[gmx-developers] new 64-bit int support and MPI

Jeff Hammond jeff.science at gmail.com
Tue Dec 24 16:11:34 CET 2013

MPI_INT64_T is what you use to send messages containing that C99 type. The MPI_LONG_LONG type should be supported prior to MPI-2.2 (sorry, I am not at my desk and cannot verify).

Because Microsoft doesn't support C99, you might fine they don't support MPI_INT64_T - maybe they do because it's in C++11 (?) - but I care far too little about Windows to investigate this. 

Do you intend to send messages with more than 2^31 elements? This is a very different issue. 

I have been working with other code teams on this for some time. What most people try to do is not consistent with the MPI standard and can lead to erroneous programs. 

Anyways, sorry for my ignorance, but I think you'll be fine with requiring MPI-2.2, as everyone has it, or at least the majority. OpenMPI might say they are only at 2.1, but I recall they are missing only one (useless) feature. 



Sent from my iPhone

> On Dec 24, 2013, at 7:04 AM, Alexey Shvetsov <alexxy at omrb.pnpi.spb.ru> wrote:
> Hi!
> Actually its not that hard to install fresh mpi library. Personally i run OpenMpi 1.6 installed in ${HOME} on rhel 4 cluster (that runs on xeon 53xx).
> Mark Abraham писал 24-12-2013 16:34:
>> Hi,
>> I'm happy with the recent change to requiring 64-bit integers, but I
>> note that this means we have required that the MPI library support the
>> MPI_INT64_T datatype from MPI 2.2. AFAIK that's probably OK in
>> practice, but I thought it worth mentioning / discussing.
>> We should update the install guide and add a CMake test for its
>> support, however, since there will still be plenty of people with
>> earlier non-compliant MPI libraries. I imagine CentOS will take about
>> 5 years to update that far...
>> Cheers,
>> Mark
> -- 
> Best Regards,
> Alexey 'Alexxy' Shvetsov
> Petersburg Nuclear Physics Institute, NRC Kurchatov Institute, Gatchina, Russia
> Department of Molecular and Radiation Biophysics
> Gentoo Team Ru
> Gentoo Linux Dev
> mailto:alexxyum at gmail.com
> mailto:alexxy at gentoo.org
> mailto:alexxy at omrb.pnpi.spb.ru
> -- 
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