Stefan Mileschin

We had previously reported that Android 4.2 firmwares for Nexus 10 and Nexus 4 were found to contain OpenCL drivers. The drivers were an internal implementation detail and not officially supported for use by developers, and we had mentioned that the drivers may be removed in future updates. Android 4.3 is now rolling out to these devices and OpenCL drivers are no longer present in the new update.

OpenCL is an API for parallel and heterogeneous computing defined by Khronos, the same group that also stewards OpenGL. On the desktop and server side, AMD, Intel and Nvidia (and some others, such as Altera) support OpenCL on Windows and Linux. Apple in particular heavily pushes OpenCL on OSX and is providing drivers for latest version of OpenCL (1.2) in OSX Mavericks for all shipping Macs. Mobile hardware vendors including Qualcomm, ARM and Imagination Technologies tout OpenCL readiness for their hardware, but without shipping drivers on commercial devices, it is not possible to use OpenCL. Google is pushing their own proprietary solution called Renderscript on Android.

At a very high level, Renderscript is to OpenCL as Java is to C+Assembly. Renderscript is meant to be portable to any Android device irrespective of underlying hardware and does not expose lower level details of the hardware to the programmer. For example, Renderscript does not allow the programmer to choose whether a particular piece of code should run on the CPU, GPU or DSP etc. Such decisions are taken automatically by the Renderscript driver provided on the Android device. Renderscript's approach promotes portability and ease of use but there maybe a (potentially large) performance cost compared to well-optimized code in a lower-level language. Renderscript Compute has some other shortcomings such as lack of interoperability with graphics and lack of support in the Android NDK. The lack of programmer control, associated potential performance costs and other limitations make it unsuitable for some applications such as high performance game engines. Renderscript should be fine for some applications such as some of the simpler image processing filter applications and indeed Google is promoting Filterscript, a subset of Renderscript, which particularly targets image processing type applications.

http://www.anandtech.com/show/7191/a...opencl-drivers