On 07/20/2014 04:23 PM, Tom Rosmond wrote:
Hello,
For several years I have successfully used MPIIO in a Fortran global
atmospheric ensemble data assimilation system. However, I always
wondered if I was fully exploiting the power of MPIIO, specifically by
using derived data types to better describe memory and file data
layouts. All of my IO has been using elementary data types, e.g.
mpi_real, mpi_integer, for file 'datatype's, and numerous references
suggest that datatypes of derived data types could improve IO
performance.
Attached is a KSH script with an included fortran program of a very
simple example of what I am now doing successfully, and poses the
question why doesn't my attempt with a derived data type work. The
fortran program is well commented to explain each step. I run the
script on a 4 core linux workstation, and the example is setup for that
system. On a similar system just 'chmod' the script executable and run
it. The script will compile amd execute the program . It should first
show printed output from successful IO using my current approach, and
then aborts when trying my derived data type test. What am I doing
wrong? Any advice is appreciated.
Ah ha. I spent so much time looking at how ROMIO processed your
datatypes that I did not at first notice how you were using those
datatypes.
This works for you:
allocate(buffer(ijsiz(ir),numrec))
ioff = 0
lenij = ijsiz(ir)*numrec
call mpi_file_read_at_all(ifh,ioff,buffer,lenij,mpi_real,status,ierr)
but this does not:
ioff=0
lenij=1
call mpi_file_read_at_all(ifh,ioff,buffer,lenij,datatype,status,ierr)
The mistake is a natural one to make: the 'buffer, count, datatype'
tuple passed to the read commands (and passed to many other MPI
routines) describes the layout of memory -- Not the layout of data in
the file.
To describe the file layout you set a file view, as you have already
done a few calls earlier.
What is your memory buffer? it allocated like this:
allocate(buffer(ijsiz(ir),numrec))
which (if I am reading fortran correctly) is a contiguous chunk of memory.
If instead you had a more elaborate data structure, like a mesh of some
kind, then passing an indexed type to the read call might make more sense.
==rob
--
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA
