[Pkg-opencl-devel] opencl-icd selection

[Rebecca N. Palmer]

> Would it be possible to specify the dependencies in such a
> way that GPU-related ICDs are installed only if the corresponding mesa
> packages are already installed (or would be otherwise installed anyway
> in this run)?
No, and it would be mostly pointless anyway as the video drivers also 
default to installing them all ( 
https://packages.debian.org/sid/xserver-xorg ): if a user cares enough 
about saving space/bandwidth to manually pick one video driver, they can 
also manually pick one ICD, which will then satisfy dependencies on 
opencl-icd because of the Provides: ( 
https://www.debian.org/doc/debian-policy/ch-relationships.html#s-virtual ).

> I think that just extending ocl-icd to have a smarter default context
> selection (and possibly ICD ordering) would fix it. My idea is the
> following:
The applications I checked weren't passing NULL platform (probably 
because, as you note, this doesn't work on all ICD loaders): they were 
either explicitly picking the first platform, or treating any error 
(including CL_DEVICE_NOT_FOUND) when iterating over platforms as fatal. 
  Hence, it's the platform order that most needs changing.

> We should probably discuss this with the ocl-icd authors too.
ocl-icd's maintainer is Vincent Danjean, who has previously agreed in 
principle that this is a good idea: 
http://lists.alioth.debian.org/pipermail/pkg-opencl-devel/Week-of-Mon-20140203/000079.html

> Ideally, it would be nice if mesa-opencl-icd included support for CPU
> devices as well (or does it, and I didn't know about it?)
It's nominally on their todo list ( 
http://dri.freedesktop.org/wiki/GalliumCompute/ ), as is an open-source 
replacement for nvidia-opencl-icd, but I don't know if anyone is 
actively working on either.