Hi Gilles,
Le 16-03-10 23:14, Gilles Gouaillardet a écrit :
Eric,
my short answer is no.
long answer is :
- from MPI_Register_datarep()
/* The io framework is only initialized lazily. If it hasn't
already been initialized, do so now (note that MPI_FILE_OPEN
and MPI_FILE_DELETE are the only two places that it will be
initialized). */
- from mca_io_base_register_datarep()
/* Find the maximum additional number of bytes required by all io
components for requests and make that the request size */
OPAL_LIST_FOREACH(cli,
&ompi_io_base_framework.framework_components,
mca_base_component_list_item_t) {
...
}
in your case, since nor MPI_File_open nor MPI_File_delete is invoked,
the ompio component could be disabled.
but that would mean the io component selection is also based on the
fact that MPI_Register_datarep() has
been invoked or not before. i can foresee users complaining about IO
performance discrepancies just because
of one line (e.g. MPI_Register_datarep invokation) in their code.
Ok, my situation is that I want a datarep only to have a compatible
32bits code (long int) working with files written from 64bits code with
"native" datarep...
So I want to activate the datarep functionality only into 32 bits
compilation of the code...
Now, I continued my tests with "--mca io ^ompio", but I hit another
wall: when I try to use the datarep just to test it, I now have this
message:
ERROR Returned by MPI: 51
ERROR_string Returned by MPI: MPI_ERR_UNSUPPORTED_DATAREP: data
representation not supported
which is pretty similar to MPICH output...
So I am completely stuck into implementing a solution to read/write
"native" 64 bits datarep files from a 32 bits architecture...
Isn't that into the MPI-2 standard? Does it means that no MPI
implementation is standard compliant? >:)
now if MPI_File_open is invoked first, that means that
MPI_Register_datarep will fail or success based on the selected io
component (and iirc, that could be file(system) dependent within the
same application).
i am open to suggestions, but so far, i do not see a better one (other
than implementing this in OMPIO)
the patch for v1.10 can be downloaded at
https://github.com/ggouaillardet/ompi-release/commit/1589278200d9fb363d61fa20fb39a4c2fa78c942.patch
application will not crash, but fail "nicely" on MPI_Register_datarep
In reality I want a solution to read/write files with the same API (MPI
collective calls)... and produce files that are compatible between
32bits vs 64 bits architecture relative to long int issue and without
any lost of precision or performance for "native" 64bits architectures...
I saw about 4 years ago the example into the "Using MPI-2" book about
datarep, and that let me though I could easily implement a solution to
read/write files in a compatible format between architectures, even if I
choose "native" datarep under a 64 bits architecture that is the only
one really used into clusters and by our users until now... I made the
decision to code once, with all collective I/O calls, knowing I would be
able to convert int32 to int64 when needed only...
Now, I feel I made a bad choice, since no MPI implementation have this
working... or maybe there is a simple workaround? Is there an
"external64" available? Is there something written into the file about
the datarep? If not, then "native" could still be as performant as
"external64" since no conversion shall be done, but under 32bits
architectures, there shall be some io performance losts, since more
conversions will occur....
Thanks for helping me understand!
Eric
Cheers,
Gilles
On 3/11/2016 12:11 PM, Éric Chamberland wrote:
Thanks Gilles!
it works... I will continue my tests with that command line...
Until OMPIO supports this, is there a way to put a call into the code
to disable ompio the same way --mca io ^ompio does?
Thanks,
Eric
Le 16-03-10 20:13, Gilles Gouaillardet a écrit :
Eric,
I will fix the crash (fwiw, it is already fixed in v2.x and master)
note this program cannot currently run "as is".
by default, there are two frameworks for io : ROMIO and OMPIO.
MPI_Register_datarep does try to register the datarep into all
frameworks,
and successes only if datarep was successfully registered into all
frameworks.
OMPIO does not currently support this
(and the stub is missing in v1.10 so the app does not crash)
your test is successful if you blacklist ompio :
mpirun --mca io ^ompio ./int64
or
OMPI_MCA_io=^romio ./int64
and you do not even need a patch for that :-)
Cheers,
Gilles
On 3/11/2016 4:47 AM, Éric Chamberland wrote:
Hi,
I have a segfault while trying to use MPI_Register_datarep with
openmpi-1.10.2:
mpic++ -g -o int64 int64.cc
./int64
[melkor:24426] *** Process received signal ***
[melkor:24426] Signal: Segmentation fault (11)
[melkor:24426] Signal code: Address not mapped (1)
[melkor:24426] Failing at address: (nil)
[melkor:24426] [ 0] /lib64/libpthread.so.0(+0xf1f0)[0x7f66cfb731f0]
[melkor:24426] *** End of error message ***
Segmentation fault (core dumped)
I have attached the beginning of a test program that use this
function.
(and btw a totally different error occur with mpich:
http://lists.mpich.org/pipermail/discuss/2016-March/004586.html)
Can someone help me?
Thanks,
Eric
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