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.
Table of Contents (18 chapters)
OpenCL Programming by Example
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
Index

Mapping buffer objects


OpenCL provides a mechanism to map a region of a buffer directly into host memory instead of using the clEnqueue[Read|Write]Buffer functions. These mapped regions can be returned to the application. The application can use this mapped memory region based on the cl_map_flags flag value which is set during mapping. Now the first question which would arise in the readers mind is that how different are the two APIs clEnqueueMapBuffer and clEnqueueReadBuffer.

The clEnqueueReadBuffer function reads into a memory location pre-allocated. But clEnqueueMapBuffer returns a pointer to the mapped region.

Other difference between clEnqueueReadBuffer and clEnqueueMapBuffer is the map_flags argument. If map_flags is set to CL_MAP_READ, the mapped memory will be read only, and if it is set as CL_MAP_WRITE the mapped memory will be write only, if you want both read and write, then set the flags as CL_MAP_READ|CL_MAP_WRITE. The importance of CL_MAP_READ lies when an unmap is called on...