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

[Jeff Hammond]

If you use MPI_CHAR or MPI_BYTE, make sure the original count of int64_t is less than 128*1024*1024 and do an explicit cast on the buffer pointer so than MPICH Clang type checking won't complain. 

Jeff

Sent from my iPhone

> On Dec 24, 2013, at 6:41 AM, Erik Lindahl <erik.lindahl at scilifelab.se> wrote:
> 
> Hi,
> 
> Hm - good point. However, can’t we simply ask the MPI library to transport 8 chars instead in that case? (assuming that the endian is the same on all nodes in an MPI job)
> 
> Cheers,
> 
> Erik
> 
>> On 24 Dec 2013, at 13:34, Mark Abraham <mark.j.abraham at gmail.com> wrote:
>> 
>> 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
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