[arch-dev-public] Bringing libcl 1.2 into Arch

[Sven-Hendrik Haase]

On 23.05.2014 14:17, Lukas Jirkovsky wrote:
> Hello,
> I've been toying with the idea of bumping libcl from version 1.1 to
> 1.2. Bellow I will sum up my findings.
>
> Current State
> -------------------
> The opencl support is split into three different packages:
>
>   * opencl-headers - provides header files necessary for compilation,
> currently at version 1.1
>
>   * libcl - provides libCL.so which is an ICD loader, ie. this
> libraryis used to the actual OpenCL implementation depending on the
> user needs. In arch we use proprietary libcl from the nVidia drivers.
> Because nVidia supports only OpenCL 1.1 our library does, too.
>
>   * opencl-nvidia - an OpenCL implementation. There are packages in
> AUR that provide the implementation for other vendors, too, such as
> intel-opencl-sdk
>
> There are two main reasons why our OpenCL support is stuck at 1.1:
>   * when the OpenCL support was introduced, libcl was only provided by
> nVidia and AMD as part of their proprietary drivers, but AMD binary
> drivers are not supported
>   * nvidia supports only OpenCL 1.1
>
> Proposed Changes
> ----------------------------
> The time has changed and now there are two opensource ICD loaders available:
>   * ocl-icd (https://aur.archlinux.org/packages/ocl-icd/)
>   * opencl-icd (https://aur.archlinux.org/packages/opencl-icd/)
> Both ICD loaders provide libCL.so in version 1.2. Both ICD loaders are
> drop-in replacements for the current libcl, ie. no rebuild is needed.
>
> I propose the following changes:
>   1. Update the opencl-headers to 1.2 (again). There is a package
> opencl-headers12 that grabs them from svn.
>   2. replace libcl with either ocl-icd or opencl-icd
>
> Reasons for change:
>   * replace proprietary libCL.so with an open source one
>   * support for OpenCL 1.2. While nVidia doesn't support this, it will
> allow using OpenCL 1.2 features on devices that support it (Intel
> CPU's, AMD GPU's) which couldn't have been used before as they were
> not provided by libCL
>
> Possible Problems
> ---------------------------
> So far I was able to find only one possible problem. Applications
> using OpenCL has to check for the supported OpenCL version on runtime.
> However, if an application does the check only on compile time, it
> will crash. IIRC this used to be a problem with luxmark, but I tested
> it and it works correctly now. I have also tested imagemagick and
> blender and both work fine. Well, blender is broken for me, but it was
> before, too. At least it doesn't crash.
>
> In more detail, the reason is that you can compile OpenCL 1.2
> application without problems even on OpenCL 1.1 system as the
> libraries and headers will now provide everything needed. However, if
> the application tries to call an OpenCL 1.2 function, the driver will
> not provide it, in which case it will crash.
>
> In any case if such issue arises, it needs to be fixed upstream.
>
> The BIG Question
> --------------------------
> We once had problem that there were no suitable ICD loaders part the
> one from nVidia. Now we have two. The question is which one to use.
>
>   * opencl-icd is the reference ICD loader from Khronos. It uses a
> custom license (or at least a license I don't know) which seems to
> forbid distributing of sources, but which explicitly allows
> redistribution of the compiled binaries
>
>   * ocl-icd is an independent project under 2-clause BSD license. I
> think from the two this one has longer development
>
> Lukas
+1 for the idea.

As for which loader to use, I have no idea. Pick the saner one.