I have additional question about the internal progress of these non-blocking routines. I have simple test case:

err = MPI_File_iwrite_all( fh, buf, bufsize, MPI_INT, &req);

MPI_Wait(&req, &status);

Here MPI_File_iwrite_all returns immediately and profiling shows time spent in MPI_Wait.

Next, I modified example to overlap i/o with some computations:

some_compute_fun() {

.....some_flops_here......

}

err = MPI_File_iwrite_all( fh, buf, bufsize, MPI_INT, &req);

some_compute_fun();

MPI_Wait(&req, &status);

In this case I still see the similar time spent in MPI_Wait. I added MPI_Test for the non-blocking request as:

some_compute_fun() {

MPI_Test(&req, &flag, &status);

.....some_flops_here......

}

err = MPI_File_iwrite_all( fh, buf, bufsize, MPI_INT, &req);

some_compute_fun();

MPI_Wait(&req, &status);

Now I see that i/o operation progresses in background and don't see any time spent in MPI_Wait.

Few months ago I was testing non-blocking collective operations in mvapich and saw similar behaviour where I have to use few MPI_Test calls to make progress with non-blocking collectives (this will be addressed in upcoming releases).

I am testing above i/o example on my laptop and haven't tested other non-blocking collectives. Before analysing/profiling this further on production cluster / bg-q, I would like to know:

- what is the expected behaviour?

- are there any specific options that I have to use to make sure internal progress?

-Pramod

p.s. I just built mpich-3.2 with configure,make,make install on OS X, without looking into all configure options...

On Tue, Feb 9, 2016 at 3:51 AM, Rob Latham <robl@mcs.anl.gov> wrote:

On 02/08/2016 06:04 PM, pramod kumbhar wrote:

thanks! MPI_File_iwrite_all working as expected.

I'm always glad to see folks looking at the MPI-IO routines. Let us know how your research progresses.

==rob

-Pramod

On Tue, Feb 9, 2016 at 12:52 AM, Balaji, Pavan <balaji@anl.gov
<mailto:balaji@anl.gov>> wrote:

I believe it is valid to do that in split collectives. If you want
truly nonblocking nature, the standard way to do it would be to use
nonblocking collective I/O, i.e., MPI_File_iwrite_all. This is
guaranteed to not block during the MPI_File_iwrite_all call.

-- Pavan

> On Feb 8, 2016, at 5:48 PM, pramod kumbhar
<pramod.s.kumbhar@gmail.com <mailto:pramod.s.kumbhar@gmail.com>> wrote:
>
> Hello All,
>
> I am testing MPI_FIle_write_all_begin/_end and it seems like
> MPI_File_write_all_begin waits for i/o completion.
>
> Could someone confirm the implementation of these routines?
>
> Thanks,
> Pramod
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