[mpich2-dev] Fw: 32-bit ROMIO: What is the best solution?

[Brian Smith]

That's basically what we are doing. The problem is, there are a large 
number of places throughout the code (not just in ROMIO) where there are 
casts that assume MPI_Aint == sizeof(void*)==sizeof(int*)==sizeof(int), so 
we are walking through all that code and seeing what the casts are doing 
and fixing them as appropriate.


Brian Smith
BlueGene MPI Development
IBM Rochester
Phone: 507 253 4717
smithbr at us.ibm.com




William Gropp <gropp at mcs.anl.gov> 
Sent by: owner-mpich2-dev at mcs.anl.gov
02/29/2008 10:16 AM
Please respond to
mpich2-dev at mcs.anl.gov


To
Bob Cernohous/Rochester/IBM at IBMUS
cc
mpich2-dev at mcs.anl.gov
Subject
Re: [mpich2-dev] Fw: 32-bit ROMIO: What is the best solution?






One thing that we've talked a little about is providing an option to make 
MPI_Aint and MPI_Offset the same (large) size, even if sizeof(void*) < 
sizeof(MPI_Aint).  Does it make sense to make this the option (Aint and 
Offset the same size) and then make everything else match up with that 
(still as an option, since there are costs to making Aints bigger than 
pointers).  

Bill

On Feb 28, 2008, at 4:21 PM, Bob Cernohous wrote:


I'm moving a discussion here from the IBM/Argonne open source DCMF mailing 

list (http://dcmf.anl-external.org/wiki). 

Very briefly, we're making MPI_Aint into a 64 bit signed value on 
32-bit MPICH2/ROMIO platforms.  This will fix problems with files larger 
than 2G (and possibly other 4G virtual address problems). 

We'd like to start sending fix patches to the mpich-dev community for 
comment. 

The code base that we're patching is changing under us.  So our patches 
might not apply properly for members of this list.  When we're done, we 
will have a patch for the current release of MPICH2.  For now, we'd like 
to provide these patches to the community for information and discussion. 

If you're interested, there might be more technical history in the DCMF 
archives.  Otherwise, start the discussion here. 

bobc at us.ibm.com wrote on 02/27/2008 04:19:29 PM:
> 
> bobc at us.ibm.com wrote on 02/08/2008 02:41:40 PM: 
> 
> >We all realize there are issues with MPI_Aint's in 32 bit 
implementations. 
> >Using signed 32 bit addresses along with 64 bit offsets can result in 
> >some pretty broken code.  I've reproduced several problems on 
> >BGL/BGP/linux.   The problems are most obvious with romio files > 2G or 

> >virtual addresses > 2G. 
> 
> Earlier this month I posted some comments to this mailing list about 
> 32-bit MPICH/ROMIO/MPI_Aint issues (see above and the archive).     
> 
> We've started to work on the problem.   We're (optionally) making 
> MPI_Aint a 64 bit signed value even when integers/pointers are 32 bit 
> values. 
> 

William Gropp
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign


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