducing Parallelism through Sorting Integrating Concepts from Parallel and Distributed Computing into the Undergraduate Curriculum Eileen Kraemer

The University of Georgia Department of Computer Science Department of Computer Science Overview We are implementing an integrated approach to the inclusion of concepts in Parallel and Distributed Computing (PDC) in the undergraduate Computer Science curriculum. Timeline: – Spring ‘11 Intro to Computing and Programming (CSCI1301) – Fall ‘11 Software Development (CSCI 1302) – Spring’12 C++ and Unix Systems Programming (CSCI 1730) Data Structures (CSCI 2720)

The University of Georgia Department of Computer Science Department of Computer Science Intro to Computing & Programming Adaptation of this course involves the inclusion of several guest lectures, the first of which uses an evaluation of sorting algorithms to motivate and define parallelism and provide a platform for the discussion of the benefits and limitations of parallel processing. Thursday, April 21 st 3 sections ~100 students

The University of Georgia Department of Computer Science Department of Computer Science Introducing Parallelism Concepts: – definition and rationale of parallel and distributed computing – parallel sorting

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Students were first asked to complete a survey of their knowledge of parallelism, sorting, and time complexity concepts. – See appendix for questions and representative responses.

The University of Georgia Department of Computer Science Department of Computer Science Motivating the notion of cost Human Bubblesort – Roles: Processor – Directed the students to change places, according to algorithm Array elements – held up signs with their value (57,92,77,...) Comparison counter – Given a bag of 50 Tootsie rolls. Had to pay one per compare. Swap counter – Given a bag of 50 chocolate eggs. Had to pay one per swap. Step counter – Kept a tally of the number of operations.

The University of Georgia Department of Computer Science Department of Computer Science Time Complexity Analysis XXXXXXXX We keep track of the number of XXXXXXX comparisons & swaps & then XXXXXX use this sketch to convince XXXXX ourselves that Bubblesort XXXX is an n 2 algorithm. XXX XX X

The University of Georgia Department of Computer Science Department of Computer Science Human MergeSort Students again act out the process of sorting an array of 8 elements. Use Mergesort Time Complexity Analysis performed

The University of Georgia Department of Computer Science Department of Computer Science MergeSort: time complexity 1 - XXXXXXXX11 - XXXX 2 – XXXX 12 - XX 3 – XX 13 - X 4 – X 14 - X 5 - X 15 - XX 6 - XX 16 - XX 7 - X 17 - X 8 - X 18 - X 9 - XX 19 - XX 10 –XXXX 20 - XXXX 21 – XXXXXXXX... and we convince ourselves that Mergesort is n log n

The University of Georgia Department of Computer Science Department of Computer Science Observation: The “array elements” spend most of their time waiting around with nothing to do Idea: – use more processors!

The University of Georgia Department of Computer Science Department of Computer Science Human Parallel MergeSort

The University of Georgia Department of Computer Science Department of Computer Science Time complexity analysis & discussion faster in terms of time (steps) – but same number of comparisons – and there’s a limit to the benefit of add’l processors – and some processors participate only briefly sequential elements remain

The University of Georgia Department of Computer Science Department of Computer Science Conclusion What affects running time? – size of problem – choice of algorithm – use of parallelism nature of problem; percent sequential – code optimization – leveraging domain knowledge characteristics of input set (e.g., already ordered)

The University of Georgia Department of Computer Science Department of Computer Science Post-survey administered Currently under analysis

The University of Georgia Department of Computer Science Department of Computer Science Appendices

The University of Georgia Department of Computer Science Department of Computer Science Explanation... This lecture was presented on to 100 undergraduate CS students. Compilation and analysis of their responses is under way and will be included in this appendix. Results of analysis will be incorporated into the presentation.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses What does “parallel computing” mean?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses What are some of the benefits of parallel computing? That is, why might parallel computing be useful/helpful?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How are these benfits limited, if at all?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses What are some of the costs of parallel computing?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses Imagine that you have 8 test papers and that you want to put them into order by grade, from lowest to highest. The operations that you can use in performing the sort are: – to compare the values of two papers – to swap the locations of two papers in the collection You don’t have any information about the actual test grades or the initial ordering of the test papers.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How many comparisons might you have to perform, roughly?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How many swaps might you have to perform to sort the papers?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses Assume that each compare or swap takes one second, an any other work takes 0 time. How long might it take to sort the papers?

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses Now, imagine that you are asked to sort 1024 papers rather than 8. You can have some friends help you, but you have to pay them $5 to enter the room and $1 for each time step (time required for a compare or swap) during which they are present. Your goal is to minimize the time and the cost of performing the sort.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses Explain how you and your friends would share and coordinate the work of sorting the papers.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How quickly can you sort the papers now? Explain, briefly.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How many comparisons are required? Explain, briefly.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How many swaps are required? Explain, briefly.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses How many friends would you use? Explain, briefly.

The University of Georgia Department of Computer Science Department of Computer Science Pre-test Questions & Responses Name all the factors you can think of that might affect the running-time of a sorting program. Then, number the factors in order, using #1 for the factor that has the most effect and higher numbers for factors with lesser effects.