Hi Matthieu,
On Mar 16, 2011, at 5:09 AM, Matthieu Dorier wrote:
> Hello,
>
> I have an application that writes a big file using pHDF5, I measured the time
> spent in IO phases by each process using MPI_Wtime before the phase and right
> after closing everything (H5close). At large scale and since my filesystem
> and network are not supposed to be able to sustain such a load, I was
> expecting to see some processes getting all the available bandwidth first,
> then some slower processes, thus leading to a variance in the time for a
> process to write its piece of data. But I realized that the write times in
> all the processes were almost the same (extremely low variability, in the
> order of 0.1s). Is their a barrier within H5close when using pHDF5 (or
> H5Fclose) that forces all the participants to sync before going on? If so how
> can I retrieve the time that an individual process spends actually writing?
> Thank you
There isn't a good way to do this with the current capabilities of the
parallel I/O code in the HDF5 library. :-/ However, you could enable the MPE
reporting in your MPI implementation and use that (which will give you
information about the MPI-level I/O operations), and some/most HPC machines
give some way to track I/O operations at the next level down also (usually by
setting environment variables or MPI info objects).
That said, we are working on two projects for the HDF5 library right
now that will allow much more information to be extracted from the lower levels
of the I/O stack. We're working toward implementing a generic way to stack
virtual file drivers (VFDs) on top of each other. We're also working on
enhancements to the "logging" VFD that we currently have (which currently only
logs serial I/O operations), to extract much more useful information. Then,
once the stackable VFD interface is in place, we'll refactor the logging VFD as
a pass-through layer, allowing both serial and parallel I/O operations to be
logged. I'm not certain about the completion date for both of these, but I'll
post notices to the forum as we make progress.
Quincey
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