[gmx-developers] MPI with or without OpenMP

Berk Hess hess at kth.se
Thu Apr 23 13:58:42 CEST 2015

On 2015-04-23 13:48, Dominik 'Rathann' Mierzejewski wrote:
> 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.
This looks like an incorrect test setup, not an actual bug in the code.


> 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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