cache optimization and performance evaluation of a structured cfd code

137 Pages·2016·1.19 MB·English

by  Anand B. Palki

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Anand B. Palki
University of Kentucky, [email protected]
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Palki, Anand B., "CACHE OPTIMIZATION AND PERFORMANCE EVALUATION OF A STRUCTURED CFD
CODE - GHOST" (2006). University of Kentucky Master's Theses. 363.
https://uknowledge.uky.edu/gradschool_theses/363
This Thesis is brought to you for free and open access by the Graduate School at UKnowledge. It has been
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ABSTRACT OF THESIS

CACHE OPTIMIZATION AND PERFORMANCE EVALUATION OF A STRUCTURED
CFD CODE - GHOST

This research focuses on evaluating and enhancing the performance of an in-house, structured,
2D CFD code - GHOST, on modern commodity clusters. The basic philosophy of this work is to
optimize the cache performance of the code by splitting up the grid into smaller blocks and
carrying out the required calculations on these smaller blocks. This in turn leads to enhanced
code performance on commodity clusters. Accordingly, this work presents a discussion along
with a detailed description of two techniques: external and internal blocking, for data access
optimization. These techniques have been tested on steady, unsteady, laminar, and turbulent test
cases and the results are presented. The critical hardware parameters which influenced the code
performance were identified. A detailed study investigating the effect of these parameters on the
code performance was conducted and the results are presented. The modified version of the code
was also ported to the current state-of-art architectures with successful results.

KEYWORDS: Cache Optimization, External blocking, Internal blocking, Structured CFD
Code Optimization, Commodity Clusters

Anand .B. Palki

12/15/2006

Copyright © Anand B Palki, 2006
CACHE OPTIMIZATION AND PERFORMANCE EVALUATION OF A STRUCTURED
CFD CODE - GHOST

By

Anand .B. Palki

Dr. Raymond .P. LeBeau
Director of Thesis

Dr. L. S. Stephens
Director of Graduate Studies

12/15/2005
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Name Date
THESIS

Anand B Palki

The Graduate School

University of Kentucky

2006
CACHE OPTIMIZATION AND PERFORMANCE EVALUATION OF A STRUCTURED
CFD CODE - GHOST

THESIS

A thesis submitted in partial fulfillment of the

requirements for the degree of Master of Science in Mechanical Engineering

in the College of Engineering at the University of Kentucky

By

Anand .B. Palki
Lexington, Kentucky

Director: Dr. Raymond .P. LeBeau

Assistant Professor of Mechanical Engineering
University of Kentucky Lexington, Kentucky
2006
To My Parents
ACKNOWLEDGEMENTS

The satisfaction and euphoria that accompany the successful completion of any task would
not be complete without the mention of the people who made it possible, whose constant
encouragement and guidance crowned the effort with success.
I would like to express my sincere gratitude to my academic advisor Dr. Raymond
LeBeau, for his continuous support and encouragement throughout my work. The progress of
this work would not be achieved without his guidance and numerous ingenious suggestions. I
would like to thank Dr. P.G. Huang for helping me understand how a CFD code works. I
would also like to thank my defense committee members Dr. Jamey Jacob and Dr. M. Seigler
for their valuable time for serving on my committee and evaluating my work.
I am grateful to my student collaegues who made my stay at the University of Kentucky
a memorable one. I am especially grateful to Abhishek T, Ajay Babu, Aditya C, Chaitanya
Penugonda, Chetan Babu, Daniel R, Jacky Rhinehart, Karthik M, Narendra BK, Phanindra C,
Radhika K, Sandeep B, Snehal P and Vijay N for their emotional support, entertainment,
caring and most importantly for being the surrogate family over the past two years. Finally, I
would like to thank my parents for their continuous encouragement and love without which
none of this would have been possible.

