Re: [gomp4 0/8] NVPTX: initial OpenMP offloading

[Bernd Schmidt <bschmidt at redhat dot com>]

On 09/23/2015 07:22 PM, Alexander Monakov wrote:
> This patch series implements some minimally required changes to have OpenMP
> offloading working for NVPTX target on the gomp4 branch.  '#pragma omp target'
> and data updates should work, but all parallel execution functionality remains
> stubbed out (uses of '#pragma omp parallel' in target regions yield a link
> error).
>
> I'd like to get feedback on the patches, and approval for the gomp-4_0-branch
> where possible.

I have two major concerns here. Can I ask you how much experience you 
have with GPU programming and ptx? These patches provide stub 
functionality, which is easy enough, but I can't tell whether there's a 
credible plan to provide a full implementation. GPUs really need a 
different programming model than normal CPUs, which is something I 
learned the hard way, and I'm not terribly optimistic about porting 
libgomp to ptx. (I may be wrong.)

In one patch you mention newlib pthread type definitions - are you aware 
that there is no real pthreads implementation in the ptx newlib? The ptx 
newlib is really only provided for a minimal subset of libc functionality.

My other concern would be not to approve changes to the gomp-4_0-branch 
that could derail or slow down the effort to implement OpenACC, which 
has a much better chance of being in gcc-6 than this effort. You might 
want to make a private branch for your work.


Bernd