[gmx-developers] MPI with or without OpenMP

[Dominik 'Rathann' Mierzejewski]

Hi, Berk.

On Thursday, 23 April 2015 at 10:42, Berk Hess wrote:
> On 04/23/2015 10:19 AM, Dominik 'Rathann' Mierzejewski wrote:
> >I'm the new maintainer of Fedora packages of GROMACS.
> >
> >What is your recommendation regarding MPI-enabled builds:
> >should I compile with thread-level (OpenMP) parallelization
> >enabled or not?
> >
> >In another package I maintain, cp2k, there are separate builds
> >with and without OpenMP.
> >
> >Also, what is the relation between GMX_THREAD_MPI and GMX_OPENMP?
> >I guess both should not be enabled at the same time.
>
> Always compile Gromacs with OpenMP. The user can decide at runtime to use
> one or more OpenMP threads. Using one thread will not result in measurable
> overhead compared to a non-OpenMP build.
> Thread-MPI is our own drop-in thread based MPI implementation, which is
> designed to work together with OpenMP.
> 
> So make two builds:
> Thread-MPI + OpenMP
> MPI + OpenMP

Thanks for the advice. I'll keep the current configuration, then.

I'm still hitting a bug in double-precision rounding on i686 (issue #1716),
but this is of little concern as almost everyone is probably using Gromacs
on x86_64.

Otherwise, the current version (5.0.4) seems to be working fine and the
internal testsuite passes. The next step will be to run your gerrit
testsuite as part of the build process to get greater code path testing
coverage. I wanted to get the new version out first in Fedora
development branch (rawhide), because the previous version was 4.6.5...

Regards,
Dominik
-- 
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