[Paraview-developers] Using OpenMP for custom plugins/filters

[Schlottke-Lakemper, Michael]

Hi Utkarsh,

Thanks for the fast answer. I have a a few follow-up questions, if I may:

- What is the default SMP backend if I do not configure anything during ParaView compilation (I assume “Sequential”)?
- With OpenMP, will I have to call vtkSMPTools::Initialize(nThreads) explicitly with nThreads determined by myself, or will it honor e.g. OMP_NUM_THREADS automatically?
- If I have to call vtkSMPTools::Initialize(nThreads) explicitly, where should it be done in case of a plugin? In the plugin’s ctor, in the RequestData method, or someplace else?
- Am I correct in the assumption that the backend type should not change the results, i.e. that on hosts where I do not know which SMP backend is configured, I can assume my algorithms “just work”?

Thanks a lot in advance

Michael

> On 08 Mar 2016, at 14:39 , Utkarsh Ayachit <utkarsh.ayachit at kitware.com> wrote:
> 
> Michael,
> 
> The VTK-SMP approach is indeed the way to go for this. To make the
> backend use OpenMP, you simply compile VTK/ParaView with
> VTK_SMP_IMPLEMENTATION_TYPE set to OpenMP. The programming model
> described in the SMP Guide PDF has been implemented for all supported
> backends including OpenMP and TBB.
> 
> Utkarsh
> 
> On Tue, Mar 8, 2016 at 6:22 AM, Schlottke-Lakemper, Michael
> <m.schlottke-lakemper at aia.rwth-aachen.de> wrote:
>> Hi everyone,
>> 
>> We have a custom parallel reader plugin that works well with our files even
>> on large-ish (100-1000) number of cores for the pvserver. Recently we’ve
>> added the capability to also create ghost cells with this reader such that
>> MPI domain boundaries become transparent to filters that need neighbor data,
>> e.g., for gradient computations. However, this ghost cell generation takes
>> up quite some time, so we would like to keep the number of MPI ranks at a
>> minimum and use hybrid MPI-OpenMP parallelism for our plugin.
>> 
>> My question is thus if it is possible to use OpenMP inside a custom plugin?
>> And if yes, is there a canonical way to do it (maybe an example plugin) or
>> is it going to be a hack?
>> 
>> When searching the interwebs for ParaView and OpenMP, I only came up with an
>> old VTK mailing list thread from 2014
>> (http://public.kitware.com/pipermail/vtkusers/2014-March/083399.html), in
>> which David (DeMarle) refers to some initial documentation of the SMP
>> framework (http://www.vtk.org/Wiki/images/3/3b/VTK_SMP_Guide.pdf). However,
>> the linked PDF does not contain references to OpenMP.
>> 
>> Thanks a lot in advance!
>> 
>> Michael
>> 
>> --
>> Michael Schlottke-Lakemper
>> 
>> Chair of Fluid Mechanics and Institute of Aerodynamics
>> RWTH Aachen University
>> Wüllnerstraße 5a
>> 52062 Aachen
>> Germany
>> 
>> Phone: +49 (241) 80 95188
>> Fax: +49 (241) 80 92257
>> Mail: m.schlottke-lakemper at aia.rwth-aachen.de
>> Web: http://www.aia.rwth-aachen.de
>> 
>> 
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