[GRASS-dev] openMP support in GRASS GIS

[Moritz Lennert]

Thanks Maris,

[BTW: your mail was sent only to me, so I'm forwarding to the list.]

On 04/08/17 16:04, Maris Nartiss wrote:
> 1. It is not a dependency, as OpenMP code should run just fine also
> when compiled without OpenMP. Those are just comments in code thus
> backwards safe.

Right. I now see that all code is conditionalized on _OPENMP being set 
and I suppose that happens when you use --with-openmp as a compiler switch ?

> 2. It is not as easy as it seems, as every place, where
> parallelisation is introduced, needs to be examined carefully to not
> introduce hard to track issues when common variables are changed and
> to not make even worse performance by making CPU cache dirty when it
> isn't. Of course these problems affect only binaries compiled with
> OpenMP. Thus OpenMP support in GRASS GIS could be marked as "use at
> own risk".
> 

This thus means that merging the OpenMP version into the trunk version 
will not have any consequences for the "normal" user. However, does it 
mean that maintenance of the modules will become more complex ?

I see that in v.surf.rst the OpenMP stuff has already been integrated. 
It's only been 7 months, but up to now noone has complained, so I think 
we could integrate openmp into the two other modules as well (r.sun + 
r.sim.water).

Moritz