<p>Under Windows and Mac the Intel GPU drivers include OpenCL support; however, on Linux OpenCL on Intel GPUs is implemented through an open source project called <a href="http://www.freedesktop.org/wiki/Software/Beignet/">Beignet</a> (pronnounced like "ben yay", a type of <a href="http://en.wikipedia.org/wiki/Beignet">French pastry</a> akin to a what we would call a "fritter" in English). Below I have written a step-by-step guide on how you can get Beignet running on an Ubuntu 14.10 system which has an Intel 3rd, 4th, or fifth generation Intel processor. Instructions for other variants of Linux will be similar, except for the commands to install the prerequisite packages.</p>

<p>There are several little caveats which need to be discussed up front. Foremost the Beignet project supports the following hardware:</p>

<ul>
<li>3rd Generation Intel Core Processors</li>
<li>Intel “Bay Trail” platforms with Intel HD Graphics</li>
<li>4th Generation Intel Core Processors (requires a kernel patch be applied for shared memory!)</li>
<li>5th Generation Intel Core Processors "Broadwell".</li>
</ul>

<p>There are also a few noteworthy issues of which you should be aware:</p>

<ul>
<li><p>If your computer is running a Linux kernel in the 3.15 or 3.16 branch, you will need to disable some register whitelist functionality every time you reboot your system. This can be accomplished by running <code>echo 0 &gt; /sys/module/i915/parameters/enable_cmd_parser</code> as root.</p></li>
<li><p>4th Generation Intel Processors (i.e. i3/5/7-<em>4</em>xxx) require a kernel patch for shared/local memory to function.</p></li>
<li><p>There is no double precision support</p></li>
<li><p>OpenGL-OpenCL interop via <code>cl_khr_gl_sharing</code> is not supported</p></li>
</ul>

<p>There are additional release notes that can be found on the <a href="http://www.freedesktop.org/wiki/Software/Beignet/">Beignet</a> project page.</p>

<h3>Installing prerequisites</h3>

<pre><code>sudo apt-get install build-essential g++ cmake 
sudo apt-get install clang libclang-3.5-dev libclang-dev libclang1
</code></pre>

<p>Note, if you are on a Ubuntu 14.04 system, you should install <code>libclang-3.4-dev</code> instead then run <code>update-alternatives</code> to point <code>llvm-link</code> and <code>llvm-as</code> to the correct version. The latter can be accomplished using the following commands:</p>

<pre><code>sudo update-alternatives --install /usr/bin/llvm-link llvm-link /usr/bin/llvm-link-3.4 34
sudo update-alternatives --install /usr/bin/llvm-as llvm-as /usr/bin/llvm-as-3.4 34
</code></pre>

<p>If you want to use the standard OpenCL ICD loader, you will also need to install these packages:</p>

<pre><code>sudo apt-get install opencl-headers ocl-icd-dev ocl-icd-libopencl1
</code></pre>

<p>I would also recomment you install the <code>clinfo</code> program so that you can verify that your installation is successful:</p>

<pre><code>sudo apt-get install clinfo
</code></pre>

<h3>Round 1: checkout and compile Beignet</h3>

<pre><code>git clone git://anongit.freedesktop.org/beignet
cd beignet
git checkout Release_v1.0.0
mkdir build
cd build
cmake ..
</code></pre>

<p>During the CMake stage, ensure that the OCL ICD header file is installed otherwise the library will not create an installable client driver. If everything went fine, go ahead and compile the source and install the library</p>

<pre><code>make
</code></pre>

<p>(Note, you can do make -jN with N > 1 to do a parallel build.)<br />
Next we verify that Beignet is functioning correctly on your hardware by running unit tests. These can be found in the <code>utest</code> folder. The unit tests require some enviornmental variables be set prior to invocation:</p>

<pre><code>cd utests
cat setenv.sh
[copy all of the export commands, run them in your shell]
./utest_run
</code></pre>

<p>If a significant fraction of the unit tests fail and you have a 3.15 or 3.16 kernel, you need to disable register whitelisting using a command similar to the following:</p>

<pre><code>sudo su
echo 0 &gt; /sys/module/i915/parameters/enable_cmd_parser
exit
</code></pre>

<p>and try re-running the tests. Please note that this change is not permanent and you will need to re-run it if you reboot your system. Alternatively, you could add this command to a startup script. The Beignet release notes mention there is a kernel patch to fix this issue which you could backport if you so desired.</p>

<p>If most of the tests pass, but those that involve local memory (~20-30 of the tests) fail, you will need to apply the <a href="#kernel-patch">kernel patch</a> listed below.</p>

<p>If all was well, install Beignet to your system:</p>

<pre><code>sudo make install
</code></pre>

<p>You can see a list of installed software in the <code>install_manifest.txt</code> file in the build directory.</p>

