OpenCL On Linux Is Still Not Too Easy, Widespread

While there's OpenCL drivers available for Linux, on Ubuntu there is no OpenCL driver shipped by default and the proprietary driver implementations aren't always great.

Intel has their closed-source OpenCL SDK for the CPU, AMD has their OpenCL support in the Catalyst driver, and NVIDIA has their OpenCL/CUDA support bundled within their binary driver. When it comes to open-source support, the Gallium3D OpenCL support is still primitive and isn't shipped by default. Intel has the Beignet project for open-source OpenCL but that's even worse off than the Gallium3D OpenCL support.

For details on the experiences of using OpenCL on Ubuntu 13.04 and other information, an open-source developer, Michal Hruby, has written about it on his blog.