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Table of Contents

Acknowledgements............................................................................................................................................vii
List of Tables.....................................................................................................................................................x
List of Figures...................................................................................................................................................xi
List of Files.....................................................................................................................................................xiii
1. Introduction......................................................................................................................................................1
1.1 Overview.................................................................................................................................................1
1.2 Background - Memory Hierarchy...........................................................................................................2
1.3 Introduction to Problem..........................................................................................................................6
1.4 Goals of Optimizing the Code................................................................................................................7
1.5 Previous Work........................................................................................................................................8
1.5.1 General Cache Optimization Techniques........................................................................................8
1.5.1.1 Techniques for Reducing Capacity Misses..............................................................................9
1.5.1.2 Techniques for Reducing Conflict Misses.............................................................................11
1.5.1.3 Techniques to Hide Effects of Cache Misses........................................................................12
1.5.1.4 Techniques to Improve the Replacement Decisions by Cache..............................................13
1.5.2 Optimizations to CFD Codes........................................................................................................13
1.5.2.1 Techniques to Improve Parallel Performance:.......................................................................13
1.5.2.2 Techniques to Improve Single Node Performance:...............................................................14
1.6 External & Internal Blocking................................................................................................................15
2. Computational tools.......................................................................................................................................17
2.1 General Description of GHOST............................................................................................................17
2.1.1 GHOST Flowchart........................................................................................................................18
2.1.2 Governing equations.....................................................................................................................19
2.1.3 Calculation at artificial boundaries................................................................................................21
2.2 Grid File Data.......................................................................................................................................22
2.2.1 Finite Volume Method..................................................................................................................22
2.2.2 Generalized coordinates................................................................................................................22
2.2.3 Description of G.F90 Output.........................................................................................................25
2.2.4 Description of Input File...............................................................................................................26
2.3 Compilers & MPI Environment............................................................................................................26
2.4 Valgrind [79].........................................................................................................................................28
2.5 Kentucky Fluid Clusters........................................................................................................................30
2.6 Method used to measure performance..................................................................................................31
2.7 Summary...............................................................................................................................................32
3. External Blocking Results..............................................................................................................................33
3.1 Terminology..........................................................................................................................................33
3.1.1 Terms related to Code Versions....................................................................................................33
3.1.2 Terms related to performance study test results description.........................................................34
3.1.3 Terms related to cache behavior study test results........................................................................34
3.2 Test Case...............................................................................................................................................35
3.3 Types of Tests.......................................................................................................................................35
3.4 External Blocking.................................................................................................................................37
3.5 Performance Test Results......................................................................................................................37
3.5.1 KFC4 Results................................................................................................................................37
3.5.2 KFC5 Results................................................................................................................................41
3.5.3 Rectangular Blocks.......................................................................................................................42
3.5.4 Effects of Compiler Optimization Levels on Performance...........................................................43

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3.5.5 Effects of Different Compilers on Performance............................................................................46
3.5.5 Effect of different hardware on performance................................................................................50
3.5.6 Steady Turbulent Case Performance Results................................................................................53
3.6 Valgrind Results....................................................................................................................................57
3.6.1 KFC4 Results................................................................................................................................57
3.6.2 Comparison between G95 & IFC..................................................................................................59
3.6.3 Effect of Cache Thrashing.............................................................................................................62
3.6.4 Valgrind Results for Turbulent Case.............................................................................................63
3.7 Accuracy Test Results...........................................................................................................................64
3.8 Summary...............................................................................................................................................67
4. Internal Blocking Results...............................................................................................................................68
4.1 Basic Principle......................................................................................................................................68
4.2 Implementation of Internal Blocking in GHOST..................................................................................68
4.3 Primary Tests........................................................................................................................................71
4.4 Performance Test Results......................................................................................................................72
4.4.1 Comparison of Performance Test Results between External and Internal Blocking.....................74
4.5 Valgrind Results....................................................................................................................................76
4.5.1 Comparison of Valgrind results between Internal and External Blocking....................................79
4.6 Accuracy Test Results...........................................................................................................................81
4.7 Summary...............................................................................................................................................84
5. Unsteady Test Case Results...........................................................................................................................85
5.1 Laminar Unsteady Test Case................................................................................................................85
5.2 Performance Test Results......................................................................................................................87
5.3 Accuracy Test Results...........................................................................................................................90
5.4 Summary...............................................................................................................................................93
6. Conclusions And Future Work.....................................................................................................................94
6.1 Summary and Conclusions....................................................................................................................94
6.2 Future Work..........................................................................................................................................98
Appendix...........................................................................................................................................................100
A.1 Steps to implement internal blocking to GHOST...............................................................................100
References.........................................................................................................................................................116
Vita................................................................................................................................................................122

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