nazpyro / swan

A simple tool for porting CUDA to OpenCL

SWAN Version 0.1 12 Mar 2010 (c) M J Harvey, Imperial College London [email protected]

INTRODUCTION

Swan is a simple tool for aiding a port from CUDA to OpenCL. It has the following benefits:

• Reduce reliance on nvcc for CUDA code by replacing the CUDA runtime extensions
• Automatic code generation of entry point functions for kernels, to replace <<<>>> syntax
• Source translation of CUDA kernels to OpenCL.
• Common API for both CUDA and OpenCL targets.

BUILDING

• In the top level directory (tld), edit config.mk and set the paths appropriately OpenCL and CUDA libraries may be selectively enabled with "OPENCL=yes|no" and "CUDA=yes|no"

• Set LD_LIBRARY_PATH to point to libOpenCL and other libs.

• Set PATH to point to (tld)/bin

• To build library and examples: $ cd (tld) $ make

  If all went well, you will have lib/libswan_(cuda|ocl).(so|a) and CUDA and/or OpenCL versions of each example (.nv and .ocl suffices)

• Build just the examples (having already built the library): $ cd (tld) $ make examples

EXAMPLES

Each example will build in OpenCL and CUDA variants, with suffices .ocl and .nv respectively.

• examples/vecadd A simple vector addition

• examples/vecadd_global A simple vector addition showing use of device/constant global data

• examples/shmem Shows use of dynamic shared memory

• examples/interp 1D Texturing, with arrays and linear memory (CUDA only)

PORTING EXISTING CUDA CODE

How to use in your own code:

• Put the kernels in a separate file, e.g. kernel.cu

• Include the compiled code in the host source: #include "kernel.kh"

• Replace CUDA-style kernel launches with calls to the entry point functions. The formal definitions of these functions are sytematically derived from the kernel source. For example, a kernel:

  global void func1( float4 *in, int *out, int N );

  will have the following entry points:

  void k_func1( block_config_t grid, block_config_t block, int shmem, float4 *in, int *out, int N );

  and

  void k_func1_async( block_config_t grid, block_config_t block, int shmem, float4 *in, int *out, int N );

  grid, block and shmem have the same definitions as in the CUDA launch syntax <<< grid, block, shmem >>>. block_config_t has 3 elements .x,.y,.z, like a dim3.

• Replace cuda API calls with Swan equivalents (See swan_api.h)

GENERATING CUDA / OPENCL EXECUTABLES

• For cross-compiling CUDA kernels to OpenCL: swan --opencl kernel.kh kernel.cu

• For compiling CUDA kernels to CUDA: swan --cuda kernel.kh kernel.cu

• For compiling OpenCL kernels to OpenCL: swan --opencl-direct kernel.kh kernel.cu

  This will produce a source code header file that contains a binary object containing the compiled kernel source and a set of functions for calling the kernels.

• Compile

• Link against the appropriate swan library (libswan_ocl or libswan_cuda).