2017-01-14 GPU and pycuda or pyopencl on Windows

pycuda is a python module implemented to use GPU. On Windows, the best way to install it is to get it from Unofficial Windows Binaries for Python Extension Packages. The module requires Visual Studio Community Edition and CUDA Toolkit. Once it is done, you can try the following program to test your installation:

from pycuda.compiler import SourceModule
mod = SourceModule("""
__global__ void multiply_them(float *dest, float *a, float *b)
  const int i = threadIdx.x;
  dest[i] = a[i] * b[i];

multiply_them = mod.get_function("multiply_them")

a = numpy.random.randn(400).astype(numpy.float32)
b = numpy.random.randn(400).astype(numpy.float32)

dest = numpy.zeros_like(a)
        drv.Out(dest), drv.In(a), drv.In(b),
        block=(400,1,1), grid=(1,1))


If it fails due to the following error:

ImportError: DLL load failed: Le module spécifié est introuvable.

It probably means the DLL nvcuda.dll is missing. You can use dependency walker to look at the DLL dependencies for a specific DLL (files .dll or *.pyd if they are compiled with Python). In that case, this means the drivers for the graphics card is missing. You first need to check your card. If you realise your card is not NVidia, you can stop: pycuda only works with a NVidia card. Mine is a *Intel Graphics 4000 and I downloaded the drivers from this location: Intel® Graphics Driver for Windows® 10 and Windows 7*/8.1* [15.33]. In that case, you will need to switch to pyopencl. You can still get it from Unofficial Windows Binaries for Python Extension Packages.

Finally, you should get the same OpenCL library used to compile pyopencl which Intel OpenCL. You might also need Windows 10 SDK. Finally, you need to choose the backend for pyopencl:

import pyopencl as cl
ctx = cl.create_some_context()

Follow the questions and choose the graphics card as the backend. Setup the following environment variable to skip the questions next time:

import os
os.environ["PYOPENCL_CTX"] = '0:1'


If you want to use theano on GPU, you need TDM-GCC 64bit but theano only supports NVidia cards. The documentation tells it will support opencl soon: GpuArray Backend.