Book Image

OpenCL Programming by Example

Book Image

OpenCL Programming by Example

Overview of this book

Research in parallel programming has been a mainstream topic for a decade, and will continue to be so for many decades to come. Many parallel programming standards and frameworks exist, but only take into account one type of hardware architecture. Today computing platforms come with many heterogeneous devices. OpenCL provides royalty free standard to program heterogeneous hardware. This guide offers you a compact coverage of all the major topics of OpenCL programming. It explains optimization techniques and strategies in-depth, using illustrative examples and also provides case studies from diverse fields. Beginners and advanced application developers will find this book very useful. Beginning with the discussion of the OpenCL models, this book explores their architectural view, programming interfaces and primitives. It slowly demystifies the process of identifying the data and task parallelism in diverse algorithms. It presents examples from different domains to show how the problems within different domains can be solved more efficiently using OpenCL. You will learn about parallel sorting, histogram generation, JPEG compression, linear and parabolic regression and k-nearest neighborhood, a clustering algorithm in pattern recognition. Following on from this, optimization strategies are explained with matrix multiplication examples. You will also learn how to do an interoperation of OpenGL and OpenCL. "OpenCL Programming by Example" explains OpenCL in the simplest possible language, which beginners will find it easy to understand. Developers and programmers from different domains who want to achieve acceleration for their applications will find this book very useful.

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OpenCL Programming by Example
Dec, 2013 | 304 pages
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Table of Contents (18 chapters)
OpenCL Programming by Example
OpenCL Programming by Example
Credits
Credits
About the Authors
About the Authors
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
Hello OpenCL
Hello OpenCL
Advances in computer architecture
Different parallel programming techniques
Introduction to OpenCL
OpenCL components
An example of OpenCL program
Summary
References
2
OpenCL Architecture
OpenCL Architecture
Platform model
Platform versions
Execution model
Memory model
OpenCL ICD
Application scaling
Summary
3
OpenCL Buffer Objects
OpenCL Buffer Objects
Memory objects
Creating subbuffer objects
Histogram calculation
Reading and writing buffers
Copying buffers
Mapping buffer objects
Querying buffer objects
Undefined behavior of the cl_mem objects
Summary
4
OpenCL Images
OpenCL Images
Creating images
Samplers
Reading and writing buffers
Copying and filling images
Mapping image objects
Querying image objects
Image histogram computation
Summary
5
OpenCL Program and Kernel Objects
OpenCL Program and Kernel Objects
Creating program objects
Creating kernel objects
Summary
6
Events and Synchronization
Events and Synchronization
OpenCL events and monitoring these events
OpenCL event synchronization models
Coarse-grained synchronization
Event-based or fine-grained synchronization
Getting information about cl_event
User-created events
Event profiling
Memory fences
Summary
7
OpenCL C Programming
OpenCL C Programming
Built-in data types
Aliasing rules
Conversions and type casts
Operators
Address space qualifiers
Image access qualifiers
Storage class specifiers
Built-in functions
Summary
8
Basic Optimization Techniques with Case Studies
Basic Optimization Techniques with Case Studies
Finding the performance of your program?
Case study – matrix multiplication
Case study – Histogram calculation
Finding the scope of the use of OpenCL
General tips
Summary
9
Image Processing and OpenCL
Image Processing and OpenCL
Image representation
Implementing image filters
OpenCL implementation of filters
JPEG compression
Summary
References
10
OpenCL-OpenGL Interoperation
OpenCL-OpenGL Interoperation
Introduction to OpenGL
Defining Interoperation
Implementing Interoperation
Summary
11
Case studies – Regressions, Sort, and KNN
Case studies – Regressions, Sort, and KNN
Regression with least square curve fitting
Bitonic sort
k-Nearest Neighborhood (k-NN) algorithm
Summary
Index
Index

OpenCL components

Before delving into the programming aspects in OpenCL, we will take a look at the different components in an OpenCL framework. The first thing is the OpenCL specification. The OpenCL specification describes the OpenCL programming architecture details, and a set of APIs to perform specific tasks, which are all required by an application developer. This specification is provided by the Khronos OpenCL consortium. Besides this, Khronos also provides OpenCL header files. They are cl.h, cl_gl.h, cl_platform.h, and so on.

An application programmer uses these header files to develop his application and the host compiler links with the OpenCL.lib library on Windows. This library contains the entry points for the runtime DLL OpenCL.dll. On Linux the application program is linked dynamically with the libOpenCL.so shared library. The source code for the OpenCL.lib file is also provided by Khronos. The different OpenCL vendors shall redistribute this OpenCL.lib file and package it along with their OpenCL development SDK. Now the application is ready to be deployed on different platforms.

The different components in OpenCL are shown in the following figure:

Different components in OpenCL

On Windows, at runtime the application first loads the OpenCL.dll dynamic link library which in turn, based on the platform selected, loads the appropriate OpenCL runtime driver by reading the Windows registry entry for the selected platform (either of amdocl.dll or any other vendor OpenCL runtimes). On Linux, at runtime the application loads the libOpenCL.so shared library, which in turn reads the file /etc/OpenCL/vendors/*.icd and loads the library for the selected platform. There may be multiple runtime drivers installed, but it is the responsibility of the application developers to choose one of them, or if there are multiple devices in the platforms, he may want to choose all the available platforms. During runtime calls to OpenCL, functions queue parallel tasks on OpenCL capable devices. We will discuss more on OpenCL Runtimes in Chapter 5, OpenCL Program and Kernel Objects.

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