<h3>Verify Beignet is installed</h3>

<p>In a terminal run the <code>clinfo</code> program. You should see something like this:</p>

<pre><code>$ clinfo
...      
Platform Name:              Intel Gen OCL Driver
Number of devices:          1
Device Type:                CL_DEVICE_TYPE_GPU
...
Name:                       Intel(R) HD Graphics Haswell GT2 Desktop
Vendor:                     Intel
Device OpenCL C version:    OpenCL C 1.2 beignet 0.9.1
Driver version:             0.9.1
Profile:                    FULL_PROFILE
Version:                    OpenCL 1.2 beignet 0.9.1
Extensions:                 cl_khr_global_int32_base_atomics 
                            cl_khr_global_int32_extended_atomics 
                            cl_khr_local_int32_base_atomics 
                            cl_khr_local_int32_extended_atomics 
                            cl_khr_byte_addressable_store cl_khr_icd
</code></pre>

<p>Take note that the Intel OpenCL driver is loaded for a GPU device using <code>beignet</code>. This indicates the Installable Client Driver (ICD) is correctly installed. Also note the extensions listed.</p>

<h3>Applying the kernel patch to enable OpenCL shared local memory.</h3>

<p>If you are using Beignet on a 4th generation Intel processor, you will need to apply a kernel patch to enable shared/local memory. This is a fairly lengthy process that will require at least 70 GB of hard disk space and perhaps an hour of compilation time if the build is executed in parallel.</p>

<p>In the next few paragraphs I'll walk you through how you can apply the kernel patch. I have based my instructions on the &#91;kernel compliation instructions for Ubuntu&#93; (https://help.ubuntu.com/community/Kernel/Compile). Instructions for other variants of Linux will be significantly different</p>

<p>Install prerequisites:</p>

<pre><code>sudo apt-get build-dep linux-image-`uname -r`
</code></pre>

<p>Make a working directory for the kernel somewhere and download the source</p>

<pre><code>mkdir kernel
cd kernel
apt-get source linux-image-`uname -r`
</code></pre>

<p>Next we see if we can automatically apply the patch. First download the patch:</p>

<pre><code>wget https://01.org/sites/default/files/disable-batchbuffer-security.patch
</code></pre>

<p>Now <code>cd</code> into the kernel directory:</p>

<pre><code>cd linux-3.13.0
</code></pre>

<p>Check some details about the patch</p>

<pre><code>git apply --stat ../disable-batchbuffer-security.patch
</code></pre>

<p>Try automatically applying the patch:</p>

<pre><code>git apply --check ../disable-batchbuffer-security.patch
</code></pre>

<p>If it automatically applies with no errors, just apply it:</p>

<pre><code>git apply ../disable-batchbuffer-security.patch
</code></pre>

<p>If it did not work (as was the case on my system), the change is fairly simple. Open the <code>drivers/gpu/drm/i915/i915_gem_execbuffer.c</code> file in an editor:</p>

<pre><code>gedit drivers/gpu/drm/i915/i915_gem_execbuffer.c
</code></pre>

<p>In the <code>i915_gem_do_execbuffer</code> function, find the following code:</p>

<pre><code>flags = 0;
if (args-&gt;flags &amp; I915_EXEC_SECURE) {
    if (!file-&gt;is_master || !capable(CAP_SYS_ADMIN))
        return -EPERM;
</code></pre>

<p>And add the line <code>flags |= I915_DISPATCH_SECURE;</code> as follows:</p>

<pre><code>flags = 0;
flags |= I915_DISPATCH_SECURE;
if (args-&gt;flags &amp; I915_EXEC_SECURE) {
    if (!file-&gt;is_master || !capable(CAP_SYS_ADMIN))
        return -EPERM;
</code></pre>

<p>This was inserted on line 998 for me. Save the file. Now we need to compile and install the modified kernel.</p>

<p>Now we build the new kernel. Run the following commands from within the kernel source directory:</p>

<pre><code>fakeroot debian/rules clean
DEB_BUILD_OPTIONS=parallel=8 fakeroot debian/rules binary-headers binary-generic
</code></pre>

<p>This will build some Debian packages and place them in the directory <em>above</em> the kernel source root.</p>

<p>After the kernel has compiled, install it:</p>

<pre><code>cd ../ (or go back into the kernel directory)
sudo dpkg -i linux-headers-3.16.0-29-generic_3.16.0-29.54_amd64.deb 
sudo dpkg -i linux-image-3.16.0-29-generic_3.16.0-29.54_amd64.deb
</code></pre>

<p>(you might have to change the numeric kernel version to match what you compiled) Now add the kernel to the boot options:</p>

<pre><code>sudo update-grub
sudo reboot
</code></pre>

<p>Now go back and re-run the Beignet unit test framework from above. With any luck everything will work fine.</p>
