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Subject: Re: [OMPI devel] max. message size
From: Paul Kapinos (kapinos_at_[hidden])
Date: 2013-07-08 09:20:34


Mr mohammad assadsolimani,

1. your questions belongs to the 'OMPI users' mailing list, this one is for
developers.

2. in MPI, the input parameters are defined to be integers.
Integers usually are 32bit long (unless you use ILP64 instead of LP64, what is
still unusual). So I swear, your program send the messages as byte sequences and
thus cannot send more than 2^31 (=2Gb) in one call. Possible solutions:
- send data in chunks
- use ILP64 (no idea about Open MPI support it)
- use constructed data types instead of "bytes". (using doubles istead of
sending the same data as byte sequence lead to 8x raise of the max message size).

see also
http://montecarlo.vtt.fi/mtg/2012_Madrid/Hans_Hammer2.pdf
esp. pp. 6 - 7.

Best

Paul

On 07/08/13 15:08, mohammad assadsolimani wrote:
>
> Dear all,
>
> I do my PhD in physics and use a program, which uses openmpi for
> a sophisticated calculation.
> But there is a Problem with "max. message size ". That is limited to ~2GB.
> I do not know how is called it exactly?!
> Is there any possibility to extend this memory size?
>
> I am very grateful for all of your help and thank you in advanced
> Mohammad
>
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-- 
Dipl.-Inform. Paul Kapinos   -   High Performance Computing,
RWTH Aachen University, Center for Computing and Communication
Seffenter Weg 23,  D 52074  Aachen (Germany)
Tel: +49 241/80-24915