Screenshot from Intel’s “God Rays” demo

This article is still work-in-progress

Intel has just released its OpenCL bit CPU-drivers, version 2013 bèta. It has support for OpenCL 1.1 (not 1.2 as for the CPU) on Intel HD Graphics 4000/2500 of the 3rd generation Core processors (Windows only). The release notes mention support for Windows 7 and 8, but the download-site only mentions windows 8. Support under Linux is limited to 64 bits.

The release notes mention:

• General performance improvements for many OpenCL* kernels running on CPU.
• Preview Tool: Kernel Builder (Windows)
• Preview Feature: support of  kernel source code hotspots analysis with the Intel VTuneT Amplifier XE 2011 update 3 or higher.
• The GNU Project Debugger (GDB) debugging support on Linux operating systems.
• New OpenCL 1.2 extensions supported by the CPU device:
  • cl_khr_int64_base_atomics and cl_khr_int64_extended_atomics
  • cl_khr_fp16
  • cl_khr_gl_sharing
  • cl_khr_gl_event
  • cl_khr_d3d10_sharing
  • cl_khr_dx9_media_sharing
  • cl_khr_d3d11_sharing.
• OpenCL 1.1 extensions that were changed in OpenCL 1.2:
  • Device Fission supports both OpenCL 1.1 EXT API’s and also OpenCL* 1.2 fission core features
  • Media Sharing support intel 1.1 media sharing extension and also the 1.2 KHR media sharing extension
  • Printf extension is aligned with OpenCL 1.2 core feature.

Check the release notes for full information.

The drivers can be found on http://software.intel.com/en-us/articles/vcsource-tools-opencl-sdk-2013/. Installation is simple. For Windows there is a installer. If you have Linux, make sure you remove any previous version of Intel’s openCL drivers. If you have a Debian-based Linux, use the command ‘alien’ to convert the rpm to deb, and make sure ’libnuma1‘ is installed. There are requirements for libc 2.11 or 2.12 – more information on that later as Ubuntu 12.04 has libc6 2.15.

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Programmers know the value of everything and the costs of nothing. I saw it a while back and loved it immediately. The quote by Alan Perlis is originally about Perl-programmers, but only highly trained HPC-programmers seem to have obtained this basic knowledge well. In an interview with Andrew Richards of Codeplay I heard it from another perspective: software languages were not developed in a time that cache was 100 times faster than memory. He claimed that it should be exposed to the programmer what is expensive and what isn’t. I agreed again and hence this post.

I think it is very clear that programming languages (and/or IDEs) need to be redesigned to overcome the hardware-changes of the past 5 years – I talked about that in the articles “Separation of compute, control and transfer” and “Lots of loops“. But it does not seem to be enough. So what are the costs of each operation (on CPUs)?

This article is just to help you on your way, and most of all: to make you aware. So note it is incomplete and probably not valid for all kinds of CPUs.

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Typos are a programmers worst nightmare, as they are bad for concentration. The code in your head is not the same as the code on the screen and therefore doesn’t have much to do with the actual problem solving. Code highlighting in the IDE helps, but better is to use the actual OpenCL compiler without running your whole software: an Online OpenCL Compiler. In short is just an OpenCL-program with a variable kernel as input, and thus uses the compilers of Intel, AMD, NVidia or whatever you have installed to try to compile the source. I have found two solutions, which both have to be built from source – so a C-compiler is needed.

• CLCC. It needs the boost-libraries, cmake and make to build. Works on Windows, OSX and Linux (needs possibly some fixes, see below).
• OnlineCLC. Needs waf to build. Seems to be Linux-only.

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Disclaimer: I am not a lawyer and below is my humble opinion only. The post is for insights only, not for legal matters.

GPL was always a protection that somebody or some company does not run away with your code and makes the money with it. Or at least force that improvements get back into the community. For unprepared companies this was quite some stress when they were forced to give their software away. Now we have host-kernels-languages such as OpenCL, CUDA, DirectCompute, RenderScript don’t really link a kernel, but load it and launch it. As GPL is quite complicated if it comes to mixing with commercial code, I try to give a warning that GPL might not be prepared for this.

If your software is dual-licensed, you cannot assume the GPL is not chosen when eventually used in commercial software. Read below why not.

I hope we can have a discussion here, so we get to the bottom of this.

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In the series Basic Concepts I try to give an alternative description to what is said everywhere else. This time my eye fell on alternative convenience methods in two cases which were introduced there to be nice to devs with i.e. C/C++ and/or graphics backgrounds. But I see it explained too often from the convenience functions and giving the “preferred” functions as a sort of bonus which works for the cases the old functions don’t get it done. Below is the other way around and I hope it gives better understanding. I assume you have read another definition, so you see it from another view not for the first time.

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August 2012: article has been completely rewritten and updated

Want to have both your GTX and Radeon working as OpenCL-devices under Linux? The bad news is that attempts to get Radeon as a compute device and the GTX as primary all failed. The good news is that the other way around works pretty easy (with some luck). You need to install both drivers and watch out that libglx.so isn’t overwritten by NVidia’s driver as we won’t use that GPU for graphics – this is also the reason why it is impossible to use the second GPU for OpenGL.

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