OpenCL Fast Fourier Transform

Eric Bainville - May 2010

Introduction

In this article, we will experiment various OpenCL implementations of one-dimensional Fast Fourier Transform (FFT) algorithms.

This article is becoming rather long now. It was written in several sessions, interrupted by other higher priority tasks (i.e. paid contracts). The objective is to reach an FFT implementation in OpenCL with performances at least matching NVidia CUFFT, and running on both ATI and NVidia GPU's.

This objective is reached in the Radix 4,8,16,32 kernels page, using several chained calls of simple kernels not using shared memory. The experiments on kernels using shared memory are in progress, and the last two pages of the articles will be updated.

Contents

  1. Introduction - Introduction.
  2. DFT - Discrete Fourier Transform.
  3. FFT - Fast Fourier Transform algorithms.
  4. Reference implementations - FFTW, Intel MKL, and NVidia CUFFT.
  5. Radix-2 kernel - Simple radix-2 OpenCL kernel.
  6. Radix 4,8,16,32 kernels - Extension to radix-4,8,16, and 32 kernels.
  7. Radix-r kernels benchmarks - Benchmarks of the radix-r kernels.
  8. One work-group per DFT (1) - One DFT2r per work-group of size r, values in local memory.
  9. One work-group per DFT (2) - One DFT2r per work-group of size r, values in registers, transferts using local memory.

References

Benchmarks

Execution times are measured on the following hardware:


Q9550:

  Intel Core 2 Quad Q9550 (4 cores) @2.83 GHz (stock speed)

  Chipset Intel P45

  12GB of DDR2 @800 MHz

  Linux 64-bit kernel-2.6.32

  glibc-2.10.1 gcc-4.3.4 fftw-3.2.2 mkl-10.2.4.032



Core i7:

  Intel Core i7 920 (4 cores, 8 threads) @3.33 GHz (overclocked)

  Chipset Intel X58

  6GB of DDR3 @1.33 GHz

  Windows 7 Ultimate 64-bit

  vs-2010 mkl-10.2.4.032



GTX285:

  NVidia GTX285 1GB

  Chipset Intel P45

  Linux 64-bit kernel-2.6.32

  NVidia driver 195.36.24 + CUDA toolkit 3.0

  OpenCL compiler option -cl-fast-relaxed-math



HD5870:

  ATI Radeon HD5870 1GB

  Chipset Intel X58

  Windows 7 Ultimate 64-bit

  ATI Catalyst 10.5 + Stream SDK 2.1