[GRASS-dev] --with-opencl without a GPU

Hamish hamish_b at yahoo.com
Tue Jun 25 17:24:25 PDT 2013

Maciek wrote:

> If I wanted to build G7 --with-opencl on a machine with a 
> non-Intel/nVidia/AMD GPU would everything still build and work fine?

What other manufacturer(s) of GPUs are still in business?
The short answer is yes, as long as they provide a libOpenCL.so library
and C header files to go along with it.

> I only have Intel/nVidia machines so can't check this myself reliably I guess.

note that the intel i7 Ivy Bridge HD4000 driver only supplies OpenCL
multi-CPU core support for Linux. The same chip has a GPU driver for
MS Windows and I think Mac OSX. On Linux + Intel graphics you need
a Xeon chip for driver GPU support currently.

nVidia have shipped OpenCL support standard with their proprietary
Linux driver for a while now, although they advertise more about the
CUDA side of things.

> Would r.sun utilize more than 1 CPU (I mean once the GSoC OpenCL r.sun 
> stuff is merged into to G7 trunk) on such a machine?

I hope so, for Linux Ivy Bridge chips that's all you'd be able to get,
but running multi-core GPCPU is still a time win. I'm not sure if OpenCL
lets you do GPU+CPU or you have to choose one or the other, or if it
can do both at the same time if the CPU memory array size gets limited
by the GPU memory limit.

> Are the dependencies only the OpenCL headers and the libcl or something 
> more?

I think that's it, but I'm still learning.


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