[MPICH] MPI-IO, vector dataype

[Russell L. Carter]

Question about running multiple procs on a single
machine.  There appears to be no way to do this
with mpd, and from what I gather, gforker is the
right way to go but requires rebuilding mpi and
setting up some path munging scripts to differentiate
between mpd and gforker mpiexec bins.  Is that
correct?

Just to see if I understand, let me see if
I can summarize your explanation below.

Rajeev Thakur wrote:
>> Given (just the relevant code snippets)
>>     nprocs = 2, FILESIZE = 256,  INTS_PER_BLK = 4,
>>     bufsize(FILESIZE/nprocs), nints(bufsize/sizeof(int)),
>>
>>    filetype.Create_vector(nints/INTS_PER_BLK, INTS_PER_BLK,
>>                           INTS_PER_BLK * nprocs);
>>
>>    which works out to  Create_vector(4, 8, 16)  (intrinsic 
>> type MPI_INT)
> 
> Should be (8, 4, 8)

So we want to write a file of 256 bytes/64 ints, by
having 2 procs write 32 ints in 4 blocks of 8 ints each,
each proc writing into alternating blocks.

So the "count" argument is the total number of blocks
written by all of the procs?

The prototype indicates the arguments are (int count, int blocklength,
int stride)

>  
>>    f.Set_view(INTS_PER_BLK*sizeof(int)*myrank, MPI_INT,
>>                     filetype, "native", MPI_INFO_NULL);
>>
>>    which works out to Set_view(32 or 0 bytes, ...)

> Should be (16 or 0 bytes, ...)

If the blocksize is 8, and the displacement is in bytes "(Always bytes!)",
and we want the procs to write alternate blocks, so that the rank 1 proc
first writes into the second block, how can the displacement be anything
other than 32/0?

At any rate, these suggestions fail similarly as before, so now I'm looking
into reproducing the problem on a non pvfs2 file system.

Thanks,
Russell

> 
> Rajeev
> 


-- 
Russell L. Carter
Esturion, LLC
2285 Sandia Drive
Prescott, Arizona 86301

rcarter at esturion.net
928 308-4154