[J3] Performance Portability and Fortran: Making Fortran cool again

[William Clodius]

> On Jan 16, 2019, at 10:24 AM, Bill Long via J3 <j3 at mailman.j3-fortran.org> wrote:
> 
> Hi Ondrej,
> 
> This sort of insight is very valuable. Thanks for posting it. 
> 
> There seems to be a lot of focus on using GPU’s.  (Maybe that’s why they asked Gary -who works for NVIDIA - to participate?)
> 
> I would point out that a DO CONCURRENT construct has semantics that are quite compatible with execution on a GPU.   Typically, DO CONCURRENT constructs are threaded, using the same underlying infrastructure as OpenMP.  I’ve mentioned to our compiler developers about adding GPU support, but the chicken-egg problem is “no customer is asking for this”.  If customers, especially ones as large and visible as LANL, ask, you might get.   If the standard needs tweaks to better enable GPU execution of DO CONCURRENT, that is something we should look into. 
<snip>

What might work for GPUs is defining a special REAL kind, say FASTREAL, that maps to the fastest performing components of the processor. This could default to REAL32 if the system doesn’t have a GPU or other enhanced speed sub-processor.